Greenland may be home to Earth’s oldest fossils

3.7-billion-year old mounds signal early microbes


EARLY START  The wavelike mounds of sediment called stromatolites (marked by dashed lines) embedded inside this cross section of a 3.7-billion-year-old rock may be the oldest known fossilized evidence of life on Earth.

A. Nutman, A.C. Allwood/Nature 2016

A melting snow patch in Greenland has revealed what could be the oldest fossilized evidence of life on Earth. The 3.7-billion-year-old structures may help scientists retrace the rise of the first organisms relatively soon after Earth’s formation around 4.5 billion years ago (SN: 2/8/14, p. 16), the discoverers report online August 31 in Nature.

Unlike dinosaur bones, the new fossils are not preserved bits of an ancient critter. The Greenland fossils are mounds of minerals a few centimeters tall that may have been deposited by clusters of microbes several hundred million years after Earth formed. The shape and chemical composition of the mounds, called stromatolites, match those formed by modern bacterial communities living in shallow seawater, says a team led by geologist Allen Nutman of the University of Wollongong in Australia.

If confirmed, the fossils demonstrate that sophisticated, mound-building microbial life appeared early on in Earth’s history. That early start backs up previous genetic and chemical studies that place the advent of basic life on Earth before 4 billion years ago (SN Online: 10/19/15).

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