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The giant-impact hypothesis, sometimes called the Big Splash, or the Theia Impact suggests that the Moon formed out of the debris left over from a collision between Earth and an astronomical body the size of Mars, approximately 4.5 billion years ago, in the Hadean eon
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The Precambrian Era comprises all of geologic time prior to 600 million years ago. It is now known that life on Earth began by the early Archean and that fossilized organisms became more and more abundant throughout Precambrian time.
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A microscopic single-celled organism that has neither a distinct nucleus with a membrane nor other specialized organelles. Prokaryotes include the bacteria and cyanobacteria.
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Cyanobacteria or blue-green algae became the first microbes to produce oxygen by photosynthesis, perhaps as long ago as 3.5 billion years ago and certainly by 2.7 billion years ago. But, mysteriously, there was a long lag time – hundreds of millions of years – before Earth’s atmosphere first gained significant amounts oxygen, some 2.4 billion to 2.3 billion years ago.
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Eukaryotes are organisms with a nucleus. The oldest evidence of eukaryotes is from 2.7 billion years ago. Scientists believe that a nucleus and other organelles inside a eukaryotic cell formed when one prokaryotic organism engulfed another, which then lived inside and contributed to the functioning of its host.
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The first animals known to swim using muscles instead of drifting with the whims of the waves. The oldest ancestors of modern day jellies lived at least 500 million years ago, and maybe as long as 700 million years ago.
