Fossil Find Could Boost Hunt for Ancient Mars Life

Discovery of fossilized microbial life in a 3.7 billion-year-old Earth rock raises the prospect that Mars, which was not all that different from Earth at the time, might have had life too.

Image: Mosiac of the Yellowknife Bay area of Gale Grater taken by the NASA Mars rover Curiosity. Scientists found strong evidence of an ancient lake and stream deposits suggesting past environmental conditions suitable for microbial life. Credit: NASA/JPL/Caltech/MSSS The discovery of fossilized microbial life that is 220 million years older than anything previously found on Earth sweetens the prospect that life may have developed on Mars as well, which was not all that different from Earth at the time.

"Earth's surface 3.7 billion years ago was a tumultuous place, bombarded by asteroids and still in its formative stages," Abigail Allwood, an astrobiologist at NASA's Jet Propulsion Laboratory in Pasadena, Calif., wrote in a commentary published in this week's Nature.

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"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," Allwood wrote.

Allwood's essay accompanied research results , also published in Nature, from a team of Australian scientists who found evidence of life in Earth's oldest rocks, located in Greenland.

"These are not the kinds of rocks that palaeobiologists would consider a good prospect for signs of life, because they are not sedimentary like those that host most of Earth's fossil record. Rather, they are metamorphic, which means that they have been extensively deformed and altered by heat and pressure during deep burial," Allwood notes.

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Allen Nutman, a researcher at the University of Wollongong in Australia, and colleagues came across what Allwood describes as "a rarity" in Greenland's Isua Greenstone Belt.

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"In a small area newly revealed by snow melt, they found relatively well preserved rocks that have survived geological time with some of their original sedimentary attributes intact. In this tiny window into the deep past are subtle geochemical and textural clues to an ancient surface environment that is surprisingly familiar as a habitat for life.

"Within the rocks can be seen ancient ripple marks and piles of rock fragments deposited during an ancient storm. Combined with seawater-derived mineral chemistry, these features all point to a shallow marine, carbonate, mineral-depositing environment similar to those that have hosted abundant biota throughout Earth's history," Allwood said.

Setting back the clock for when life arose on Earth boosts the odds that Mars too had what it needed for life to take hold.

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"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. Suddenly, Mars may look even more promising than before as a potential abode for past life," Allwood wrote.

Several Mars missions have shown that around the time that the Isua rocks were forming, "Mars did not look too different from Earth from a habitability perspective, with standing bodies of water at the surface," she added.

Given that the era of the late heavy asteroid bombardment in the solar system had just ended, scientists are unsure if Mars' window for life was open long enough before its water dried up.

"We have only one example of life with which to address this," Allwood concluded. "If the Isua structures are indeed microbial, then that example says 'yes.'"