In the grand scheme of things, the entirety of human existence has barely lasted the blink of an eye. We’re freshmen in our own home and constantly learning—which is why our understanding of the universe changes by the day. One recent shakeup comes courtesy of scientists in Greenland, who have found traces of life dating back 3.7 billion years, pushing back life's earliest known appearance by hundreds of millions of years. They published their findings in the journal Nature

As any historian can tell you, reconstructing the past is a complicated and nuanced process, since all we have to go on is what’s been left behind. And the farther back in time you go, the harder it gets. Much of what we “know” about dinosaur behavior amounts to highly educated guesses based on footprints or the shape of a break in bone. Looking back even farther to the planet's earliest life forms, and you don’t even have bones or footprints to go on, since the simple organisms that gave rise to every living thing on Earth were both microscopic and squishy. To understand the world of these organisms—indeed, even to find them—researchers often have to rely on context clues.

One great indicator of microbe activity is mineral formations. Our earliest ancestors interacted with chemicals in their environments in ways that left behind solid, densely layered structures called stromatolites. Each stromatolite is kind of like an apartment building: a sturdy home that will be around long after the soft bodies within it have decayed and disappeared. The building is not its inhabitants, but without them, it would not exist. 

The oldest known stromatolites in the world are a series of dome- and cone-shaped structures in Western Australia. Experts estimate that these microbe-made lumps in the exposed red rock are about 3.48 billion years old.

But as our planet’s climate shifts and glaciers melt, new sections of primordial stone have come to light. One such section is in the Isua region of southwest Greenland, where scientists found stromatolites in a newly exposed outcrop of very, very old rock.

 
Itsy-bitsy microbe condos. Image credit: Nutman et al. in Nature.2016

The wave-shaped formations were small, ranging from one to four centimeters in height, but the layered structure within was unmistakable. The rock in which the waves were embedded is at least 3.7 billion years old—which makes these the oldest fossils on earth by a good 220 million years.

Experts say finding the stromatolites is a reminder of the tenacity of living things. “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,” wrote Abigail Allwood of NASA in an accompanying commentary. “Give life half an opportunity and it’ll run with it.”

[h/t Gizmodo]

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