What Earth's oldest fossils could mean in the search for extraterrestrial life

Is there (or was there ever) life on Mars? Europa? Enceladus?

New studies and theories delve deeper and deeper into possibilities of ancient life anywhere outside of our planet. What could have once been habitable conditions are often inferred from telescope images and specimens brought back by spacecraft — but this time, researchers didn't have to look very far for a potential link to something out there.

Recently, a research team investigating antediluvian life discovered fossils of microorganisms that are relics of what may have been the oldest life-forms to ever crawl on Earth. Their findings were published in the latest volume of Nature. Remnants of these iron-eating microbes are thought to be anywhere from 3.8-4.3 billion years old and originated around hydrothermal vents at the bottom of the ocean.

Embedded in a rare sample of sedimentary rock from the oceanic crust, they were found to mirror the stromatolites that still exist around similar undersea vents that gush heat vital for their survival. The fossils' structure and location are now telling scientists where to look for evidence of anything that might have lived, and might still live, elsewhere in our solar system.

"We know how to turn life on Earth into a testable hypothesis," said astrobiologist Shawn Domagal-Goldman of NASA's Goddard Space Flight Center. "The best-known alien biosphere for which we have data is Archean Earth, the ancient Earth. We now can start to understand how we would look for the signs of life that would have been present on Archean Earth, when there was no oxygen in the atmosphere."

An iron-rich stromatolite fossil similar to the ones the fossilized microbes were found in. 

Archaean Earth is the closest thing to an alien biosphere that we can study without launching something into space. While scientists still haven't been able to confirm when or where life on Earth emerged, the fossil find suggests that hydrothermal vents are a likely candidate. This opens the portal to potential life or evidence of life on worlds other than our own, at least from the point of view of the Gaian model.

Narrow as the parameters for life on Earth may be when considering the vast expanse of space, what we know about the conditions necessary for life here is really the only mirror we have for comparison at the moment. We are still in the dark as to whether things ever existed (or still exist) that thrive off toxic alien atmospheres.

With what they now know about life roughly 10 billion years plus several hundred thousand after the Big Bang (when our planet is believed to have formed), scientists will at least have guidelines, albeit Gaian guidelines, for exploring other planets for traces of alien microbes. Jupiter's moon Europa has recently been spotlighted for its ice volcanoes that are believed to spew freezing saltwater slush. Europa and Saturn's moon Enceladus are both thought to be hiding vast oceans beneath thick icy crusts.

And Mars is the obvious one. Scientists have been constantly scouring the Red Planet for signs of life, and both rock formations on its surface and the chemical composition of those rocks have led them to believe it could have once had Earth-like conditions. The fossil discovery is just one more thing to take into consideration when launching the Mars 2020 rover.

"While there is no assumption that life beyond Earth, if it exists, would be the same as terrestrial life," acknowledges Domagal-Goldman, "It's a starting point."

(via Space.com)

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