ImagingGeek,
Revisiting your earlier reply to my stating that you were assuming the Earth’s surface gravity could not have changed, you stated that:
“It's not an assumption; I provided two papers - one analyzing paleomagnetic data, the other tidal sediments - to measure the mass of the earth over its history. They clearly showed there has been no change in the earths mass.”
I would agree that the Earth’s total mass has not changed significantly over the last few hundred million years. However you, and most people, don’t realize that there is another mechanism that could alter the surface gravity on the Earth. That method is the shifting of the Earth’s cores, either or both.
The Gravity Theory of Mass Extinction explains this. For hundreds of millions of years, continental land masses have formed various land mass configurations, quite different from today’s fairly balanced widespread distribution. Since the Earth is spinning, any unbalanced distribution of these land masses as in the case of Pangea, according to the theory, causes the core(s) to shift away from the center of mass of the consolidated land masses lowering the surface gravity on it. As Pangea broke apart and dispersed, the reverse process would increase surface gravity until the core(s) returned to their central position.
While its a nice theory, the math doesn't stand up in two different ways. The first thing you need to remember is the earths mass is constant, regardless of the position of the core(s). As such, when viewed from a distance the total gravity of the earth will always be constant. What
can vary is the distribution of that mass, and thus there can be small variations in the gravitational force at different points on the earths surface. In fact, there are satellites which map the ocean bottom using these small gravitational differences.
Lets take the case of
unshifted cores first. In this case you would have additional mass on one side of the planet (in the form of pangea), and thus pangea would have a high surface gravity than the earth's average. But how much different? Lets assume:
1)
ALL continental mass is located in pangea, accounting for 30% (0.3) the total of earths surface area.
2) That the continental crust averages 40km thick, and the oceanic crust averages 8km
3) That the earths crust is 1% the total mass of the earth
4) That the density of the crust is the same throughout (the oceanic crust is actually more dense)
5) That the crust and the mantle/core are of the same density (also false; the crust is less dense)
Note: these numbers are from
wikipedia.So pangea would weight .3*40 = 12 units (unit being fractions of a km
3)
The ocean would weigh .7*8 = 5.6 units
For a total crustal "mass" of 12+5.6 = 17.6 units
So the weight of the 2 crusts, relative to the mass of the earth is:
pangea = (12/17.6)*.01 = 0.006818 (0.7%) the earths total mass
ocean = (5.6/17.6)*.01 = 0.0031818 (0.3%) the earths total mass
Two more assumptions, to make the math easy:
1) This differential mass distributed over an equivalent area on each side of the globe, and the ocean/continents are distributed opposite each other. This allows us to treat them as point masses resting on the surface of the mantle, on opposite sides of the equator. It makes the math easier, but exaggerates the gravitational differences.
2) We have a constant radius. Given the small difference in crustal thickness vs. oceanic thickness (relative to the whole earth), this is reality, rather than an assumption, to within a few thousandths of a percent.
Given a constant radius, gravity scales linearly with mass (Fg = GM/r
2, r being constant). Ergo, in this unbalanced case there would be ~0.4% more gravity on pangea side compared to the ocean side.
0.4% isn't going to account for much - its but a tiny fraction of the forces a flying organisms would experience due to air currents, wind gusts, and the like. In the case of Diplodocus (who had a mass of ~50 tonnes, i.e. 50,000kg), it would be equivalent to an extra 200kg. To put that into context, for an average human (60kg) that would be 210 grams (~0.5 lb); about the weight you gain drinking one cup of coffee.
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Now, what about a shifting core? Once again, I would remind you that the earths mass, and thus total gravity, is constant. As such, all that can happen is the relative amounts of gravity felt on specific points of the surface can change.
In the case of a shifting core, it is going to shift to
correct an inequity in the earths mass - i.e. it'll shift away from pangea. This will
reduce the gravity felt on pangea and
increase the gravity felt in the oceans. Assuming equilibrium is met (i.e. the earths center of mass is returned to its center of rotation), and the earth remains spherical, the gravity on the surface will be
equalized - as in pangea will experience exactly 1.0G, and the ocean side will experience 1.0G. Or, in other words, the tiny gravitational distortion formed by the thicker crust on the pangea side will be eliminated. I.E. Diplodocus can have a Diplodocus-sized coffee without consiquence.
Bryan
