Mass Extinction Permian Triassic Jurassic Cretaceous Clue Search Rivers in Time For Sale

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Mass Extinction Permian Triassic Jurassic Cretaceous Clue Search Rivers in Time:
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Rivers in Time: The Search for Clues to Earth’s Mass Extinctions by Peter D. Ward.

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DESCRIPTION: Softcover: 315 pages. Publisher: Columbia University Press; (2000). Size: 8¾ x 5¾ inches, 1 pound.Size: 8¾ x 5¾ inches x ¾ inch; 1 pound. Several times in the distant past, catastrophic extinctions have swept the Earth, causing more than half of all species, from single-celled organisms to awe-inspiring behemoths, to suddenly vanish and be replaced by new life forms. Today the rich diversity of life on the Earth is again in grave danger, and the cause is not a sudden cataclysmic event but rather humankind's devastation of the environment. Is life on our planet teetering on the brink of another mass extinction? In this absorbing new book, acclaimed paleontologist Peter D. Ward answers this daunting question with a resounding yes.

Elaborating on and updating Ward's previous work, “The End of Evolution”, “Rivers in Time” delves into his newest discoveries. The book presents the gripping tale of the author's investigations into the history of life and death on Earth through a series of expeditions that have brought him ever closer to the truth about mass extinctions, past and future. First describing the three previous mass extinctions; those marking the transition from the Permian to the Triassic periods 245 million years ago; the Triassic to the Jurassic 200 million years ago; and the Cretaceous to the Tertiary 65 million years ago, Ward assesses the present devastation in which countless species are coming to the end of their evolution at the hand of that wandering, potentially destructive force called “Homo sapiens”.

The book takes readers to the Philippine Sea, now eerily empty of life, where only a few decades of catching fish by using dynamite have resulted in eviscerated coral reefs, and a dramatic reduction in the marine life the region can support. Ward travels to Canada's Queen Charlotte Islands to investigate the extinctions that mark the boundary between the Triassic and Jurassic periods. He ventures also into the Karoo desert of southern Africa, where some of Earth's earliest land life emerged from the water and stood poised to develop into mammal form, only to be obliterated during the Permian/Triassic extinction. “Rivers of Time” provides reason to marvel and mourn, to fear and hope, as it bears stark witness to the urgency of the Earth's present predicament: Ward offers powerful proof that if radical measures are not taken to protect the biodiversity of this planet, much of life as we know it may not survive.

CONDITION: NEW. New oversized softcover. Columbia University (2002) 320 pages. Unblemished except for very mild edge and corner shelf wear to the covers, principally in the form of mild rubbing to the spine head, and very faint rubbing to the spine heel, and a small crease to the bottom corner of the back cover. Though the last few pages in the book echo the small corner crease to the bottom of the back cover, except for that the pages within the book are pristine; clean, crisp, unmarked, (otherwise) unmutilated, tightly bound, unambiguously unread. Condition is entirely consistent with new stock from a bookstore environment wherein new books might show minor signs of shelfwear, consequence of simply being shelved and re-shelved. Satisfaction unconditionally guaranteed. In stock, ready to ship. No disappointments, no excuses. PROMPT SHIPPING! HEAVILY PADDED, DAMAGE-FREE PACKAGING! Meticulous and accurate descriptions! Selling rare and out-of-print ancient history books on-line since 1997. We accept returns for any reason within 30 days! #1410.1d.

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PLEASE SEE PUBLISHER, PROFESSIONAL, AND READER REVIEWS BELOW.

PUBLISHER REVIEW:

REVIEW: Is life on our planet teetering on the brink of another mass extinction? Acclaimed paleontologist Peter D. Ward answers with a resounding yes. Ward presents the gripping tale of his investigations into the history of life and death on Earth through a series of expeditions that have brought him ever closer to the truth about mass extinctions of the past Peter D. Ward is professor of geological sciences at the University of Washington, Seattle. He is the author of many books, including “Rare Earth”, “In Search of Nautilus”, “The End of Evolution”, and “On Methuselah's Trail”.

PROFESSIONAL REVIEWS:

REVIEW: Ward (Geology, University of Washington, Seattle) presents the results of his investigations into the history of life and death on earth, describing three previous mass extinctions and evaluating the present devastation in which countless species are coming to the end of their evolution due to human action. Rivers in Time is rich in information and ideas and masterfully portrays for non-paleontologists how data are collected from the fossil record and then used to test various concepts. The section on the modern mass extinction is superb, and it should concern us all. Highly recommended.

REVIEW: The pace of species extinction provoked by human rapacity may well now equal the rate of loss in the great mass extinction events that punctuate the history of life. We need a broad perspective on this most portentous of all ecological and evolutionary disasters, and who better than a paleontologist to provide it. Peter Ward ranks with the very best in this most fascinating profession, and his book should be read by all thinking and caring people.

REVIEW: The current extinction of species at the hand of Man, a crime that posterity will regard as more pernicious than the burning of the library of Alexandria, is investigated by Peter Ward with rare perception and depth of feeling. This is one of the science books every self-taught genius should have read this year.

READER REVIEWS:

REVIEW: I really like Peter Ward's books. He presently serves as my 'geological advisor', as I also am a geologist. He is not as dogmatic as some within the field of mass extinction, since he recognizes it is now becoming increasingly obvious that in most mass extinctions, these ancient 'killers' did not act alone. Early arguments in the debate of mass extinction, especially the Cretaceous-Tertiary (K/T) event, were in the form of either/or, (eg volcanism versus asteroid/comet impact), rather than one big event following and/or combining with another.

The old argument "one or the other" is now often questioned on the basis of statistics itself. You could just as well turn this logic around-if it so happened, that once in a proverbial blue moon in geological time (which is really long) TWO OR MORE events occurred at roughly the same time-wouldn't this produce a really big mass extinction??. Maybe to exterminate a large number of species against the backdrop of reasonable resistance of life to widespread extinction, more than one major event has to occur. This sort of scenario is supported, for example, by the many impact craters which have been dated and which have produce no mass extinctions. This is the general view espoused by this book. Maybe we should expect that for a 'mass extinction' event to produce a real killer blow, maybe life has to be wounded first.

Peter Ward in this book focusses on four mass extinctions- the P/T, the end Triassic, the K/T, and the present. There is good evidence for similarities -in the end Permian it is suggested to be due to life adapted to ice ages, then increased volcanism and increased CO2 with hothouse, and possible sea level changes. At the K/T it was ocean changes (?), then volcanism and increased CO2, and then impact. At the present a suprisingly similar situation appears to be occurring. Presently now it's climate change (drying of the Mediterranean, prevalence of ice ages), evolution of man (from these two possibly), and now carbon dioxide emission.

The end Triassic, along with the end Permian, are the least understood extinction events. Peter Ward takes us to the red sandstones of the Karoo (P/T), the Queen Charlotte Islands off the coast of Canada (end Triassic), and Soviet Georgia in the former USSR (K/T), to unravel some of these mysteries. The last portion of the book looks at the present extinction event-with man as the major influence. Peter Ward mentions that the start of the Triassic worldwide often contains red-beds, even near the poles-suggesting hothouse conditions. From my experience in New South Wales, Australia, this is true. The start of the Triassic in NSW is interesting in that it seems also utterly barren of coal, despite a lot of coal through the Permian. Something happened; the organisms were all dead, apparently. There are a lot of red-beds at the boundary too, hothouse conditions, even though New South Wales was near the poles at the time. It is interesting to see these sort of patterns worldwide, something strange indeed seems to have been going on at the start of the Triassic/end Permian. A good read, and a good guide to updates on extinction scenarios.

REVIEW: I've read one other book by Peter D. Ward, "The call of distant mammoths," and enjoyed it immensely, so when I saw "Rivers in Time," and recognized the author's name I snatched it up right away. The first part of this book contains condensed excerpts from earth's history, with particular emphasis on the famous and most notable extinction events found in the strata. This is preceded, and sometimes interspersed, with a brief history of geology and paleontology. Ward covers highlights relating to methods of dating sedimentary rocks using fossils, and how those techniques are anchored in radiometric dating. Ward introduces some particularly insightful information derived from some of his own field work. This adds a nice touch, and helps the reader understand a little of the flavor associated with being a field geologist. Chapter five for example, describes some work he did along the Pacific Coast of Canada, relating to the mass extinction at the end of the Triassic period, one of the five most catastrophic extinctions during the last 500 million years.

