Unique rock formations from Puna de Atacama in Argentina could provide a window into early life on Earth

Stromatolite fossils from Puna de Atacama in Argentina are providing scientists with invaluable material for studying early life on Earth.

stromatolite
An image of fossilised stromatolites from 650 million years ago during the Vendian period (Precambrian), Bolivia. Credit: Xenomanes

Stromatolites—also known as stromatoliths—are sedimentary formations made by photosynthetic microorganisms, organisms that turn light energy from the sun into chemical energy used in cellular processes. A team of researchers researching modern stromatolites in Argentina’s Puna de Atacama region believes they can offer a tantalising glimpse into the origins of the earliest life forms on Earth.

Stromatolite formation

During photosynthesis, cyanobacteria and other microorganisms such as sulfate-reducing bacteria process light, gaseous compounds, and organic matter alongside each other. The culmination of biochemical processes results in the generation of sulfur and oxygen.

These elements build up and further result in oscillating gradients. These gradients cause different functional groups of microorganisms to stratify into layers or “microbial mats”.

Like modern stromatolites, stromatolites from 3450 million years ago (during the Precambrian era when life on Earth was thought to have begun) also display a laminated structure.

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Some of the earliest microscopic fossils

Astrobiologist Dr. Brian Hynek worked alongside fellow researchers at the Puna de Atacama site, examining some of the earliest microscopic fossils in the large mounds of rocks there.

Dr. Hynek and his colleagues believe that the bacteria still living in places like the Puna de Atacama site are utilising the same biological processes and reactions as those from billions of years in the past. By studying the modern stromatolites, like those at Puna de Atacama, scientists could learn more about the genesis and workings of early life on Earth.

In their recent AGU publication the abstract mentions: "Stromatolite structures in the rock record from at least 3.5 billion years ago represent the earliest fossil evidence for life on Earth; thus modern examples have received great attention."

There are not many places left with stromatolites resembling those from ancient Earth. Dr. Hynek proposes the idea that stromatolites may have developed on Mars and encourages rover exploration.

Dr. Hynek told CU Boulder Today "Understanding these modern communities on Earth could inform us about what we should look for as we search for similar features in the Martian rocks.”

He notes the presence of similar salts in dried-up lakes on Mars, matching those identified in the team's Argentina study. Although the team had limited time during their first visit, they plan to return to collect more samples and understand the conditions supporting microbial growth.