Dating back to the precambrian era
Resources and references * Dates from the International Commission on Stratigraphy's International Stratigraphic Chart, 2009. Speer created the original Archean page, 3/9/1997; Ben M.
This most likely happened prior to 3.8 billion years, but hard evidence for this is lacking.
The Archean eon, which preceded the Proterozoic eon, spanned about 1.5 billion years and is subdivided into four eras: the Neoarchean (2.8 to 2.5 billion years ago), Mesoarchean (3.2 to 2.8 billion years ago), Paleoarchean (3.6 to 3.2 billion years ago), and Eoarchean (4 to 3.6 billion years ago).* If you were able to travel back to visit the Earth during the Archean, you would likely not recognize it as the same planet we inhabit today.
The atmosphere was very different from what we breathe today; at that time, it was likely a reducing atmosphere of methane, ammonia, and other gases which would be toxic to most life on our planet today.
Surrounding particles began to coalesce by gravity into larger lumps, or planetesimals, which continued to aggregate into planets.
"Left-over" material formed asteroids and comets, like asteroid Ida, above right.
Heavier elements are generated within stars by nuclear fusion of hydrogen, and are otherwise uncommon.