The Triassic, Permian, Cretaceous. Ward touches on them all, at least to some extent. Part III is about the Cretaceous/Tertiary event, when the dinosaurs went extinct. Here, as in other discussions, the text isn't just about the mechanics of extinction, but draws upon many ancillary issues that add depth and flavor to the discussion. Particularly interesting is his historical discussion of the scientific debate that led to the currently accepted view that a large comet or meteorite was a major (if not the major) contributor to the Cretaceous/Tertiary event. This part of the book contains interesting tidbits of information that many arm-chair scientists will, no doubt, enjoy. One passage that I underlined was the following: "... the pollen from normal plants found in that [New Mexico] region at the time suddenly disappeared, to be replaced by a pollen and spore assemblage made up almost completely of fern material. Ferns are well-known "disaster" species because they quickly move into and colonize disturbed landscapes, such as newly burned land."

Upon reading this I reflected upon the clear-cut that I had wandered across last year, with my horse, riding through the hills of the coast range in western Oregon. It was like a complete swath of destruction laid before me, with the shattered stumps of trees littering the landscape into the hazy distance, liberally punctuated with clumps of ferns. I have a hunch that the real point of Ward's book is found in section IV, "The modern mass extinction." The modern mass extinction started more than 10,000 years ago, and continues unabated today. Ward argues that we are witnessing one of the largest (if not the largest) extinction events in terms of total species lost. He lists several studies, some more alarming than others, indicating that the rate of extinction is probably in the range of thousands of species per year.

Ward never really forces the conclusion that people are the cause of these extinctions, but he does present some pretty incriminating data pointing to our species as the culprit. Mostly the evidence is circumstantial. A natural paradise exists without humans, humans arrive, mass extinction ensues. It happened in Hawaii (both with the indigenous population, and later with European invaders), the America, Australia, Madagascar, New Zeeland, and so forth. Ward also points to studies that help illustrate the complexity of extinction. Most extinctions are not caused by a single factor. And (as in the case of Madagascar) extinctions don't have to follow necessarily from hunting or otherwise deliberate killing of animals. They can (and do) happen because of habitat destruction and habitat compartmentalization and division. Something as simple as building a road through a wilderness area can be enough to tip the balance.

The cover of Ward's book shows a stark and barren landscape with dry riverbeds streaking through the sparse, brown bush. These rivers no longer run. The symbolism for extinction is deliberate. We all know that organisms and species die, but we still morn their passage. And when they die an untimely death, when their demise could have been prevented, it leaves a bitter taste of remorse and regret. As I read this book I found my self repeatedly wishing that the knowledge found between its covers could be imparted to every one of the politicians responsible for safeguarding what's left of our environment. As I tell my kids, enjoy the wilderness you see. Climb these glaciers, breath deeply the mountain air, because it is quickly disappearing. I'd call Ward's book valuable and informative, and hopefully it will spur a few to try and stop the onslaught, because extinction really is forever.

REVIEW: This book is by far one of the best books I have ever read. I now look at life in a completely different way. I was brought up in a strict Baptist home where the Bible was the only way, after reading this book I don't dismiss God but life is sure not how the Bible says it is. Peter writes this book in an informal way, which makes it very interesting; you can almost fell like you are there, taking a beginner like me into a very complicated world. I have discussed this book with others at work and found that no one that I talked to accepts evolution; they all think it's not real. I just feel so much more educated on the subject and thank Peter Ward for writing this book. It was great.

ADDITIONAL BACKGROUND:

PALEO SCIENCES:

Paleontology and Related Sub-Specialties:

Paleontology is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene Epoch. That's roughly 11,700 years before the present. The discipline includes the study of fossils so as to classify organisms, as well as the study of interactions between those organisms and their environments. The latter is a subdiscipline oftentimes referred to as observations have been documented as far back as the 5th century BC. The science became established in the 18th century as a result of Georges Cuvier's work on comparative anatomy. It then developed verely rapidly in the 19th century. The term itself originates from Greek “palaios”, meaning old or ancient, and “ontos", meaning being or creature, and “logos”, meaning speech, thought, or study".

Paleontology lies on the border between biology and geology. It differs from archaeology in that it excludes the study of anatomically modern humans. It now uses techniques drawn from a wide range of sciences, including biochemistry, mathematics, and engineering. Use of all these techniques has enabled paleontologists to discover much of the evolutionary history of life, almost all the way back to when Earth became capable of supporting life, roughly over 4 billion years ago.

The simplest definition of paleontology is "the study of ancient life". The field seeks information about several aspects of past organisms including their identity and origin, their environment and evolution, and what they can tell us about the Earth's organic and inorganic past. William Whewell (1794–1866) classified paleontology as one of the historical sciences, along with archaeology, geology, astronomy, cosmology, philology and history itself

Paleontology aims to describe phenomena of the past and to reconstruct their causes. There are three main elements to this objective. First is to describe past phenomena. Second is to develop a general theory pertaining to the causes of various types of change. Last to apply those theories to specific facts. When trying to explain the past paleontologists and other historical scientists often construct a set of one or more hypotheses about the causes. They then look for a "smoking gun".

A “smoking gun” is evidence that strongly accords with one hypothesis over any others. Sometimes researchers discover a "smoking gun" by a fortunate accident during other research. For example in 1980 researchers discovered iridium in the Cretaceous–Tertiary boundary geological layer. Iridium is principally an extraterrestrial metal. This discovery made an asteroid impact the most favored explanation for the Cretaceous–Paleogene extinction event, though there is still debate pertaining to the possible contribution of volcanism to the extinction.

As opposed to proving hypotheses about the workings and causes of natural phenomena, a complementary approach is oftentimes employed by conducting experiments to disprove hypotheses. Although this approach cannot prove a hypothesis, the accumulation of failures to disprove is often compelling evidence in favor of a hypothesis.

As knowledge has increased paleontology has developed specialized sub-divisions. Some of these sub-disciplines focus on different types of fossil organisms while others study ecology and environmental history, such as ancient climates. The latter specialty is known as “paleoclimatology”. Body fossils and trace fossils are the principal types of evidence of ancient life. Geochemical evidence has helped to decipher the evolution of life before there were organisms large enough to leave body fossils.

Estimating the age of these remains is essential but can be difficult. Sometimes adjacent rock layers allow radiometric dating, which provides absolute dates that are accurate to within 0.5%. More often however paleontologists have to rely on relative dating by solving the "jigsaw puzzles" of biostratigraphy. Biostratigraphy refers to the arrangement of rock layers from youngest to oldest.

Classifying ancient organisms is also oftentimes difficult. Many ancient organisms do not fit well into the Linnaean taxonomy system scientists use to classify living organisms. Paleontologists more often use “cladistics” to draw up evolutionary "family trees". The final quarter of the 20th century saw the development of molecular phylogenetics. This discipline investigates how closely organisms are related by measuring the similarity of the DNA in their genomes.

Molecular phylogenetics has also been used to estimate the dates when species diverged. However there occasionally exists some controversy regarding the reliability of the molecular clock on which such estimates depend. Though paleontology lies between biology and geology since it focuses on the record of past life, nonetheless its main source of evidence is fossils in rocks. For historical reasons then paleontology is part of the geology department at many universities.

In the 19th and early 20th centuries geology departments found fossil evidence important for dating rocks. Campus biology departments on the other hand showed comparsatively little evidence on fossil-bear rocks. Paleontology also has some overlap with archaeology. Archaeology primarily works with objects made by humans and with human remains. Paleontologists on the other hand are interested in the characteristics and evolution of humans as a species.

When addressing evidence about humans archaeologists and paleontologists may work together. For example paleontologists might identify animal or plant fossils around an archaeological site. This aids in the determination of what hominid populations inhabited the area and what they ate. This research might even analyze the climate at the time of habitation. In addition, paleontology often borrows techniques from other sciences, including biology, osteology, ecology, chemistry, physics and mathematics.

For example geochemical signatures from rocks may help to discover when life first arose on Earth. Analyses of carbon isotope ratios may help to identify climate changes and even to explain major transitions such as the Permian–Triassic extinction event. A relatively recent discipline, molecular phylogenetics, compares the DNA and RNA of modern organisms to re-construct the "family trees" of their evolutionary ancestors. It has also been used to estimate the dates of important evolutionary developments.

