17 March 2008

Under Pressure: Earth Science

By Rusty Rockets

Supervolcanoes, abrupt climate change, magnetic field reversals and other potential planetary pitfalls are good fodder for disaster movies, but could they really happen? It may be that the best way to answer that question and anticipate potentially disastrous changes in Earth's processes is to delve into our planet's history. By understanding our planet's past, we may be able to predict when the Earth is about to unleash a major catastrophe.

Now, a bunch of United States government agencies and scientific departments have encouraged leading Earth science boffins to bang their heads together to identify the 10 most pressing Earth science questions of the 21st century. This sobering request resulted in the following list (in no particular order) released in a new report by the National Research Council (NRC).

How did the Earth form?

You may be excused for thinking that scientists already know the answer to this question, but this is not the case. In the NRC report, entitled "Origin And Evolution Of Earth: Research Questions For A Changing Planet," the authors write that while there may be a consensus among scientists that our solar system's sun and planets came from the same nebular cloud, their knowledge of how Earth acquired its chemical composition is limited. According to the NRC report's authors, this knowledge deficit makes it difficult to produce any confident claims regarding Earth's evolution, or why other planets differ from one another.

Developments in this area are ongoing and Christopher Johns-Krull, assistant professor of physics and astronomy at Rice University, may have just this week discovered an important clue as to how Earth-like planets do form. Johns-Krull and his team have identified the first evidence yet of tiny, sandy particles orbiting a distant newborn solar system at roughly the same distance as the Earth orbits the sun.

"Precisely how and when planets form is an open question," he said. "We believe the disk-shaped clouds of dust around newly formed stars condense, forming microscopic grains of sand that eventually go on to become pebbles, boulders and whole planets."

Johns-Krull considers this an important step toward unlocking the mysteries of planet formation. "It's very exciting because it opens up so many doors for new types of research on this disk." Which is exactly what the recent NRC report is all about: opening up new lines of investigation regarding Earth's planetary history.

What happened during Earth's "dark age" (the first 500 million years)?

Given what little scientists know, or could ever know, about this period, this question may never be answered. The NRC report refers to the claim that during this period another planet collided with the Earth during the latter stage of its formation. Scientists have further deduced that this collision not only caused Earth to melt down to its core, but also created the debris that would eventually become the moon.

While the NRC report states that this "dark age" is critical to understanding Earth's evolution, researchers will be hampered by the fact that there is little to go on, as many of the rocks comprising Earth's crust were formed less than 100 million years ago.  

How did life begin?

The question of how life began (abiogenesis) is the big question that has had scientists racking their brains for years, with many models being produced, but no definitive one. Creationists often take great pleasure in pointing this out to evolutionists, even though most scientists consider abiogenesis and evolution separate areas of research, and a lack in one does not signify a corresponding lack in the other.

Of all the ten questions posited, this question has probably generated the most imaginative and outlandish of suggestions - be it god, aliens, or the idea that we are all just the imaginings of another being. Thankfully, we don't have to rely upon spectacular leaps in logic in regard to the origin of life, as scientists have proposed a number of plausible explanations based on sound geological and biological knowledge.

But again, while researchers have the investigative tools required, part of the problem with producing a viable explanation for life stems from the fact that there is scant evidence available. Needless to say, this makes working out what the conditions were like on Earth when life first began extremely difficult. The NRC report states that the only remaining evidence of the conditions that generated life's inception is to be found by analyzing rocks and minerals, or on Mars, where its sedimentary record of evolution predates the oldest rocks on Earth.

One of the more novel suggestions comes from American chemist and biologist Stanley Miller (of the famed Miller-Urey experiment in the 50s, which created amino acids by exposing inorganic chemicals to UV radiation), who claims that life was not the result of heat, as many think, but rather ice. In 1997, Miller began defrosting a 25-year-old ammonia and cyanide-filled vial that had been kept at a temperature matching that of Jupiter's moon Europa. Amazingly, and contrary to all assumptions, Miller discovered that the concoction in the vial now contained the familiar signs of complex polymers made up of organic molecules. Since then, further evidence supporting Miller's on-the-rocks hypothesis has come to light.

