Billions of years ago, living things on Earth were mostly thin microbes that lived in shallow water. In many cases, these microbial communities have formed carbonate minerals that have accumulated over the years. Limestone stones with stones called stromatolites. They are the oldest evidence of life on earth. But organic organisms do not tell researchers how they formed.
Today, most life is supported by oxygen. But these microbial mats have existed for over a billion years Before oxygen is present in the atmosphere. So what did you use instead of life?
Our team Geologist, Physicist And Biologists There were indications in organic stromatolites that arsenic was a chemical of ancient light modification and respiration selection. But modern versions of these microbial community communities still live on Earth today. Perhaps one of these is arsenic used and can provide evidence for our theory?
So we embarked on an expedition of scientists from Chile and Argentina to search for living stromatolites in the extremes of the High Andes. In a small stream deep in Atacama Desert, We got a big surprise. The bottom of the channel was bright purple and was composed of stromatolite-building microbial mats that thrive in the complete absence of oxygen. Just as the information we received from ancient living beings suggested, these rocks use two different forms of arsenic for photosynthesis and respiration. Our research so far provides the strongest evidence of how the oldest life on Earth survived in a pre-oxygen world.Christophe Dupers, Anthony Batton, Peter Wischer, CC BY-ND
Converting sunshine into pleasure
For the past 2.4 billion years, photosynthetic plants and Blue-green cyanobacteria Uses sunlight, water, and carbon dioxide to make oxygen and organic matter. In doing so, they replace the Sun Reza used by life with the Sun. Other bacteria breathe in oxygen because they digest organic carbon and in the process get the energy they need to breathe.
In the ancient world, germs also gained energy from sunlight, but their basic machinery Could not make oxygen from water Or use oxygen to breathe. They needed another chemical to do that.
From a biochemical point of view, there are only a few possible candidates: iron, sulfur, hydrogen or arsenic. Lack of evidence in biological records and reduced amounts of some of these chemicals Etc. in the soup Suggests that neither iron, sulfur nor hydrogen will possibly be candidates for the initial form of light modification. Which leaves arsenic.
In 2014, our team received the first clue that stromatolites were produced by arsenic-assisted light modification and respiration. We collected the pieces 72.7272 billion year old stromatolites From the pre-oxygen world by drilling in ancient reefs Australia’s comeback. We then took the samples to France and cut them into thin slices. By measuring the X-rays from these samples when we bombarded them with photons, We mapped the chemical elements in the sample. If there are two types of arsenic on the map, it is an indication that life was using arsenic for photosynthesis and respiration. In these relics of ancient life we found both forms of arsenic, but not of iron or sulfur.
It was complicated, but we want more evidence: a modern analog to help prove our arsenic theory. No researcher has ever found an oxygen-free microbial matte community anywhere, but if we do find one, it may help us to point out that when there was a lack of oxygen in the oceans and atmosphere of our planet, first stromatolites How to makeDuring D’Azelo, CC BY-ND
Modern microbiology, ancient analogues
Chile’s Atacama Desert is the most open space on Earth, represented by volcanoes and exposed to high levels of UV radiation. It’s not much different from what the Earth looked like 3 billion years ago and wasn’t exactly as supportive of life as we know it to be. Here – with the help of a team that spread across four continents and seven countries – we found what we were looking for.
Or the destination was Laguna La Brava, a very salty lake that is deep in the rugged desert. The volcano was fed by the earth’s water springs and a sudden current flowed towards the lake. Streambed was a unique, dark purple color. The color came from a microscopic mattress that happily thrives in water that contains an unusual amount of arsenic, sulfur and lithium, but one important element is missing – oxygen.
Can these thin purple blobs answer an old question?Peter Wescher, CC BY-ND
We cut out a piece of mattress and searched for evidence of minerals. A drop of acid turned the mineral into fizzy-carbonate! – This microscopic group was forming low stroma stromatolites. So our team went to work, camped on site for a few days at a time.
We measured the water and mattress chemistry with our farm equipment during the day and night, summer and winter. Not once did we get oxygen, and back in the lab we confirmed that sulfur and arsenic were abundant. Looking at the microscope, we saw purple photosynthetic bacteria, but the oxygen-producing cyanobacteria were very much absent. We also collected DNA samples from the mattress and found genes for arsenic metabolism.
In the lab, we mixed germs from the mattress, added arsenic and exposed the mixture to sunlight. Photosynthesis was taking place. Microbes used both arsenic and sulfur, but preferred arsenic. When we added a small amount of organic matter, a different arsenic mixture was used for respiration and was preferred over sulfur.
What was left was to show that two types of arsenic could be detected in modern stromatolites. We went back to France, and made chemical maps from Chilean samples using an X-ray extraction technique. Every experiment we did was supported The presence of a strong arsenic cycle In the absence of oxygen in this unique modern stromatolite. This is beyond doubt, confirming the idea that the organic Australian specimens we studied in 2014 showed evidence of an active arsenic cycle in a long time on our young planet.Peter Wescher, CC BY-ND
North of Earth, leads Mars
The harsh conditions of Atacama are similar to the initial atmosphere of Mars and Earth NASA scientists and astronomers turn to Atacama To answer questions about how life began on our planet, and where it could begin. The arsenic-cycling mats we found at Laguna La Brava offer tough clues to some of the most basic questions about life.
The rover aboard the Mars 2020, which is currently suffering from space, is a device that can be used to see the elements. Exactly the same process we used to map our elements. It may be found that the rocks on Mars are rich in arsenic, which suggests that life on Mars also used arsenic. It has done so on Earth for a billion years. In the most difficult situations, life finds a way, and that is the way We are trying to understand.