Techniques from engineering have been used to analyze how the bodies of ancient organisms might have worked. Examples would include a determination of the running speed and bite strength of Tyrannosaurus Rex. Another example would include the flight mechanics of Microraptor. Analyses using engineering techniques showed that Tyrannosaurus had a devastating bite. The same techniques raised doubts about its running ability.

It is also relatively commonplace to study the internal details of fossils using X-ray microtomography. Paleontology, biology, archaeology, and paleoneurobiology combine to study endocranial casts (endocasts) of species related to humans to clarify the evolution of the human brain. Paleontology even contributes to astrobiology. Astrobiology involves the investigation of possible life on other planets. Paleontology aids in this investigation developing models of how life may have arisen, and by providing techniques for detecting evidence of life.

Again as knowledge has increased, paleontology has developed specialized subdivisions. Elaborating on our earlier mention of this topic, vertebrate paleontology for example concentrates on fossils from the earliest fish to the immediate ancestors of modern mammals. On the other hand invertebrate paleontology deals with fossils such as molluscs, arthropods, annelid worms and echinoderms.

Further elaborative examples would include Paleobotany. Paleobotany studies fossil plants, algae, and fungi. Micropaleontology deals with microscopic fossil organisms of all kinds. Palynology is the study of pollen and spores produced by land plants and protists. This specialty straddles paleontology and botany. It deals with both living and fossil organisms.

Instead of focusing on individual organisms, paleoecology examines the interactions between different ancient organisms. This would include for example their food chains and two-way interactions with their environments. For example the development of oxygenic photosynthesis by bacteria caused the oxygenation of the atmosphere. This in turn hugely increased the productivity and diversity of ecosystems. Ultimately this led to the evolution of complex eukaryotic cells, from which all multicellular organisms are built.

Paleoclimatology although sometimes treated as part of paleoecology focuses more on the history of Earth's climate. Included in this focus are the mechanisms that have changed Earth's climate. This would include evolutionary developments. For example the rapid expansion of land plants in the Devonian period removed more carbon dioxide from the atmosphere. This had the effect of reducing the greenhouse effect. In turn this helped to cause an ice age in the Carboniferous period.

Biostratigraphy involved the use of fossils to aid in the determination of the chronological order in which rocks were formed. Biostratigraphy is useful to both paleontologists and geologists. Biogeography studies the spatial distribution of organisms. It is also linked to geology as it aids in explaining how Earth's geography has changed over time.

Fossils of organisms' bodies are usually the most informative type of evidence. The most common fossil types are wood, bones, and shells. Fossilization is a rare event to begin with. Then most fossils are destroyed by erosion or metamorphism before they can be observed. Hence the fossil record is very incomplete. This is increasingly so as science moves further and further back in time. Nonetheless the study of fossils is often adequate to illustrate the broader patterns of life's history.

There are also biases inherent in the fossil record. Different environments are more favorable to the preservation of different types of organism or parts of organisms. Furthermore only the parts of organisms that were already mineralized are usually preserved. An example would be the shells of molluscs. Since most animal species are soft-bodied they decay before they can become fossilized. As a result although there are over thirty phyla of living animals, two-thirds have never been found as fossils.

Occasionally unusual environments may preserve soft tissues. This allows paleontologists to examine the internal anatomy of animals that in other sediments which if preserved at all, are only represented by shells, spines, claws, etc. However even such fortuitous circumstances present an incomplete picture of life at the time. The majority of organisms living at the time are probably not represented. This is because the preservation of soft tissues are events restricted to a narrow range of environments.

The events would typically include situations where soft-bodied organisms were preserved very quickly by events such as mudslides. Such rare (abnormal) events which would lead to such a quick burial and preservation make it difficult to study the normal environments of the animals. The sparseness of the fossil record means that organisms are assumed to have existed long before and long after they are found in the fossil record. This is known as the “Signor–Lipps effect”.

Moving on from body fossils, trace fossils consist mainly of tracks and burrows made by extinct organisms. However trace fossils also include coprolites (fossilized feces) and marks left by feeding. Trace fossils are particularly significant because they represent a data source that is not limited to animals with easily fossilized hard parts. They are also significant in that they reflect some aspects of the organisms' behaviors.

Equally significant many trace fossils date substantially earlier than the body fossils of animals that were capable of making the trace fossils. Of course the precise assignment of trace fossils to the organisms that produced them is generally impossible. Nonetheless trace fossils may for example provide the earliest physical evidence of the appearance of moderately complex animals. These would include ancient organisms comparable in structure for example to earthworms.

Geochemical observations may help to deduce the global level of biological activity at a certain period, or the affinity of certain fossils. For example, geochemical features of rocks may reveal when life first arose on Earth. Geochemical features may also provide evidence of the presence of eukaryotic cells, the type from which all multicellular organisms are built. Analyses of carbon isotope ratios may help to explain major transitions such as the Permian–Triassic extinction event.

Naming groups of organisms in a way that is clear and widely agreed is important. Otherwise (believe it or not) some disputes in paleontology have been based merely on misunderstandings over names. Linnaean taxonomy is commonly used for classifying living organisms. However it runs into difficulties when dealing with newly discovered organisms that are significantly different from known ones. For example, it is hard to decide at what level to place a new higher-level grouping, e.g. genus or family or order. This is important since the Linnaean rules for naming groups are tied to their levels. If a group is moved to a different level then it must be renamed.

Paleontologists generally use approaches based on cladistics. Cladistics is a technique for working out the evolutionary "family tree" of a set of organisms. It works by logic. For instance if groups B and C have more similarities to each other than either has to group A, then B and C are more closely related to each other than either is to A. Characteristics that are compared may be anatomical, such as the presence of a notochord. Characteristics may also be molecular, as determined by comparing sequences of DNA or proteins.

The result of a successful analysis is a hierarchy of clades, e.g. groups that share a common ancestor. Ideally the "family tree" has only two branches leading from each node, or "junction". However sometimes there is too little information to achieve this. In those instances paleontologists have to make do with junctions that have several branches. The cladistic technique is sometimes fallible. For example some features such as wings or camera eyes evolved more than once, convergently. This must be taken into account in analyses.

Evolutionary developmental biology, commonly abbreviated to "Evo Devo", also helps paleontologists to produce "family trees" and to better understand fossils. For example the embryological development of some modern brachiopods suggests that brachiopods may be descendants of the halkieriids. Halkieriids became extinct in the Cambrian period.

Paleontology seeks to map out how living things have changed through time. A substantial hurdle to this aim is the difficulty of working out how old fossils are. Beds that preserve fossils typically lack the radioactive elements needed for radiometric dating. This technique is our only means of giving rocks greater than about 50 million years old an absolute age. The technique is particularly valuable as it can be accurate to within 0.5% or better.

Although radiometric dating requires very careful laboratory work, its basic principle is simple. The rates at which various radioactive elements decay are known. So the ratio of the radioactive element to the element into which it decays shows how long ago the radioactive element was incorporated into the rock. Radioactive elements are commonly found only in rocks with a volcanic origin. Thus the only fossil-bearing rocks that can be dated radiometrically are a few volcanic ash layers.

Consequently in the absence of such volcanic ash layers paleontologists are then left to rely on stratigraphy to date fossils. Stratigraphy is the science of deciphering the "layer-cake" that is the sedimentary record. Stratigraphy has often been compared to a jigsaw puzzle. Rocks normally form relatively horizontal layers, with each layer younger than the one underneath it. If a fossil is found between two layers whose ages are known, then obviously the fossil's age must lie between the two known ages.

However rock sequences are not continuous. They may be broken up or made discontinuous by faults or periods of erosion. Consequently it is very difficult to match up rock beds that are not directly next to one another. However fossils of species that survived for a relatively short time can be used to link up isolated rocks or rock layers. This technique is called biostratigraphy.

For instance the conodont Eoplacognathus pseudoplanus has a short range of existence in the Middle Ordovician period. If rocks of unknown age are found to have traces of E. pseudoplanus, they must have a mid-Ordovician age. Such “index fossils” must be distinctive, be globally distributed, and have a short time range to be useful. However misleading results are produced if the index fossils turn out to have longer fossil ranges than first thought.

Stratigraphy and biostratigraphy can in general provide only relative dating (A was before B), which is often sufficient for studying evolution. However this is difficult for some time periods, because of the problems involved in matching up rocks of the same age across different continents. Family-tree relationships may also help to narrow down the date when lineages first appeared.