Despite our ingrained vision of a steaming, primordial, life-producing goop, scientists have gradually come around to the idea that, chemically speaking, ice is a better candidate for abiogenesis. They've noted, perhaps counterintuitively, that while heat instigates chemical reactions, reactions within ice can be sped up significantly. Even at temperatures of -60 Fahrenheit, tiny compartments of liquid water can become trapped inside ice, and this liquid water can contain simple molecules like the ones Miller used in his experiment. But the amazing part is that the chemical reactions between these molecules are accelerated due to the immense pressure created within these miniscule ice compartments. Later tests showed that Miller's 25-year-long experiment had indeed produced the building blocks of life.

Tragically, Miller's research career ended after he suffered a debilitating stroke in 2002 (followed by his death in 2007), which resulted in a variety of his long- to short-term lab experiments being trashed to make way for building renovations. Miller's legacy lives on, however, as researchers have now widened their search for life to include icy locales like Jupiter's moon Europa.  

How does Earth's interior work, and how does it affect the surface?

Most of us probably remember the colorful charts depicting Earth's interior, which, disappointingly, showed no sign whatsoever of a subterranean world filled with giant mushrooms and dinosaurs. If you were even more observant you may also have noted the convection arrows on these charts, which depict the constant convective motion of the Earth's mantle and core. According to the NRC report, core convection produces Earth's magnetic field, which may also lead to the influence of surface conditions. Likewise, mantle convection is also suspected to influence surface conditions that lead to phenomena such as seafloor generation, volcanism, and the creation of mountains.

But as this question is in the top ten, you've probably already guessed that there is much more to learn. In fact, scientists don't really know how to accurately model Earth's inner motions, let alone calculate how these motions worked during Earth's early history. Contrary to early speculation, seismologists have revealed that the Earth's interior is "messy" rather than consistently uniform. It's also been suggested that because the core is not firmly connected to the mantle that it may rotate a little faster or slower than the rest of the Earth.

Who knows; perhaps the Earth acts like a giant gyroscope. But whatever the answer, currently scientists do not have a reliable model of Earth's interior convective motions, which makes it nigh on impossible to predict how they affect its surface.

Can earthquakes, volcanic eruptions, and their consequences be predicted?

"Only fools and charlatans predict earthquakes," said Charles Richter, the inventor of the Richter scale (a measurement, not a device, as is sometimes thought).

The authors of the NRC report state that while there has been some progress made in calculating the probability of earthquakes, the ability to make short-term predictions regarding the exact time and place an earthquake will hit is unlikely. Adding: "even if short-term earthquake prediction ever became a reality, it would still be impossible to protect most of the built environment from damage." But Charles Richter (who suffered from Asperger's Syndrome) was nothing if not pragmatic: "Aid [for research] is given to people who would like to forget that for public safety we do not need prediction. Earthquake risk could be removed, almost completely, by proper building construction and regulation," he sagely noted.

But all of this paints a rather bleak picture regarding research into earthquakes and volcanic eruptions. The NRC report states that geologists have made some significant advances with regard to finding out how ruptures begin and end, and the intensity of shaking that characteristically accompanies such seismic shifts. Researchers' predictive capabilities involving volcanoes are also improving, but are continually confounded when they try to model the movement of magma.

The NRC report draws attention to the successful prediction of the eruption of Mount Pinatubo, in the Philippines, which led to an evacuation of the areas most in danger. However, researchers warn that what they learned from this particular case may not be applicable to other volcanoes. "Much larger volcanic systems such as Yellowstone have shown signs of restlessness that could, at some point, portend an impending eruption," write the researchers. "We do not know whether we can accurately scale up modern instrumental data for Pinatubo-sized eruptions to anticipate events that may be 100 or 1,000 times larger."

From this list of five questions alone it's obvious that Earth scientists have their work cut out for them. In the follow-up article we'll look at the other five questions that Earth scientists must face this century, which will hopefully lead to the protection of the planet, its complex systems, and, in turn, the life that inhabits it.

Under Pressure: Earth Science Part (II)
Did Civilization Emerge Thanks To A Change In The Weather?
Volcano Study Suggests Bronze Age History Needs Rewrite
Going Gaga Over Gaia
Increasing Soil Erosion Threatens World's Food Supply
Mountains Formed In The Blink Of An Eye