Ecosystem may have clues about the origin of life on Earth – 12/21/2023 – Science

A reflection of the first forms of life on our planet.

That’s what a team of scientists claims to have found in a “unique in the world” lagoon ecosystem in the Atacama Puna, Argentina.

The discovery, made by geologist Brian Hynek, from the University of Colorado in Boulder, and Argentine microbiologist María Farías, was announced last week and occurred after studying satellite images of the region.

Hynek and Farías analyzed these images for more than a year and found what appeared to be a particular network of aquifers in the middle of the desert.

They decided to visit this inhospitable plateau at almost 4,500 meters above sea level and there they found a dozen lagoons with clear, extremely salty water, whose bottoms were covered by green mounds of stromatolites.

Stromatolites, also known as living rocks, are microbial reefs formed by mineral grains glued together by a group of bacteria.

According to NASA, they represent the oldest fossil evidence of life on our planet, and date back to at least 3.5 billion years ago.

Since their origin, they obtained energy from the Sun and, by producing oxygen, they increased the volume of this chemical element in the planet’s atmosphere to around 20%, allowing life to thrive on Earth.

It is estimated that planet Earth was formed 4.5 billion years ago.

At that time and for many years, our planet was very different from what it is today.

The first fossil records on the planet

When the stromatolites emerged, the continents were still forming, so there was a lot of volcanic activity.

The waters were laden with arsenic and were much more saline than the seas we have today.

María Eugenia Farías, co-author of the discovery, explained in an interview with BBC Mundo (BBC service in Spanish) that there was also no oxygen or ozone layer.

“Under these conditions, the first forms of life emerge, which are protobacteria: bacteria that associate and form colonies”, says the Argentine scientist.

During this colony formation process, bacteria capture carbon dioxide.

“Part of this carbon dioxide turns into organic matter and another turns into calcium bicarbonate, which forms a kind of living rock and is what we know as stromatolites,” says Farías.

“These are the first fossil records on the planet.”

An environment similar to that of 3.5 billion years ago

Stromatolites released oxygen first into the oceans, then into the atmosphere, and later created the ozone layer.

María Eugenia Farías explains that during the Cambrian period, already on a planet with oxygen, the life of eukaryotes exploded: “Plants and animals appeared that ate and displaced the stromatolites.”

The conditions on this primitive planet from 3.5 billion years ago are those that occur in environments where stromatolites are still found, typically places with low oxygen levels, high ultraviolet radiation, volcanic activity and saline waters.

Stromatolites still live in some salt lakes or bays around the world. These are places where there are not many predators that can eat them.

Australia is notable for its variety of stromatolite habitats, both living and fossilized.

Shark Bay, also known as Shark Bay, in Western Australia contains one of its largest habitats.

But, according to Farías, the ecosystem found in the Andes is different due to its location more than 3,600 meters above sea level.

“The conditions in the Atacama Puna, in Argentina, Chile and Bolivia, are special. It is surrounded by volcanoes, has low oxygen pressure and high ultraviolet radiation due to the altitude and has saline lagoons loaded with arsenic”, he continues.

“These are conditions very similar to those that existed on Earth during the first forms of life.”

A piece of Mars on Earth

Hynek and Farías plan to return to the Atacama Puna soon to continue investigating gypsum stromatolites specifically.

“Stromatolites are generally made of calcium carbonate, but gypsum ones are formed under thalasic conditions, that is, with a very high concentration of salt, conditions also very similar to those on Mars,” says Farías.

The scientist highlights that on that planet there is a crater where there is a large concentration of water so saline that it does not freeze.

“As we have not yet been able to reach Mars to find out if life exists, at least we can see a counterpart to this environment here on Earth, in the Atacama Puna.”