These may be the oldest fossils on Earth | Science News for Students

These may be the oldest fossils on Earth

Early germs may have left behind these mini mounds 3.7-billion-years ago
Sep 11, 2016 — 7:00 am EST
earliest fossils

These wavelike mounds of 3.7-billion-year-old sediment are called stromatolites (marked by dashed lines). This rock may house the oldest known fossilized evidence of life on Earth.

A. NUTMAN, A.C. ALLWOOD/NATURE 2016

A melting snow patch in Greenland recently revealed tiny mound-like structures. They don’t look like much. But they could just be the oldest signs of life on Earth. And they are a mind-boggling 3.7 billion years old. By studying them, scientists might learn about the rise of the first microbes shortly after Earth formed some 4.5 billion years ago.

Allen Nutman is a geologist at the University of Wollongong in Australia.  His team has just reported on its discovery of those mini-mounds in the August 31 issue of Nature.

Unlike dinosaur bones, the new fossils are not preserved bits of an ancient critter. They are mounds of minerals. Called stromatolites (Stroh-MAT-oh-lytes), each is but a few centimeters tall. Scientists suspect clusters of microbes deposited the minerals. And it would have happened very long ago — perhaps a mere 800 hundred million years after Earth first formed.

Their shape and chemical recipe match those of mounds made by some modern bacteria. These current microbe mineral mounds appear in shallow seas, Nutman’s team notes.

But Abigail Allwood warns that it’s in no way certain that ancient microbes made the old mini mounds. An astrobiologist, Allwood works at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. Something other than living organisms might have caused the minerals to clump onto the seafloor, she points out. Indeed, she argues, the new data are “a little bit thin for what you would usually want to see for such an extraordinary claim.”

Yet if they are super-ancient, the mounds would demonstrate that complex microbes arose early in Earth’s history. And that would support other genetic and chemical studies. Some of them had suggested basic life got its start more than 4 billion years ago. Indeed, Allwood says, if Earthly life emerged that early, then Mars might once have hosted life, too. Early conditions on both planets, she explains, were likely similar in terms of being able to support life.

Power Words

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chemical     A substance formed from two or more atoms that unite (become bonded together) in a fixed proportion and structure. For example, water is a chemical made of two hydrogen atoms bonded to one oxygen atom. Its chemical symbol is H2O. Chemical can also be an adjective that describes properties of materials that are the result of various reactions between different compounds.

fossil     Any preserved remains or traces of ancient life. There are many different types of fossils: The bones and other body parts of dinosaurs are called “body fossils.” Things like footprints are called “trace fossils.” Even specimens of dinosaur poop are fossils. The process of forming fossils is called fossilization.

genetic     Having to do with chromosomes, DNA and the genes contained within DNA. The field of science dealing with these biological instructions is known as genetics. People who work in this field are geneticists.

Greenland     The world’s largest island, Greenland sits between the Arctic Ocean and North Atlantic. Although it is technically apart of North America, just east of Northern Canada, Greenland has been politically more linked to Europe. Indeed, Vikings arrived in Greenland around the 10 th century, and for a time the island was a colony of Denmark. In June 2009, Greenland became an independent nation. Ice covers roughly 80 percent of Greenland. Indeed, the Greenland ice sheet is the world’s largest. If its frozen water were to melt, it could raise sea levels around the world by 6 meters (about 20 feet). Although this is the 12 th biggest nation (based on surface area), it averages the fewest people per square kilometer of its surface area.

Mars     The fourth planet from the sun, just one planet out from Earth. Like Earth, it has seasons and moisture. But its diameter is only about half as big as Earth’s.

microbe     Short for microorganism . A living thing that is too small to see with the unaided eye, including bacteria, some fungi and many other organisms such as amoebas. Most consist of a single cell.

mineral     The crystal-forming substances, such as quartz, apatite, or various carbonates, that make up rock. Most rocks contain several different minerals mish-mashed together. A mineral usually is solid and stable at room temperatures and has a specific formula, or recipe (with atoms occurring in certain proportions) and a specific crystalline structure (meaning that its atoms are organized in certain regular three-dimensional patterns). (in physiology) The same chemicals that are needed by the body to make and feed tissues to maintain health.

NASA     Short for the National Aeronautics and Space Administration. Created in 1958, this U.S. agency has become a leader in space research and in stimulating public interest in space exploration. It was through NASA that the United States sent people into orbit and ultimately to the moon. It has also sent research craft to study planets and other celestial objects in our solar system.

organism     Any living thing, from elephants and plants to bacteria and other types of single-celled life.

planet     A celestial object that orbits a star, is big enough for gravity to have squashed it into a roundish ball and it must have cleared other objects out of the way in its orbital neighborhood. To accomplish the third feat, it must be big enough to pull neighboring objects into the planet itself or to sling-shot them around the planet and off into outer space. Astronomers of the International Astronomical Union (IAU) created this three-part scientific definition of a planet in August 2006 to determine Pluto’s status. Based on that definition, IAU ruled that Pluto did not qualify. The solar system now includes eight planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.

sea     An ocean (or region that is part of an ocean). Unlike lakes and streams, seawater — or ocean water — is salty.

stromatolite     A type of layered rock that forms when cyanobacteria in water create huge communities. Their sticky surfaces trap sediments floating in the water. That accumulating sediment reacts to calcium carbonate in the water. This creates limestone, which builds up very, very slowly. A century-old stromatolite may grow a mere 5 centimeters (2 inches) in size.

NGSS: 

  • MS-LS4-1
  • HS-LS4-1

Citation

Journal: A.P. Nutman et al. Rapid emergence of life shown by discovery of 3,700-million-year-old microbial structuresNature. Published online August 31, 2016. doi: 10.1038/nature19355.

Further Reading

D. Fox. “Invisible fossils of the first animals.” Science News for Students. February 4, 2009.

S. Ornes. “Meteorites may have sparked life on Earth.” Science News for Students.December 17, 2008.