Hadean The first geologic eon began with the formation of the Earth about 4,600 million years ago and ended 4,000 million years ago.
Thermal Genesis More broadly: abiogenesis - the natural process by which life arises from simple organic compounds. The earliest life on Earth existed at least 3,500 million years ago, at the beginning of the Archean Eon when sufficient crust had solidified following the molten Hadean Eon
Cambrian First geologic period of the Paleozoic Era, lasting from 541 to 485 million years ago. Although complex, multicellular organisms gradually became more common in the millions of years immediately preceding the Cambrian, it was during the Cambrian that life exploded, rapidly diversifying and producing the first representatives of many modern phyla, However, while diverse life forms prospered in the oceans, the land was comparatively barren.
Devonian A geologic period of the Paleozoic Era that occurred from 419 to 358 million years ago. This was the first significant adaptive radiation of terrestrial life.