Fossils for Earliest Life on Earth Found

The microbial fossil found in Greenland dates back an estimated 3.7 billion years.

Earth's oldest known fossils, dating to 3.7 billion years ago, have just been found in Greenland, according to a new study that not only reveals information about our planet, but also strengthens the possibility that Mars once harbored life.

The fossils -- microbial formations within rock revealed after a snow melt in Isua, southwest Greenland -- predate the prior earliest fossil evidence for life on Earth by 220 million years, according to the study that is published in the journal Nature.

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Since the microbial formations, known as stromatolites, indicate that communities of microbes had already formed by 3.7 billion years ago, it is likely that life on our planet began even before that very early date. Previous genetic molecular clock studies point to such a time as well.

Lead author Allen Nutman and his team further believe that there was "rapid emergence of life."

"'Rapid' stems from stromatolites being the products of communities, meaning that life had already been around for a geologically long time," Nutman, a professor of earth and environmental sciences at the University of Wollongong, explained to Discovery News.

"This places the origin of life in the Hadean (> 4 billion years), meaning that once conditions were suitable for life to appear on Earth (<4.2 or 4.3 billion years), the stages from pre-biotic organized molecules, through an RNA world to a DNA world, must, at least from the geological perspective, have been early and rapid."

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Several lines of evidence indicate that the stromatolites were formed by live organisms, according to Nutman and his team, who conducted the research with funding from the Australian Research Council. The evidence is based on prior knowledge of other existing stromatolites and their tell-tale characteristics.

For example, the structures have a conical shape and internal layering. Such contrasting composition and texture in the bounds of conical formations within rock "are fairly credible hallmarks of microbial activity," Abigail Allwood, a scientist at the Jet Propulsion Laboratory at the California Institute of Technology who did not work on the new study, wrote in an accompanying Nature article. She added that this type of layering, as well as the shape and texture of the structures, means that they are not just folded rock.

Concentrations of titanium and potassium are higher in the structures than between them, providing evidence that a different type of sediment had accumulated there. This is also a characteristic associated with other stromatolites.

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As for what type of microbe could have produced the stromatolites, its precise identity is unknown at this point.

"Beyond that stromatolites are microbial constructs, there is no evidence of what the culprits looked like beyond that they would have been single cellular," Nutman said, adding that he and his colleagues have already begun additional sulfur isotope testing to determine if there are signatures for metabolic (physical and chemical processes) present in the stromatolites. The results of those studies may reveal more about the likely microbes.

As it stands, the sedimentary inter-layered structures reveal that the microbes existed in a shallow water setting.

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"All that can be said about the climate is that Earth at this time was not frozen over," Nutman said, explaining that storm wave motion affected the rocks, and "for storm waves to occur, the water could not have been covered by ice."

While the earliest known life on Earth is now believed to have come from Greenland, the researchers don't think there is any particular significance to that location. Nutman said that "we are just looking at a fortunate survivor of the early life record."

Allgood, however, told Discovery News that this kind of general setting -- sedimentary rocks deposited in a body of water -- is what should be targeted in the search for past life on Mars.

"More than any other planet in the solar system, it's clear that Mars was quite similar to Earth in its early history," she explained. "3.7 billion years ago there were bodies of water at the surface, offering a similar kind of environment to the ones that hosted earliest life on Earth and preserved the evidence."

She believes that if more research confirms that the Isua structures are indeed microbial, then there is a good chance that the answer to that question about Mars is "yes."