Scientists have just unearthed what they claim to be the oldest fossils ever found on our planet. They're so ancient they predate the next oldest finds by roughly a quarter-billion years.

These newly uncovered fossils are 3.7-billion-year -old traces of ancient microbes, and were found under recently melted perennial snow in southwest Greenland. The fossils were discovered by a team of geologists and paleontologists led by Allen Nutman at the University of Wollongong in Australia. Nutman and his colleagues outlined their fossil discoveries today in the journal Nature.

"Give life half an opportunity and it'll run with it."

Nutman's fossils are a breathtaking find for reasons beyond their unparalled age. "If these are really the figurative tombstones of our earliest ancestors, the implications are staggering," writes Abigail Allwood, an earth scientist at NASA's Jet Propulsion Laboratory, in an essay accompanying the science paper.

That's because the fossils are tentative proof that life formed very quickly after a violent and chaotic era in our planet's history—a period of intense asteroid shelling called the Late Heavy Bombardment that ended 3.8 billion years ago. "If life could find a foothold here, and leave such an imprint that vestiges exist even though only a minuscule sliver of [rock] is all that remains from that time, then life is not a fussy, reluctant and unlikely thing," Allwood writes. "Give life half an opportunity and it'll run with it."

Allen Nutman (left) and Vickie Bennet (right) with a specimen of 3.7-billion-year-old stromatolites from Isua, Greenland. Yuri Amelin

Microbe Fossils

If you didn't know what to look for, you'd probably glance right past these new fossils without ever noticing them. To the untrained eye they look like little more than wavy patterns embedded in rock, almost like a minuscule etching of a mountain range. But these inch-high patterns are called stromatolites, and are the fossil fingerprints of Earth's early microbes. Colonies of minuscule microbes lived and died by the trillions, leaving a faint footprint over tens of thousands of years in the form of these ridgelike patterns in rock and sediment.

After studying the chemistry and structure of the fossils, Nutman's team believes they were created in primordial pools or shores of seawater. Today, they are locked away in hard metamorphic rock—particularly, a 3.7-billion-year-old belt of stone called the Isua Greenstone Belt.

Identifying stromatolites is a fairly hard task, and even now with their study published, Nutman and his colleagues urge great caution and skepticism. "The problem is that structures that look similar to stromatolites can form without the action of living organisms," Allwood writes, and within today's fossils "there are no organic or cellular remains."

"The problem is that structures that look similar to stromatolites can form without the action of living organisms."

But Nutman's team is still confident their fossils are the real deal thanks to an intense study of the internal structure and chemistry of the rocky finds. For example, the fossils contain significant traces of a low-temperature flavor of the mineral dolomite, an almost certain fingerprint of microbial activity.

Life Next Door

Allwood says these new fossils may help scientists revise our estimate of how often (if at all) life has arisen outside of Earth. Even more tantalizingly, they might point to undiscovered remains of life on Mars.

"Our understanding of the nature of life in the universe is shaped by how long it took for Earth to establish the planetary conditions for life," she writes. If life sprung up rapidly during Earth's cool-down phase after its last major session of asteroid shelling, then "suddenly, Mars may look even more promising than before, as a potential abode for past life. A plethora of Mars missions has shown that around the time that [the fossils in today's Greenland] rocks were forming, Mars did not look too different from Earth from a habitability perspective, with standing bodies of water at the surface."

"But as habitable as those waters may have been, the question is, did they dry up well before any ingredients for life could give rise to living organisms?" asks Allwood. If today's fossils are indeed the remains of rapidly-developing microbes, then that answer could very well be yes.

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