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Scientists have discovered a previously hidden ecosystem with an extensive lagoon system in the Puna de Atacama salt flats, an arid plateau in Argentina – with giant stromatolites that could provide insight into the earliest life on earth and possibly even Mars, according to new research.
Stromatilites are layered rocks formed by the growth of blue-green algae, or cyanobacteria, through photosynthesis. The structures are considered one of the oldest ecosystems on earth, according to NASA, showing the earliest fossil evidence of life on our planet from at least 3½ billion years ago.
“These are definitely like some of the earliest macrofossils on our planet, and really in a rare type of environment on today’s Earth,” said Brian Hynek, professor. in the Department of Geological Sciences at the University of Colorado Boulder, who helped document the ecosystem. “They are a glimpse into the distant past of what life looked like on our planet 3½ billion years ago.”
Ancient giant stromatolites were widely used in the Earth’s Precambrian era, which spans the early period from about 4.6 billion to 541 million years ago, but now they are scattered around the world. The most well-developed areas are in the Bahamas and the Shark Bay area of Western Australia, according to non-profit conservation organization Bush Heritage Australia.
Modern stromatolites are relatively small, Hynek said, but ancient stromatolites grew to 20 feet (6 meters) tall and 16 to 22 feet (5 to 7 meters) wide, he said. Beneath the waters of the Puna de Atacama lagoon, the recently uncovered stromatolites are up to 15 feet (4.5 meters) wide and several feet tall, according to a news release from the University of Colorado Boulder.
Stromatolites usually grow in alkaline conditions, but the Puna de Atacama lagoon system is acidic. The stromatolites found today are almost all carbonate rocks (made of limestone), but these structures are mainly composed of the minerals gypsum and halite (rock salt), said Hynek.
It’s not clear why the stromatolites are so large, Hynek said, but he said the inland ecosystem sat undisturbed for a long period of time, allowing them to grow unhindered.
More about ancient stromatolites
Unlike modern stromatolites, ancient stromatolites grew in a period when there was no oxygen in the atmosphere. In these conditions, the microbes of the stromatolites used anoxic photosynthesis, which does not require oxygen, to convert light energy into compounds that support living cells.
“It’s amazing to find structures that could be biogenic (produced by living organisms) at this unusual height,” said Pieter Visscher, a professor of marine sciences at the University of Connecticut who has studied stromatlites extensively. , in an email. “A big issue with the discovery, whether it’s biogenic or not, is that these are created in the presence of oxygen (in the current atmosphere). Until 2.3 billion years ago, there was no oxygen.”
While the stromatolites are in an environment where there is oxygen, Hynek said he believes that the layers further down in the rock have little access to oxygen and are actively created by microbes using anoxic photosynthesis. This would make the structures similar to those found on ancient Earth.
Hynek saw the lagoon system through satellite imagery in April 2022 when he was studying another lagoon in northwestern Argentina that contained smaller stromatolites with microbes that use anoxic photosynthesis.
“We are not sure if the microbes are actively participating in their growth (in the newly discovered stromatolites). We think they are. But we haven’t done the experiments yet to try to figure that part out,” said Hynek, who documented preliminary observations with microbiologist Maria Farías, co-founder of Punabio SA Environmental Consulting. “There is a lot of work to be done. We discovered them and barely scratched the surface.”
Hynek and Farías planned to present their findings on Dec. 11 at the 2023 meeting of the American Geophysical Union in San Francisco, according to a news release.
A possible window into ancient Mars
If microbes produce the stromatolites using anoxic photosynthesis, the discovery could shed light on the possibility of life on ancient Mars, Hynek said.
“We have identified more than 600 ancient lakes on Mars; maybe there was even an ocean there. So, it was a lot more like Earth early on,” he said. Hynek added that the minerals gypsum and halite, found in the stromatolites in Argentina, are also found in salt deposits throughout Mars.
“If Mars ever changed life through photosynthesis, this is the kind of thing we’d be looking for (stromatolites) — and it’s the kind of thing we’re looking for,” said Hynek, who is a research associate at the Center. University of Colorado Boulder Laboratory for Atmospheric and Space Physics.
“If we’re going to find any kind of fossils on Mars, this is our best guess as to what they would be, because these are the oldest from the Earth’s rock record.”
Hynek said he hopes to return to the lagoon soon to do more research on the stromatolites.
“Stromatolites on Mars? Long shot, but who knows. So far, there are no carbonates on the surface of Mars, but the search continues,” said Visscher, for possible signs of life.
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