Over at Download the Universe, Ars Technica science editor John Timmer reviews a science ebook whose science leaves something to be desired. Written by J. Marvin Herndon, a physicist, Indivisible Earth presents an alternate theory that ostensibly competes with plate tectonics. Instead of Earth having a molten core and a moveable crust, Herndon proposes that this planet began its existence as the core of a gas giant, like Jupiter or Saturn. Somehow, Earth lost its thick layer of gas and the small, dense core expanded, cracking as it grew into the continents we know today. What most people think are continental plate boundaries are, to Herndon, simply seams where bits of planet ripped apart from one another.
The problem is that Herndon doesn't offer a lot of evidence to support this idea.
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Once the Earth was at the center of a gas giant, Herndon thinks the intense pressure of the massive atmosphere compressed the gas giant's rocky core so that it shrunk to the point where its surface was completely covered by what we now call continental plates. In other words, the entire surface of our present planet was once much smaller, and all land mass.
I did a back-of-the-envelope calculation of this, figuring out the radius of a sphere that would have the same surface area as our current land mass. It was only half the planet's present size. Using that radius to calculate the sphere's volume, it's possible to figure out the density (assuming a roughly current mass). That produced a figure six times higher than the Earth's current density — and about three times that of pure lead.