Click here to eTiny ripples of sediment on ancient seafloor, captured inside a 3.7-billion-year-old rock in Greenland, may be the oldest fossils of living organisms ever found on Earth, according to a new study.
These cone-shaped structures discovered in 3.7-billion-year-old rocks in Greenland, about the size of a quarter, may be fossilized colonies of microbes and the earliest fossils of life on Earth, researchers say.
"[T]here were similar environments in bodies of water standing at the surface of Mars, offering a similar kind of environment to the ones that hosted the early evidence of life on Earth, at Isua and younger," she said.
"The overall features, such as the shape of the stromatolites, are preserved," Nutman said.
Allwood added that there is also clear evidence that, at the time the rocks at Isua were forming 3.7 billion years ago, conditions on Mars were similar to those on early Earth.
The researchers said the ripples are the fossilized remains of cone-shaped stromatolites, layered mounds of sediment and carbonates that build up around colonies of microbes that grow on the floor of shallow seas or lakes.
The rock outcrop was found only after a series of warm summers in southwestern Greenland caused large patches of snow at the site to melt earlier than normal, revealing rocks that had not been examined by researchers since the Isua Greenstone Belt was first explored in the 1980s, Nutman told Live Science.
The research, led by Allen Nutman, head of the School of Earth and Environmental Sciences at the University of Wollongong in Australia, described the discovery of what look like tiny waves, 0.4 to 1.5 inches (1 to 4 centimeters) high, frozen in a cross section of the surface of an outcrop of rock in the Isua Greenstone Belt in southwestern Greenland, a formation made up of what geologists regard as the oldest rocks on the Earth's surface.
Allwood reviewed the new study by Nutman and his colleagues for a separate opinion piece published today (Aug. 31) in the journal Nature.
Until now, there had been a gap between the start of the fossil record on Earth and the youngest areas on Mars, where there was good evidence for standing bodies of water in the past.
[Photos: The World's 6 Most Famous Rocks] "These kinds of discoveries always do [cause controversy], especially when they first come out, and in this case, it's particularly amazing because they were found in metamorphic rocks that have been significantly altered and transformed from their original characteristics," Allwood told Live Science.
The 3.7-billion-year-old structures described in the new study are about 220 million years older than the fossils previously regarded as the oldest known fossils on Earth.
[7 Theories on the Origin of Life] According to the scientists, the new discovery, detailed online today (Aug. 31) in the journal Nature, supports theories that life on Earth originated during the so-called Hadean eon more than 4 billion years ago, a period of intense volcanic activity when large meteorites and icy comets frequently bombarded Earth.
He told Live Science that the new finds would no doubt face further scientific tests to assess the strength of the claims for a biological origin.
This means that the structures are not only evidence of standing bodies of water on the Earth's surface 3.7 billion years ago, but also bodies of land crossed by rivers that carried chemical solutes into the ancient oceans, he said.
"Most of the rocks there are very deformed and modified by later mountain-building processes, but you do find just very tiny little areas that have survived with their original volcanic or sedimentary structures not destroyed," Nutman said.
Those 3.5-billion-year-old stromatolites, found in sedimentary rocks in Western Australia, precipitated over billions of years without metamorphic heating.