For How Long Has There Been Life On Earth at Life

For How Long Has There Been Life On Earth. ~3.5 bya (billion years ago). The best guess is somewhere between 3.5 and 4 billion years, with the earliest.

For about how many years of geological time have humans existed on earth? For what percentage of time (of the 3.5 billion years that there has been life on earth) were prokaryotes the only living organisms? How long has there been life on earth?

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~3.5 bya (billion years ago). Fossils have even taught us about the climate of the earth long ago. Fossils have taught us how and when rock layers have formed. The period of earth's history that began 2.5 billion years ago and ended 544 million years ago is known as the proterozoic.