3.5 billion-year-old rock structures are one of the oldest signs of life on Earth
Layered rocks in Western Australia are some of the earliest known life on Earth, according to a new study.
The fossils in question are stromatolites, layered rocks formed by the secretions of photosynthetic microbes. The oldest stromatolites that scientists agree were made by living organisms date back to 3.43 billion years, but there are older specimens as well. Stromatolites dating back 3.48 billion years have been found in the Dresser Formation of Western Australia.
However, billions of years have wiped out traces of organic matter in these older stromatolites, raising the question of whether they were really formed by microbes or whether they were created by other geological processes.
The new study’s verdict: It was old life.
“We were able to find certain specific microstructures in certain layers of these rocks that strongly indicate biological processes,” he said Keyron Hickman-Lewis (opens in new tab)a paleontologist at the Natural History Museum in London, who led the study.
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Microbial Mats
The findings may have implications for the search for life on Mars, Hickman-Lewis told Live Science. The stromatolites in the Dresser Formation are inlaid with iron oxide due to the reaction of iron with oxygen in the atmosphere. The surface of Mars has been oxidized in the same way — thus the rusty orange color — but the rocks may contain similar structures left behind by ancient life on Mars, Hickman-Lewis said.
Hickman-Lewis and his team examined Western Australian stromatolites first discovered in 2000 by study co-author Frances Westall (opens in new tab) at the National Center for Scientific Research (CNRS) in France. They used a variety of high-resolution 2D and 3D imaging techniques to look into the layers of the stromatolite at a fine scale.
What they saw indicated biological growth in all its messy glory. The researchers observed uneven layers, including small dome shapes indicative of photosynthesissince microbes with the most access to the Sun will grow more vigorously than those not so high in the structure. They also saw columnar structures typical of modern stromatolites, which are still found in a few locations around the world.
“Microbial mats give you layers that are uneven in thickness and tend to be wrinkly or wrinkled or go up and down on very small spatial scales,” said Linda Kaho (opens in new tab), a sedimentologist and geochemist at the University of Tennessee who was not involved in the new study. Putting all the structural clues together, she told Live Science, “you end up getting what looks like the characteristics of a microbial mat.”
Martian microbes?
Evidence that the Dresser Formation stromatolites are signs of ancient life does not make them the oldest life on earth. That (possible) honor may go to stromatolites found in 3.7 billion year old rock in Greenlandor possibly to microfossils from Canada that may be 4.29 billion years old. However, it is very difficult to distinguish biological life from inorganic processes in these very old rocks, so these finds and others from a similar time frame are controversial.
Based on the minerals in the stromatolites, Western Australia’s microbial mats likely formed in a shallow lagoon fed by hydrothermal vents also connected to the ocean, the researchers reported Nov. 4 in the journal. Geology (opens in new tab).
The techniques used to study Western Australian stromatolites could be useful for searching for life on Mars, Hickman-Lewis said, especially if Mars samples can be returned to Soil.
Scientists should “think of some of the analyzes here as a trial run of the analyzes we’ll have to do in about a decade when we have material from Mars.”
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