The Oldest Fossils Ever Found Date Back 3.7 Billion Years
Earth was down to host life even in its tumultuous infancy.
The oldest fossils in the entire goddamn record have been found in Greenland's Isua Greenstone Belt, according to new research published Wednesday in the journal Nature. These fossils advance our understanding of how and when life formed on our planet, and the role it played in shaping the planet's biosphere.
Forged by cyanobacteria some 3.7 billion years ago, these layered sedimentary formations, called "stromatolites," push the timeline of confirmed life on Earth back by a full 220 million years. The previous record-holder, the well-known 3.5-billion-year-old stromatolites of Western Australia, has now been unseated by a wide temporal margin.
These newest oldest stromatolites, found embedded in the metamorphic Isua belt in southwestern Greenland, are incredibly subtle. The structures consist of conical waves of sediment deposited by ancient microbes for protection and shelter in shallow water environments.
Even the study's authors, led by geologist Allen Nutman of the University of Wollongong in Australia, admit that there's a chance that they might have been created by non-biological processes. But there are a few telltale hints, including the shape and chemical distribution of the structures, that likely "rule out an abiogenic origin," according to the team.
Provided that this assumption is vindicated by future research, the Isua stromatolites present the most distant glimpse into the origins of life on Earth in history.
"The discovery gives a snapshot of a single environment in which life existed at that time," Nutman told me. "We can now say that life populated shallow water settings, but we have no idea of how diverse other habitats were."
One of the most interesting wrinkles in this tale of discovery is the role of climate change in exposing the stromatolites to present-day researchers. Snow patches that were once perennial have been rapidly melting all over the Arctic, and Greenland is no exception. The Isua stromatolites were found under one of these normally snow-covered areas.
"We have actually made some other new findings from under other 'disappeared' snow patches, but in this case not related to early life," said Nutman. "These concern extra information on the ancient environment, and we plan to publish within the next year."
It's interesting that the most extreme window to date into life's origins was catalyzed by the shifting landscapes of our new Anthropocene era. But, as highlighted by an accompanying Nature article by Abigail C. Allwood, a field geologist at NASA's Jet Propulsion Laboratory, these early lifeforms are a reminder that life on Earth has weathered some tough challenges.
"If these are really the figurative tombstones of our earliest ancestors, the implications are staggering," Allwood said. "Earth's surface 3.7 billion years ago was a tumultuous place, bombarded by asteroids and still in its formative stages. 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."
Or, to put it in Jurassic Park terms, life finds a way—even in the Earth's rocky infancy, nearly four billion years ago, to say nothing of the countless worlds beyond it.