Final answer:
Earliest unverified evidence of life dates as far back as 4.1 billion years, while more solid evidence such as stromatolites is found at 3.5 to 3.95 billion years ago.
Explanation:
The earliest unverified evidence of life on Earth exists in the form of geochemical signatures and 'possible' microbial remains that date as far back as 4.1 billion years ago, near the end of the Hadean Eon. More solid geological evidence, such as the presence of stromatolite formations, dates to between 3.5 and 3.95 billion years ago during the Archaean Eon. The appearance of the first actual cells on Earth had to contend with a non-reducing environment, according to the traces left in ancient rocks and fossils, though the exact pathway to the origin of life remains uncertain.
These traces include graphite deposits and stromatolites, the latter being complex structures built by microbial communities that still exist today. The record for life's earliest beginnings is scarce because Earth's crust is constantly changing, which has either erased or deeply buried the evidence in its ancient terrain. Most of the direct evidence available through fossils has been preserved only in the past 600 million years, but geochemical data points to the possibility of life existing on Earth for most of its history.