The oldest fossils in the world discovered

Microbial stromatolites on Greenland are 3.7 billion years old

Stromatolites like here in Yalgroup National Park on the Australian coast could have existed 3.7 billion years ago © C. Eeckhout / CC-by-sa 3.0
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The earthly life is older than thought: Researchers have discovered in Greenland perhaps the oldest fossils on earth. These are 3.7 billion year old stromatolites - stratified deposits most likely produced by microbes. If this were confirmed, these would be the earliest known traces of life at all, as the researchers report in the journal "Nature".

When, how and where the first life was formed on our planet is unknown. Because the first organisms were unicellular and therefore not preserved, their existence can only be indirectly proven - through the traces they leave behind in their environment. These include stromatolites - finely layered sediment pads that are still formed by bacterial mats.

Fund in Greenland's Greenstone Belt

Stromatolites in the approximately 3.5 billion year old sedimentary formations Strelley Pool and Pilbara in western Australia have so far been regarded as the oldest relicts of prehistoric life.

Now, however, Allen Nutman of the University of Wollongong, Australia, and his colleagues have discovered possible remnants of stromatolites in Greenland's 3.8 billion year old Isuas greenstone belt. So far, this formation has not been very promising for fossil finds because the rock has been severely deformed and altered over the course of millions of years by heat and pressure.

Telltale layers

But by a lucky coincidence, the researchers discovered an approximately 30 by 70 meters large area of ​​the Isua greenstone, which had largely escaped this metamorphosis. This 3.7- to 3.8-billion-year-old formation had only been exposed to the thawing snow and ice due to the warmer climate. display

Allen Nutman and a colleague with a sample of 3.7 billion year old stromatolites from Greenland. Yuri Amelin

At two points in the rock, the scientists came across millimeter-thin layered structures of one to four centimeters in height, some of which protruded conically and sometimes resembled rather flat cushions. From the shape and layering of the structures, Nutman and his colleagues conclude that these must be fossils of primeval stromatolites and thus possibly the oldest traces of earthly life.

Analyzes speak for biogenic origin

But whether a fumed stromatolite was actually produced by primeval microbes or only by non-biological processes, is not easy to determine. The researchers therefore carried out supplementary chemical and geophysical analyzes. Both the accumulation of titanium and potassium as well as the distribution of carbon and oxygen isotopes argue that they are stromatolites created by microbes.

The steep, asymmetrical shape of the stream elites and the type of stratification are also indicative of a biogenic origin. Both are similar to the primeval stromatolites that had previously been found in Australia. "For all these reasons, we exclude an abiotic origin of the Isua stromatolites, " the scientists emphasize.

Already 3.7 billion years ago

"It provides evidence of primeval life in a 3.7-billion-year-old metacarbonate formation of the Isua Greenstone, " note Nutman and his colleagues. Should this be confirmed, then the emergence of life on our planet will shift a little further forward. Simple microbes were therefore found in the primal ocean right after the phase of large meteorite impacts.

This, in turn, has implications for our search for life on other planets: "All of a sudden, Mars appears as a much more promising candidate for primeval life, " writes Abigail Allwood of NASA's Jet Propulsion Laboratory Comment. Because at the time when the microbes in Greenland were building their stromatolites, our neighbor planet was still life-friendly. (Nature, 2016; doi: 10.1038 / nature19355)

(Nature, 01.09.2016 - NPO)