For instance if fossils of B or C date to X million years ago and the calculated "family tree" says A was an ancestor of B and C, then A must have evolved more than X million years ago. It is also possible to estimate how long ago two living clades diverged – i.e. approximately how long ago their last common ancestor must have lived – by assuming that DNA mutations accumulate at a constant rate.

These "molecular clocks" however are fallible. At best they provide only a very approximate timing. For example they are not sufficiently precise and reliable for estimating when the groups that feature in the Cambrian explosion first evolved. The estimates derived from applying the different techniques may vary by a factor of two.

Earth formed about 4,570 million (4.57 billion) years ago. A collision that formed the Moon occurred about 40 million years later, about 4.53 billion years ago. Earth may thereafter have cooled quickly enough to have oceans and an atmosphere by about 4.44 billion years ago. There is evidence on the Moon of a Late Heavy Bombardment by asteroids from about/between 4 and 3.8 billion years ago. It's likely that this bombardment struck the earth at the same time. If so, the bombardment may have stripped away those first atmosphere and oceans.

Paleontology traces the evolutionary history of life back to over 3 billion years ago, possibly as far as 3.8 billion years ago. The oldest clear evidence of life on Earth dates to 3 billion years ago. However there have been reports (often disputed) of fossil bacteria from 3.4 billion years ago. There is also believed by many to be geochemical evidence for the presence of life 3.8 billion years ago, shortly after the cessation of the asteroid bombardment.

Some scientists have proposed that life on Earth was "seeded" from elsewhere. However but most research concentrates on various explanations of how life could have arisen independently on Earth. For about 2 billion years microbial mats were the dominant life on Earth. There microbial mats were multi-layered colonies of different bacteria. The evolution of oxygenic photosynthesis enabled them to play the major role in the oxygenation of the atmosphere starting about 2.4 billion years ago.

This change in the atmosphere increased their effectiveness as nurseries of evolution. Eukaryotes were cells with complex internal structures. While they may have been present earlier, their evolution speeded up when they acquired the ability to transform oxygen from a poison to a powerful source of metabolic energy. This innovation may have come from primitive eukaryotes capturing oxygen-powered bacteria as endosymbionts and transforming them into organelles called mitochondria.

The earliest evidence of complex eukaryotes with organelles (such as mitochondria) dates from 1.85 billion years ago. Multicellular life is composed only of eukaryotic cells. The earliest evidence for multicellular life is found in the Francevillian Group Fossils from 2.1 billion years ago. However specialization of cells for different functions only first appears between 1.43 million years ago (a possible fungus) and 1.2 billion years ago (a probable red alga).

Sexual reproduction is likely a prerequisite for specialization of cells. Otherwise asexual multicellular organism might be at risk of being taken over by rogue cells that retain the ability to reproduce. The earliest known animals are cnidarians from about 580 million years ago. However these are so modern-looking that they must be descendants of earlier animals yet unknown to science.

Early fossils of animals are rare. This is because they had not developed mineralized, easily fossilized hard parts until about 548 million years ago. The earliest modern-looking bilaterian animals appear in the Early Cambrian. These appeared alongside several "weird wonders" that bear little obvious resemblance to any modern animals.

There is a long-running debate about whether this Cambrian explosion was truly a very rapid period of evolutionary experimentation. Alternative views are that modern-looking animals began evolving earlier, but fossils of their precursors have not yet been found. Another alternate view postulated is that the "weird wonders" are evolutionary "aunts" and "cousins" of modern groups.

Vertebrates remained a minor group until the first jawed fish appeared in the Late Ordovician. Haikouichthys, from about 518 million years ago in China, may be the earliest known fish. The lineage that produced land vertebrates evolved over 100 million years later. The spread of animals and plants from water to land required organisms to solve several problems. These challenges including protection against drying out and supporting themselves against gravity.

The earliest evidence of land plants and land invertebrates date back to about 476 million years ago and 490 million years ago respectively. As indicated by their trace and body fossils those early invertebrates were arthropods known as euthycarcinoids. However they evolved very rapidly between 370 million years ago and 360 million years ago.

Recent discoveries have overturned earlier ideas about the history and driving forces behind their evolution. Land plants were so successful that their detritus caused an ecological crisis in the Late Devonian. This crisis was only resolved by the evolution of fungi that could digest dead wood.

During the Permian period synapsids, including the ancestors of mammals, may have dominated land environments. However this domination ended with the Permian–Triassic extinction event 251 million years ago. The Permian-Triassic extinction event came very close to wiping out all complex life. The extinctions were apparently fairly sudden, at least among vertebrates.

During the slow recovery from this catastrophe a previously obscure group, archosaurs, became the most abundant and diverse terrestrial vertebrates. One archosaur group were the dinosaurs. They became the dominant land vertebrates for the rest of the Mesozoic. Birds evolved from one group of dinosaurs. During this time mammals' ancestors survived only as small, mainly nocturnal insectivores. This niche may have accelerated the development of mammalian traits such as endothermy and hair.

The Cretaceous–Paleogene extinction event 66 million years ago killed off all the dinosaurs except the birds. Birds are the only surviving dinosaurs. After the Cretaceous-Paleogene extinction mammals increased rapidly in size and diversity. Aside from their land-based populations, some took to the air and the sea.

Fossil evidence indicates that in the meanwhile flowering plants had appeared and rapidly diversified in the Early Cretaceous. This occurred during between 130 million years ago and 90 million years ago. The rapid rise of flowering plants to dominance of terrestrial ecosystems is thought to have been propelled by co-evolution with pollinating insects. Social insects had appeared around the same time. Although they account for only small parts of the insect "family tree", social insects now form over 50% of the total mass of all insects.

Humans evolved from a lineage of upright-walking apes. The earliest fossils date from over 6 million years ago. Early members of this lineage had chimp-sized brains, about 25% as big as modern humans'. However there are signs of a steady increase in brain size after about 3 million years ago. There is a long-running debate about whether modern humans are descendants of a single small population in Africa. It is proposed by many researchers that this single population then migrated all over the world less than 200,000 years ago and replaced previous hominine species. The alternate theory is that modern humans arose worldwide roughly at the same time as a result of interbreeding, and originated from a number of populations.

Life on earth has suffered occasional mass extinctions at least since 542 million years ago. Despite their disastrous effects, mass extinctions have sometimes accelerated the evolution of life on earth. When dominance of an ecological niche passes from one group of organisms to another, this is rarely because the new dominant group out-competes the old. Rather it is usually because an extinction event allows a new group to outlive the old and move into its niche.

The fossil record appears to show that the rate of extinction is slowing down. Both the gaps between mass extinctions are becoming longer, and the average and background rates of extinction decreasing. However it is not absolutely certain whether the actual rate of extinction has altered. Both of these observations pertaining to a slowing extinction rate could be explained in several ways.

For instances the oceans may have become more hospitable to life over the last 500 million years. Thus they would be less vulnerable to mass extinctions. Dissolved oxygen has become more widespread and penetrated to greater depths. The development of life on land reduced the run-off of nutrients. This would reduce the risk of eutrophication and anoxic events. Marine ecosystems have also become more diversified so that food chains are less likely to be disrupted.

Reasonably complete fossils are very rare. Most extinct organisms are represented only by partial fossils. Complete fossils are of course rarest in the oldest rocks. So paleontologists have mistakenly assigned parts of the same organism to different genera. This after the genera were created and defined solely to accommodate these finds. The risk of this mistake is higher for older fossils because these are often unlike parts of any living organism. Many "superfluous" genera are represented by fragments that are not found again. These "superfluous" genera are interpreted as having become extinct very quickly.

Biodiversity in the fossil record is "the number of distinct genera alive at any given time; that is, those whose first occurrence predates and whose last occurrence postdates that time". Biodiversity shows shows a different trend than a slowing extinction rate. Biodiversity exhibited a fairly swift rise from 542 to 400 million years ago. Then a slight decline from 400 to 200 million years ago. The devastating Permian–Triassic extinction event was an important factor in that decline. Then after the Permian-Triassic extinction event a swift rise in biodiversity from 200 million years ago to the present.

Although paleontology became established around 1800, earlier thinkers had noticed aspects of the fossil record. The ancient Greek philosopher Xenophanes (570–480 BC) concluded from fossil sea shells that some areas of land were once under water. During the Middle Ages the Persian naturalist Ibn Sina, known as Avicenna in Europe, discussed fossils. Ibn Sina proposed a theory of petrifying fluids on which Albert of Saxony elaborated in the 14th century.

