Why is The Earth not shaped like an apple with a bite taken out of it?

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Offline John Chapman

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According to my second most favourite non-porn site, wikipedia, our Moon was formed as the result of a large impact between between the Earth and another planet/asteroid/chunky thing. If that is so why has the planet Earth not got a moon-sized chunk knocked out of it? Come to that, why isn't the moon a corresponding irregular shape?

In other words why are the Earth and Moon both round?
« Last Edit: 22/02/2009 19:16:16 by John Chapman »

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Offline RD

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'cos the Earth was (and still is) mostly liquid, (outer core and mantle)...


[attachment=7072]

http://en.wikipedia.org/wiki/Structure_of_the_Earth
« Last Edit: 22/02/2009 18:02:08 by RD »

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Offline LeeE

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Once a body becomes large enough gravity pulls the body in to a spherical shape.  It's also probable that both the Earth and the planetesimal that collided with it, resulting in the Moon, were largely still molten when the collision occurred.  In any case, the collision would have produced a lot of heat and probably melted anything that had already solidified.

Even today, the Earth is still mostly molten, with just a relatively thin crust of solid material on it's surface (Much of the magma isn't really fluid, but it's not solid either - perhaps one of our geologists will step in here for a fuller explanation).
...And its claws are as big as cups, and for some reason it's got a tremendous fear of stamps! And Mrs Doyle was telling me it's got magnets on its tail, so if you're made out of metal it can attach itself to you! And instead of a mouth it's got four arses!

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Offline John Chapman

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Thanks Lee

I was just about to ask RD what he meant when he said the Earth is still liquid but I think you've just covered that point.

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Offline RD

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If you want a fruity comparison, the Earth is a bit like a tangerine: it is an oblate spheroid.
Rotation makes it bulge a little at the equator and a little flat at the poles.
« Last Edit: 22/02/2009 18:08:53 by RD »