"In just 200 million years, possibly less, the Earth was essentially formed, though still molten and subject to constant bombardment from all the debri that remained floating about.

At this point, about 4.4 billion years ago, an object the size of mars crashed into the Earth, blowing out enough material to form a companion sphere, the moon...

When the Earth was only about a third of its eventual size, it was probably already beginning to form an atmosphere, mostly of carbon dioxide, nitrogen, methane and sulphur. Hardly the sort of stuff that we would associate with life, and yet from this noxious stew life formed."

Bryson, Bill (2005) A Short History of Nearly Everything: Special Illustrated Edition. Random House, New York.