The Chinese naturalist Shen Kuo (1031–1095 AD) proposed a theory of climate change based on the presence of petrified bamboo. The petrified bamboo was found in regions that in his time were too dry for bamboo. In early modern Europe the systematic study of fossils emerged as an integral part of the changes in natural philosophy that occurred during the Age of Reason. In the Italian Renaissance Leonardo da Vinci made various significant contributions to the field as well depicted numerous fossils.

Leonardo's contributions are central to the history of paleontology. Leonardo established a line of continuity between the two main branches of paleontology – ichnology and body fossil paleontology. Ichnofossils were structures left by living organisms. Ichnofossils are significant paleoenvironmental tools as certain ichnofossils show the marine origin of rock strata. Ichnofossils are distinct from body fossils, but can be integrated with body fossils to provide paleontological information. This demonstrates the independence and complementary evidence of ichnofossils and body fossils.

At the end of the 18th century Georges Cuvier's work established comparative anatomy as a scientific discipline. By proving that some fossil animals resembled no living ones he demonstrated that animals could become extinct. This revelation led to the emergence of paleontology. The expanding knowledge of the fossil record also played an increasing role in the development of geology, particularly stratigraphy.

First mention of the word paleontology (“palæontologie”) was in January 1822 by Henri Marie Ducrotay de Blainville in his Journal de physique. He coined the word "palaeontology" to refer to the study of ancient living organisms through fossils. The first half of the 19th century saw geological and paleontological activity become increasingly well organized. This period witnessed the growth of geologic societies and museums. As well there was an increasing number of professional geologists and fossil specialists.

Interest increased for reasons that were not purely scientific. For instance geology and paleontology helped industrialists to find and exploit natural resources such as coal. This contributed to a rapid increase in knowledge about the history of life on Earth. This also led to progress in defining the geologic time scale, which was largely based on fossil evidence. As knowledge of life's history continued to improve, it became increasingly obvious that there had been some kind of successive order to the development of life. This encouraged early evolutionary theories on the transmutation of species.

After Charles Darwin published Origin of Species in 1859 much of the focus of paleontology shifted to understanding evolutionary paths. These pathways included human evolution and evolutionary theory. The last half of the 19th century saw a tremendous expansion in paleontological activity. This was especially evident in North America. The trend continued in the 20th century with additional regions of the Earth being opened to systematic fossil collection.

Fossils found in China near the end of the 20th century have been particularly important. They have provided new information about the earliest evolution of animals, early fish, dinosaurs and the evolution of birds. The last few decades of the 20th century has also witnessed a strongly renewed interest in mass extinctions and their role in the evolution of life on Earth. There has also been a renewed interest in the Cambrian Explosion that apparently saw the development of the body plans of most animal phyla. The discovery of fossils of the Ediacaran biota and developments in paleobiology extended knowledge about the history of life back far before the Cambrian.

Increasing awareness of Gregor Mendel's pioneering work in genetics led first to the development of population genetics and then in the mid-20th century to the modern evolutionary synthesis. This explains evolution as the outcome of events such as mutations and horizontal gene transfer. These events provide genetic variation, with genetic drift and natural selection driving changes in this variation over time. Within the next few years the role and operation of DNA in genetic inheritance were discovered. This led to what is now known as the "Central Dogma" of molecular biology.

In the 1960's molecular phylogenetics began to make an impact. Molecular phylogenetics involves the investigation of evolutionary "family trees" by techniques derived from biochemistry. The impact of molecular phylogenetics has been particularly significant in suggesting that the human lineage had diverged from apes much more recently than was generally assumed. Although this early study compared proteins from apes and humans, most molecular phylogenetics research is now based on comparisons of RNA and DNA.

Paleobiology:Paleobiology is a growing and comparatively new discipline which combines the methods and findings of the life science biology with the methods and findings of earth science paleontology. It is occasionally referred to as geobiology. Paleobiological research uses biological field research of current biota and of fossils millions of years old to answer questions about the molecular evolution and the evolutionary history of life. In this scientific quest, macrofossils, microfossils and trace fossils are typically analyzed. In addition however 21st century biochemical analysis of DNA and RNA samples offers much promise, as does the biometric construction of phylogenetic trees.

Related sub-specialties include:

Paleobotany, which applies the principles and methods of paleobiology to flora, especially green land plants. However paleobotany also includes the fungi and seaweeds (algae). Paleobotany also involves mycology, phycology and dendrochronology.

Paleozoology uses the methods and principles of paleobiology to understand fauna, both vertebrates and invertebrates. Paleozoology also involves vertebrate and invertebrate paleontology, as well as paleoanthropology.

Micropaleontology applies paleobiologic principles and methods to archaea, bacteria, protists and microscopic pollen/spores. It also involves the study of microfossils and palynology.

Paleovirology examines the evolutionary history of viruses on paleobiological timescales.

Paleobiochemistry uses the methods and principles of organic chemistry to detect and analyze molecular-level evidence of ancient life, both microscopic and macroscopic.

Paleoecology examines past ecosystems, climates, and geographies so as to better comprehend prehistoric life.

Taphonomy analyzes the post-mortem history of individual organisms. This history would, for example, include decay and decomposition. Researchers thus gain insights into the behavior, death and environment of the fossilized organisms.

Paleoichnology analyzes the tracks, borings, trails, burrows, impressions, and other trace fossils left by ancient organisms. This allows researchers to gain insights into the behavior and ecology of the ancient organisms.

Stratigraphic paleobiology studies long-term secular changes as well as the (short-term) bed-by-bed sequence of changes in the characteristics and behaviors or ancient organisms. This sub-discipline is closed related to studies of stratification, sedimentary rocks, and the geologic time scale.

Evolutionary developmental paleobiology examines the evolutionary aspects of the modes and trajectories of growth and development in the evolution of life. This includes organisms both extinct and extant. The sub-discipline is closed related to studies of adaptive radiation, cladistics, evolutionary biology, developmental biology and phylogenetic trees.

The founder or "father" of modern paleobiology was Baron Franz Nopcsa who lived from 1877 to 1933). Nopcsa was a Hungarian scientist trained at the University of Vienna. He initially termed the discipline "paleophysiology." Credit for coining the word paleobiology itself goes to Professor Charles Schuchert. He proposed the term in 1904. His stated intent was to initiate "a broad new science" joining "traditional paleontology with the evidence and insights of geology and isotopic chemistry."

Charles Doolittle Walcott has been cited as the "founder of Precambrian paleobiology." Walcott was a Smithsonian adventurer. Walcott is best known to history as the discoverer of the mid-Cambrian Burgess shale animal fossils. In 1883 this American curator found the "first Precambrian fossil cells known to science". This was in the form of a stromatolite reef then known as Cryptozoon algae. In 1899 Walcott discovered the first acritarch fossil cells. These were a Precambrian algal phytoplankton he named “Chuaria”. And finally in 1914 Walcott reported "minute cells and chains of cell-like bodies" belonging to Precambrian purple bacteria.

Later 20th century paleobiologists have also figured prominently in finding Archaean and Proterozoic eon microfossils. In 1954 Stanley A. Tyler and Elso S. Barghoorn described 2.1 billion-year-old cyanobacteria and fungi-like microflora at their Gunflint Chert fossil site. Eleven years later in 1965 Barghoorn and J. William Schopf reported finely-preserved Precambrian microflora at their Bitter Springs site of the Amadeus Basin, Central Australia. Then in 1993 Schopf discovered O2-producing blue-green bacteria at his 3.5 billion-year-old Apex Chert site in Pilbara Craton, Marble Bar, in the northwestern part of Western Australia. So paleobiologists were at last homing in on the origins of the Precambrian "Oxygen catastrophe."

Paleoclimatology: Paleoclimatology is the study of climates for which direct measurements were not taken. As instrumental records only span a tiny part of Earth's history, the reconstruction of ancient climate is important. This enables researchers to better understand natural variation and the evolution of the current climate. Paleoclimatology uses a variety of proxy methods from Earth and life sciences to obtain data previously preserved within rocks, sediments, boreholes, ice sheets, tree rings, corals, shells, and microfossils. Combined with techniques to date the proxies, these paleoclimatological records are used to determine the past states of Earth's atmosphere.

