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Rare Earth

John on April 12, 2009 at 2:16 pm

From Live Science. Not a bad piece for Easter:

“The most impressive attribute of the Earth is the existence and amount of liquid water on its surface,” said Geoffrey Marcy, an astronomer at the University of California, Berkeley who has helped discover dozens of extrasolar planets. No one knows why Earth has the exact amount of water it does, which is relatively small considering that water molecules outnumber silicate molecules in the galaxy, he said…

Our planet’s Goldilocks-like “just right” location in the solar system has helped, as has its system of plate tectonics — the slip-sliding movements of Earth’s crust that are thought to have created the planet’s towering mountain ranges and plummeting ocean depths.

“The fact that Earth has plate tectonics allows for the carbon-silicate cycle to operate over geological timescales,” Valencia said. “With the carbon-silicate cycle, the levels of carbon in the atmosphere get regulated to keep the surface temperature around that of liquid water.”

Plate tectonics and water are inextricably linked. Not only does plate tectonics enable liquid water to exist by way of regulating the temperature, but many scientists have argued water enables plate tectonics to happen…

Life on Earth may also owe a debt to our nearest celestial neighbor, the moon.

Earth’s moon stabilizes our planet’s rotation, preventing drastic movements of the poles that could cause massive changes in climate that some scientists think could have doomed any chance for budding life to form or evolve.

The moon also helpfully pulls the ocean’s tides, which scientists suggest might have been the perfect place for early life to begin evolving to survive on land.

What the article doesn’t mention is that Earth’s plate tectonics and carbon cycle — necessary for maintaing the temperature of the earth as the sun brightened over the last four billion years — are directly tied to the existence of the moon.

The reigning paradigm is that very early in Earth’s history a large planet, something about the size of Mars, had a glancing collision with Earth. This sent most of Earth’s light weight material into orbit where it eventually coalesced into the Moon. Had this one-in-a-million collision not taken place, the Earth’s crust would be far too thick for plate tectonics to happen. As a result the planet would have no mountain building and no carbon cycle. You can watch a video visualizing the event here.

Additionally, most of the heavy core of the other planet settled into our Earth. One likely result is that we have a very heavy element rich core, the rotation of which produces a tremendous magentic field that shields us from the worst of the solar wind.

Even if we find a million Earth-like planets, the chances are they will be like what our Earth would have been if not for this one in a million collision that created the moon. Apart from this unlikely disaster, the chance of life surviving here (even if it began) would be very small.

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