To the Moon and Back chapter sampler

The Emu in the Sky

third the size of Earth. Both were hot, turbulent places with molten rock mantles wrapped around ferocious dense cores of liquid iron. One day the two planets collided, spewing enough dust, rock and vapour into orbit to form a broad ring about 12,000 kilometres above Earth. The Moon was formed from the outer edge of the ring of dust and rock while the inner part of the ring fell back to Earth. The new ‘Moon’ then slowly swung further out into orbit about 380,000 kilometres from Earth — which is where it is now. How do we know? Why couldn’t the Moon have been formed from giant swirls of matter spat out by a madly turning early Earth? The answer is iron. When the two giant bodies collided their heavy molten iron cores melted together, while part of the rocky outer parts splashed out to make the Moon. So now 30 per cent of Earth is iron, but iron only makes up 2 per cent of the Moon. If the Moon had been made from the same material as the whole Earth, it would have a similar percentage of iron and other matter. It all probably happened very fast — a few hours for the two planets to collide, a few weeks for the present Earth to form from what had been two mini planets, with a ‘young Moon’ orbiting about 20,000 kilometres away. That ‘ancient Earth’ was still much smaller than our Earth is now. It took about 50 million years of more asteroid and meteor collisions to make Earth and the Moon the actual sizes they are now. The close presence of the Moon and

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