The scientific field of paleoclimatology came to maturity in the 20th century. Notable periods studied by paleoclimatologists are many. These include the frequent glaciations Earth has undergone. Also the rapid cooling events such as the Younger Dryas. And as well the fast rate of warming during the Paleocene–Eocene Thermal Maximum. Studies of past changes in the environment and biodiversity often reflect on the current situation. This to specifically include the impact of climate on mass extinctions and biotic recovery, as well as how this might affect the current period of global warming.

Notions of a changing climate probably evolved in ancient Egypt, Mesopotamia, the Indus Valley and China. There prolonged periods of droughts and floods were experienced. In the 17th century Robert Hooke postulated that fossils of giant turtles found in Dorset could only be explained by a once warmer climate. He attributed the warmer climate as the result of a shift in Earth's axis. Keep in mind that at that point in tome fossils were often explained as a consequence of a Biblical flood. It was not until the 19th century that systematic observations of sunspots started by amateur astronomer initiated a discussion pertaining to the Sun's influence on Earth's climate.

Still early in the 19th century the scientific study of paleoclimatology began to further take shape. This occurred when discoveries about glaciations and natural changes in Earth's past climate helped explain and understand the greenhouse effect. But it was only in the 20th century that paleoclimatology became a unified scientific field. Before then different aspects of Earth's climate history were studied by a variety of disciplines.

By the end of the 20th century the empirical research into Earth's ancient climates started to be combined with computer models of increasing complexity. A new objective also developed in this period. That was finding ancient analog climates that could provide information about current climate change. Today paleoclimatologists employ a wide variety of techniques to deduce ancient climates.

The techniques employed are dependent on what variables have to be reconstructed. These might include for instance temperature, precipitation, or some other aspect of past climates. These techniques are also variable based on how long ago the climate of interest occurred. For instance the deep marine record is the source of most isotopic data. However this record exists only on oceanic plates. These records disappear when the oceanic plates are eventually subducted. The oldest remaining material is 200 million years old. Additionally older sediments are also more prone to corruption by diagenesis. Resolution and confidence in the data decrease over time. Mountain glaciers and the polar ice caps/ice sheets provide much data in paleoclimatology. Ice-coring projects in the ice caps of Greenland and Antarctica have yielded data going back several hundred thousand years. In the case of the EPICA project the sample cores actually dated over 800,000 years ago.

Air trapped within fallen snow becomes encased in tiny bubbles. Then the snow is compressed into ice in the glacier under the weight of later years' snow. The trapped air has proven a tremendously valuable source for direct measurement of the composition of air from the time the ice was formed. Layering can be observed because of seasonal pauses in ice accumulation. The naturally occurring layering can be used to establish chronology, associating specific depths of the core with ranges of time. Changes in the layering thickness can also be used to determine changes in precipitation or temperature.

The varying amount of oxygen-18 isotope found in ice layers represent changes in average ocean surface temperature. Water molecules containing the heavier O-18 evaporate at a higher temperature than water molecules containing the normal Oxygen-16 isotope. The ratio of O-18 to O-16 will be higher as temperature increases. The ratio of O-18 to O-16 is also influenced by other factors such as the water's salinity and the volume of water locked up in ice sheets. Various historical cycles in those isotope ratios have been recorded.

Pollen has been observed in ice cores and has been used to understand which plants were present as the layer formed. Pollen is produced in abundance and its distribution is typically well understood. A pollen count for a specific layer can be determined by observing the total amount of pollen categorized by type in a controlled sample of that layer. Changes in plant frequency over time can be plotted through statistical analysis of pollen counts in the core.

Knowing which plants were present leads to an understanding of precipitation and temperature, and types of fauna present. Palynology includes the study of pollen for these purposes. In addition volcanic ash is contained in some layers. The ash can be used to establish the time of the formation of the layer of ice. Each volcanic event distributes ash with a unique set of properties. These properties include the shape and color of particles, as well as the chemical signature of the ice. Establishing the ash's source will establish a range of time to associate with layer of ice.

A multinational consortium drilled an ice core in Dome C on the East Antarctic ice sheet. The consortium is known as the European Project for Ice Coring in Antarctica (EPICA). EPICA was able to retrieve ice core samples from layers created roughly 800,000 years ago. The international ice core community has defined a priority project to obtain the oldest possible ice core record from Antarctica. Under the auspices of International Partnerships in Ice Core Sciences (IPICS) an effort will be made to retrieve an ice core record reaching back to 1.5 million years ago.

Climatic information can be obtained through an understanding of changes in tree growth. Generally trees respond to changes in climatic variables by speeding up or slowing down growth. This growth pattern is in turn generally reflected by a greater or lesser thickness in growth rings. A tree-ring record is established by compiling information from many living trees in a specific area. It is important to note however that different species respond to changes in climatic variables in different ways.

Some older intact wood samples fortuitously escape decay can. These intact samples can extend the time covered by the dendrotic record. This is achieved by matching the ring depth changes to contemporary specimens. By using that method some areas have tree-ring records dating back a few thousand years. Older wood not connected to a contemporary record can be dated generally with radiocarbon techniques. A tree-ring record can be used to produce information regarding precipitation, temperature, hydrology, and fire corresponding to a particular area.

In working with longer time scales geologists must refer to the sedimentary record for data. Sediments are sometimes lithified to form rock. These sedimentary rocks may contain remnants of preserved vegetation, animals, plankton, or pollen. These preserved organic remains may help establish the characteristics of certain climatic zones. Biomarker molecules such as the alkenones may yield information about their temperature of formation. Chemical signatures as well can be used to reconstruct past temperature. This is particularly so of the Mg/Ca ratio of calcite in Foraminifera tests.

Isotopic ratios can provide further information. Specifically the O-18 isotope record responds to changes in temperature and ice volume. The O-13 isotope record reflects a wide range of factors which are often more difficult to disentangle, identify, and quantify. Sedimentary sea floor core sample are labeled to identify the exact spot on the sea floor where the sample was taken. Sediments from nearby locations can show significant differences in chemical and biological composition.

On a longer time scale, the rock record may show signs of sea level rise and fall. Oftentimes features such as "fossilized" sand dunes can be identified. Scientists can get a grasp of long term climate by studying sedimentary rock going back billions of years. The division of earth history into separate periods is largely based on visible changes in sedimentary rock layers that demarcate major changes in conditions. Often they include major shifts in climate.

The study of fossilized coral is known as “sclerochronology”. Coral "rings" are similar to tree rings except that they respond to a wider variety of ecological stimuli. These influences include water temperature, freshwater influx, pH changes, and wave action. From those “records” specialized equipment can be used to deduce the sea surface temperature and water salinity from the past few centuries. The O-18 isotope range of coralline red algae provides a useful proxy of the combined sea surface temperature and sea surface salinity at high latitudes and the tropics, where many traditional techniques are limited.

Within climatic geomorphology one approach often utilized by the discipline's researchers is to study relict landforms and thereby infer ancient climates. The study of past climates climatic geomorphology is considered by some researchers to be a theme of historical geology. However climatic geomorphology is of limited use to study recent (Quaternary, Holocene) large climate changes. This is due to the fact that these are seldom discernible in the geomorphological record.

The field of geochronology has scientists working on determining how old certain proxies are. For recent proxy archives of tree rings and corals the individual year rings can be counted and an exact year can be determined. Radiometric dating uses the properties of radioactive elements in proxies. In older material more of the radioactive material will have decayed. Thus the proportion of different elements will be different when contrasted with newer proxies.

One example of radiometric dating is radiocarbon dating. In the air cosmic rays constantly convert nitrogen into a specific radioactive carbon isotope known as “14C”. Plants then use this carbon to grow. However this isotope is not replenished anymore when the plant ties, and the 14C starts decaying. The proportion of 'normal' carbon and Carbon-14 gives information of how long the plant material has not been in contact with the atmosphere.

Knowledge of precise climatic events decreases as the record goes back in time, but some notable climate events are known. The first notable climactic event of course is at earth's beginning, and is known as the “Faint Young Sun Paradox”. Following is the “Huronian Glaciation” of about 2.4 billion years ago. At the point in time Earth was completely covered in ice, probably due to the “Great Oxygenation Event”. The “Later Neoproterozoic Snowball Earth” of about 600 million years ago was the precursor to the “Cambrian Explosion”.

