Fossils recently discovered in Greenland contain evidence of the earliest known life on earth—dating to 3.7 billion years ago (bya), claim researchers who have been studying the finds. The minute, sedimentary remains, called stromatolites, of microbial colonies that grew on an ancient shoreline are described by a team of Australian researchers in a paper published this week (August 31) in Nature.
“The approximately 3.5-billion-year-old stromatolites in sedimentary rocks of Western Australia are currently regarded as the oldest evidence of life on Earth, and pushing the record further back in time had seemed unlikely because there is almost no rock remaining from the earliest period of Earth’s history,” writes Abigail Allwood of the California Institute of Technology in an accompanying commentary. In this extraordinarily rare find, researchers have done just that.
The fossils corroborate previous evidence from genetic molecular clocks that places the origin of life somewhere around 4 bya, the study’s authors note. However, the finding should be interpreted with caution, since “structures that look similar to stromatolites can form without the action of living organisms” and the study is “limited by the information available in the tiny outcrop,” Allwood observes.
To the untrained eye, the remarkable fossils don’t look like much. They consist of small, cone-shaped disturbances in metamorphic rock, which according to chemical and geological evidence were created by mats of microorganisms living in shallow seawater pools. As the primitive microorganisms grew over each other as if inhabiting ramshackle tenements, they left telltale sediment deposits that researchers can now identify and date. The team of scientists discovered the fossils in southwest Greenland, in rock newly exposed by melting snow.
“Earth’s surface 3.7 billion years ago was a tumultuous place, bombarded by asteroids and still in its formative stages,” Allwood writes. “If life could find a foothold here, and leave such an imprint that vestiges exist even though only a minuscule sliver of metamorphic rock is all that remains from that time, then life is not a fussy, reluctant and unlikely thing. Give life half an opportunity and it’ll run with it.”