Enlarge / One set of the possible stromatolites—with two slices cut out by the researchers. (credit: Allen Nutman)
In the history of life on Earth, the first chapter is still the most incomplete—and any good epic needs its origin story. The problem with finding that story is preservation. The earliest lifeforms were microscopic sacks of organic chemistry, so finding evidence for them, as far as needles in haystacks go, is not exactly equivalent to spotting a six-foot Apatosaurus bone. To make matters worse, most of the haystack has been burned to a crisp by geology since then.
Fossil evidence goes back about 3.5 billion years, with controversial isotopic signs that might signify life about 3.8 billion years ago (or perhaps even earlier). At this age, you run out of rocks. Although the planet is about 4.5 billion years old, very few rocks have survived for more than 3.5 billion years. The ones that have look their age, metamorphosed so much over the eons that signs of life might have been erased.
Still, the quest to push back the earliest evidence for life goes on. New finds are subject to rigorous debate, and researchers have to work hard to figure out whether a physical process could be responsible for a feature that has the appearance of a fossil.
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Source: Ars Technica – New find might be oldest evidence of life on Earth