Following was the “Andean-Saharan Glaciation” of about 450 million years ago. Following that was the “Carboniferous Rainforest Collapse” of about 300 million years ago. The the Earth's climate was rocked by the “Permian–Triassic Extinction Event of 251.4 million years ago. Thereafter followed a number of “Oceanic Anoxic Events”, notably those of about 120 and 93 million years ago, and later followed by other such events.

This was followed by yet another trauma to Earth known as the “Cretaceous–Paleogene Extinction Event of about 66 million years ago. This was followed by what is known as the “Paleocene–Eocene Thermal Maximum” of 55 million years ago. Then by the most recent “ice age” known as the “Younger Dryas” or “The Big Freeze” or about 11,000 BC. As the ice age receded Earth basked in the “Holocene climatic optimum” of about 7,000 through 3,000 BC. There were extreme weather events of 535-536 AD. This was followed by the “Medieval Warm Period” between about 900 and 1300 AD. This was followed by the “Little Ice Age” of 1300 to 1800 AD. And finally the most notable climatic event of the recent past, the “Year Without a Summer” of 1816.

Moving on the the study of Earth's past atmospheres, the first atmosphere would have consisted of gases in the solar nebula, primarily hydrogen. In addition, there would probably have been simple hydrides such as those now found in gas giants like Jupiter and Saturn. These would have principally consisted of water vapor, methane, and ammonia. As the solar nebula dissipated these gases would have escaped the atmosphere, in part driven off by the solar wind.

Earth's next atmosphere would have consisted largely of nitrogen, carbon dioxide, and inert gases. The atmosphere was produced by outgassing from volcanism. The gasses produced by volcanism would have been supplemented supplemented the by gases produced during the late heavy bombardment of Earth by huge asteroids. A major part of carbon dioxide emissions produced to have been rapidly dissolved in water and built up as carbonate sediments.

Such water-related sediments have been found dating from as early as 3.8 billion years ago. About 3.4 billion years ago nitrogen was the major part of the then stable "second atmosphere". An influence of life has to be taken into account rather soon in the history of the atmosphere because hints of early life forms have been dated to as early as 3.5 billion years ago. The fact that it is not perfectly in line with the early sun's 30% lower solar radiance (compared to today) of the has been described as the "Faint Young Sun Paradox".

The geological record shows a continually and relatively warm surface during the complete early temperature record of Earth. The only significant exception was a cold glacial phase about 2.4 billion years ago. In the late Archaean eon an oxygen-containing atmosphere began to develop. The apparent cause was photosynthesizing cyanobacteria which have been found as stromatolite fossils from 2.7 billion years ago. Scientists refer to this as “the Great Oxygenation Event'.

The early basic carbon isotopy (isotope ratio proportions) was very much in line with what is found today. This fact suggests that the fundamental features of the carbon cycle were established as early as 4 billion years ago. The constant rearrangement of continents by plate tectonics influences the long-term evolution of the atmosphere. This process transfers carbon dioxide to and from large continental carbonate stores.

Free oxygen did not exist in the atmosphere until about 2.4 billion years ago, this during the Great Oxygenation Event. The appearance of free atmospheric oxygen is indicated by the end of the banded iron formations. Until then any oxygen produced by photosynthesis was consumed by oxidation of reduced materials, notably iron. Molecules of free oxygen did not start to accumulate in the atmosphere until the rate of production of oxygen began to exceed the availability of reducing materials.

At that point there was a shift from a reducing atmosphere to an oxidizing atmosphere. Atmospheric oxygen levels showed major variations until reaching a steady state of more than 15% by the end of the Precambrian. The succeeding time span was the Phanerozoic eon. It was at this point in the history of life that oxygen-breathing metazoan life forms began to appear. The amount of oxygen in the atmosphere has fluctuated over the last 600 million years. It reached a peak of 35% during the Carboniferous period. That was significantly higher than today's 21%.

Two main processes govern changes in the atmosphere. The first is the fact that plants use carbon dioxide from the atmosphere and in turn release oxygen back into the atmosphere. The second process involves the breakdown of pyrite and volcanic eruptions which release sulfur into the atmosphere. This oxidizes and that reduces the amount of oxygen in the atmosphere. However volcanic eruptions also release carbon dioxide, which plants can convert to oxygen.

The precise causes of the historical variations of the amount of oxygen in the atmosphere is not known. Periods with much oxygen in the atmosphere are associated with rapid development of animals. Today's atmosphere contains 21% oxygen. This is high enough for rapid development of animals.

Amongst the most profound influences in the history of earth have been the various glacial events. The Huronian glaciation is the first known glaciation in Earth's history. It lasted from about 2.4 to 2.1 billion years ago, The Cryogenian glaciation lasted from 720 to 635 million years ago. The Andean-Saharan glaciation lasted from 450 to 420 million years ago. The Karoo glaciation lasted from 360 to 260 million years ago.

We're presently in the Quaternary glaciation. It is the current glaciation period and began 2.58 million years ago. In 2020 scientists published a continuous, high-fidelity record of variations in Earth's climate during the past 66 million years. The study identified four climate states, separated by transitions that include changing greenhouse gas levels and polar ice sheets volumes. They integrated the data of various sources. The warmest climate state since the time of the dinosaur extinction is known as the "Hothouse". It lasted from about 56 to 47 million years ago. The mean average temperature on the plant was 25 degrees warmer than today (14C).

The climate of the late Precambrian showed some major glaciation events spreading over much of the earth. At this time the continents were bunched up in the Rodinia supercontinent. Massive deposits of tillites and anomalous isotopic signatures are found. The presence of these deposits gave rise to the Snowball Earth hypothesis. As the Proterozoic Eon drew to a close the Earth started to warm up.

By the dawn of the Cambrian and the Phanerozoic life forms were abundant and gave rise to what is known as “the Cambrian explosion”. At that point in time the average global temperatures were around 72 (22C). The Phanerozoic climate refers to the most recent 500 million years which has witnessed variances in the oxygen (18) isotope ratios, indicating climate change events.

Major drivers for the preindustrial ages have been variations of the sun, volcanic ashes and exhalations, relative movements of the earth towards the sun, and tectonically induced effects as for major sea currents, watersheds, and ocean oscillations. In the early Phanerozoic increased atmospheric carbon dioxide concentrations have been linked to driving or amplifying increased global temperatures. Research has determined a climate sensitivity for the latter Phanerozoic which was calculated to be similar to today's modern range of values.

The difference in global mean temperatures between a fully glacial Earth and an ice free Earth is estimated at approximately 18 degrees farenheit (10 degrees centigrade). Of course far larger changes would have been observed at higher latitudes, and smaller ones at low latitudes. One requirement for the development of large scale ice sheets seems to be the arrangement of continental land masses at or near the poles. The constant rearrangement of continents by plate tectonics can also shape long-term climate evolution.

However the presence or absence of land masses at the poles is not sufficient to guarantee glaciations or exclude polar ice caps. Evidence exists of past warm periods in Earth's climate when polar land masses similar to Antarctica were home to deciduous forests rather than ice sheets. The relatively warm local minimum between the Jurassic and Cretaceous goes along with an increase of subduction and mid-ocean ridge volcanism. These were due to the breakup of the Pangea supercontinent.

Superimposed on the long-term evolution between hot and cold climates have been many short-term fluctuations in climate. These have been both similar to and sometimes more severe than the varying glacial and interglacial states of the present ice age. Some of the most severe fluctuations may be related to rapid climate changes due to sudden collapses of natural methane clathrate reservoirs in the oceans.

One such example was the “Paleocene-Eocene Thermal Maximum”. A similar, single event of induced severe climate change after a meteorite impact has been proposed as reason for the Cretaceous–Paleogene extinction event. Other major thresholds are the Permian-Triassic and Ordovician-Silurian extinction events with various reasons suggested.

Ice core data for the past 800,000 years has enabled great insights into the Quaternary climate. The Quaternary geological period includes the current climate. There has been a cycle of ice ages for the past 2.2–2.1 million years. These actually started before the Quaternary, in the late Neogene Period. The data reveal cycles of about 120,000 years. It has been observed that ice ages deepen by progressive steps, but the recovery to interglacial conditions occurs in one big step.

Climate forcing is the difference between radiant energy (sunlight) received by the Earth and the outgoing longwave radiation back to space. Radiative forcing is quantified based on the CO2 amount in the tropopause. Dependent on the radiative balance of incoming and outgoing energy, the Earth either warms up or cools down. Earth radiative balance originates from changes in solar insolation and the concentrations of greenhouse gases and aerosols. Climate change may be due to internal processes in Earth sphere's and/or following external forcings.

The Earth's climate system involves the atmosphere, biosphere, cryosphere, hydrosphere, and lithosphere. The sum of these processes from Earth's spheres is what affects the climate. Greenhouse gasses act as the internal forcing of the climate system. Particular interests in climate science and paleoclimatology focus on the study of earth climate sensitivity in response to the sum of forcings.

External forcings include the Milankovitch cycles which determine both the distance between earth and the sun as well as the orientation of earth to the sun. Forcings also include solar insolation, which is the total amount of solar radiation received by Earth. Volcanic eruptions are also considered an external forcing. They also include human changes influencing the composition of the atmosphere as well as influences pertaining to land use.

On timescales of millions of years the uplift of mountain ranges and subsequent weathering processes of rocks and soils are an important part of the carbon cycle. This includes as well the subduction of tectonic plates. The weathering sequesters CO2 include the reaction of minerals with chemicals, especially silicate weathering with CO2. This removes CO2 from the atmosphere and reduces the radiative forcing. The opposite effect is volcanism. Volcanism is be responsible for a natural greenhouse effect by emitting CO2 into the atmosphere. This affects glaciation (Ice Age) cycles.

Scientists suggest that humans emit CO2 10,000 times faster than natural processes have done in the past. Other players include ice sheet dynamics and continental positions, as well as consequential vegetation changes. All of these have been and continue to be important factors in the long term evolution of the earth's climate. There is also a close correlation between CO2 and temperature, where CO2 levels have a strong control over global temperatures in Earth history. Paleoclimatology: Historical geology or paleogeology is a discipline that uses the principles and techniques of geology to reconstruct and understand the geological history of Earth. It focuses on geologic processes that change the Earth's surface and subsurface. It employs stratigraphy, structural geology and paleontology to determine the sequence of these events. Paleogeology also focuses on the evolution of plants and animals during different time periods in the geological timescale.

The discovery of radioactivity and the development of several radiometric dating techniques in the first half of the 20th century provided a means of deriving absolute versus relative ages of geologic history. A sub-specialty known as “economic geology” is involves the search for and extraction of fuel and raw materials. Economic geology is heavily dependent on an understanding of the geological history of an area. Another sub-specialty is environmental geology. Its focus includes most significantly the study of the geologic hazards of earthquakes and volcanism. This sub-specialty as well is heavily dependent on detailed knowledge of geologic history.

Nicolaus Steno was the first to observe and propose some of the basic concepts of historical geology. Also known as as Niels Stensen he is considered to be the "father of geology". One of his (then) controversial and revolutionary concepts was that fossils originally came from living organisms. His other equally famous observations are often grouped together to form the laws of stratigraphy.

James Hutton and Charles Lyell also contributed to early understanding of the Earth's history. Their contributions included observations at Edinburgh in Scotland concerning angular unconformity in a rock face. In fact it was Lyell that influenced Charles Darwin greatly in his theory of evolution. Lyell influences included his belief (then speculative) that the present is the key to the past.

Hutton first proposed the theory of “uniformitarianism”. This is now a basic principle in all branches of geology. Hutton also supported the idea that the Earth was very old. This was in opposition to the prevailing concept of the time. The prevailing view was that the Earth had only been around a few millennia. Uniformitarianism describes an Earth which was created by the same natural phenomena remain at work today.

The prevailing concept of the 18th century in the West was that earth was very young, and its history had been dominated by catastrophic events. This view was strongly supported by adherents of Abrahamic religions. This belief was based largely on a literal interpretation of their religious scriptural passages. The concept of uniformitarianism met with considerable resistance and the catastrophism vs. gradualism debate of the 19th century resulted.

A variety of discoveries in the 20th century provided ample evidence that Earth history is a product of both gradual incremental processes and sudden cataclysmic events. Violent events such as meteorite impacts and large volcanic explosions do shape the Earth's surface. However this is in addition to gradual processes throughout earth's history such as weathering, erosion and deposition. The present is the key to the past, and it includes catastrophic as well as gradual processes.

SHIPPING & RETURNS/REFUNDS: We always ship books domestically (within the USA) via USPS INSURED media mail (“book rate”). Most international orders cost an additional $19.99 to $53.99 for an insured shipment in a heavily padded mailer. There is also a discount program which can cut postage costs by 50% to 75% if you’re buying about half-a-dozen books or more (5 kilos+). Our postage charges are as reasonable as USPS rates allow. ADDITIONAL PURCHASES do receive a VERY LARGE discount, typically about $5 per book (for each additional book after the first) so as to reward you for the economies of combined shipping/insurance costs.

Your purchase will ordinarily be shipped within 48 hours of payment. We package as well as anyone in the business, with lots of protective padding and containers. All of our shipments are fully insured against loss, and our shipping rates include the cost of this coverage (through stamps.com, Shipsaver.com, the USPS, UPS, or Fed-Ex). International tracking is provided free by the USPS for certain countries, other countries are at additional cost.

We do offer U.S. Postal Service Priority Mail, Registered Mail, and Express Mail for both international and domestic shipments, as well United Parcel Service (UPS) and Federal Express (Fed-Ex). Please ask for a rate quotation. Please note for international purchasers we will do everything we can to minimize your liability for VAT and/or duties. But we cannot assume any responsibility or liability for whatever taxes or duties may be levied on your purchase by the country of your residence. If you don’t like the tax and duty schemes your government imposes, please complain to them. We have no ability to influence or moderate your country’s tax/duty schemes.

If upon receipt of the item you are disappointed for any reason whatever, I offer a no questions asked 30-day return policy. Send it back, I will give you a complete refund of the purchase price; 1) less our original shipping/insurance costs, 2) less any non-refundable fees imposed by Please note that though they generally do, may not always refund payment processing fees on returns beyond a 30-day purchase window. So except for shipping costs and any payment processing fees not refunded by , we will refund all proceeds from the sale of a return item. Obviously we have no ability to influence, modify or waive policies.

ABOUT US: Prior to our retirement we used to travel to Eastern Europe and Central Asia several times a year seeking antique gemstones and jewelry from the globe’s most prolific gemstone producing and cutting centers. Most of the items we offer came from acquisitions we made in Eastern Europe, India, and from the Levant (Eastern Mediterranean/Near East) during these years from various institutions and dealers. Much of what we generate on Etsy, Amazon and goes to support worthy institutions in Europe and Asia connected with Anthropology and Archaeology. Though we have a collection of ancient coins numbering in the tens of thousands, our primary interests are ancient/antique jewelry and gemstones, a reflection of our academic backgrounds.

Though perhaps difficult to find in the USA, in Eastern Europe and Central Asia antique gemstones are commonly dismounted from old, broken settings – the gold reused – the gemstones recut and reset. Before these gorgeous antique gemstones are recut, we try to acquire the best of them in their original, antique, hand-finished state – most of them originally crafted a century or more ago. We believe that the work created by these long-gone master artisans is worth protecting and preserving rather than destroying this heritage of antique gemstones by recutting the original work out of existence. That by preserving their work, in a sense, we are preserving their lives and the legacy they left for modern times. Far better to appreciate their craft than to destroy it with modern cutting.

Not everyone agrees – fully 95% or more of the antique gemstones which come into these marketplaces are recut, and the heritage of the past lost. But if you agree with us that the past is worth protecting, and that past lives and the produce of those lives still matters today, consider buying an antique, hand cut, natural gemstone rather than one of the mass-produced machine cut (often synthetic or “lab produced”) gemstones which dominate the market today. We can set most any antique gemstone you purchase from us in your choice of styles and metals ranging from rings to pendants to earrings and bracelets; in sterling silver, 14kt solid gold, and 14kt gold fill. When you purchase from us, you can count on quick shipping and careful, secure packaging. We would be happy to provide you with a certificate/guarantee of authenticity for any item you purchase from us. There is a $3 fee for mailing under separate cover. I will always respond to every inquiry whether via email or message, so please feel free to write.

Under a Green Sky: Global Warming, the Mass Extinctions of the Past, and What Th

$23.23

The 6th Extinction: A Sigma Force Novel (Sigma Force, 10)

$19.68

Mass Extinction Permian Triassic Jurassic Cretaceous Clue Search Rivers in Time

$30.49