Before there was oxygen, the first life forms on Earth inhaled this deadly poison

One of the most interesting natural organizations studied by scientists is the microbial mat, the cyanobacteria colony (or “blue algae”). These captivating closed ecosystems are visible to the naked eye and can be found everywhere: in lakes and streams, in soil, and even in artificial environments such as gutter and fountains. drink water.

Given enough time – say 2 to 3 thousand years – the microbial beds will fossilize layer by layer into our oldest fossil-fossil stromatolite layers. And they’ve been doing this for about 3.7 billion years.

Scientists believe that the photosynthetic parts of this ancient microorganism were responsible for producing the oxygen we breathe today. Before they appeared, the planet’s atmosphere was only about 1% oxygen. So what did they breathe during the first 1.5 billion years, and how did they go about photosynthesis without oxygen?

In a new study published in the journal Communications Earth & Environment, researchers led by Pieter T. Visscher from the University of Connecticut (USA) have come up with a convincing answer to this question.

It is that the microorganisms initially photosynthesize from arsenic and release oxygen.

Photosynthesis mainly requires sunlight, water and CO2. In this process CO2 is broken down to carbon and oxygen – plants use part of this oxygen and release the rest. However, without the oxygen molecule, how would all transfers have happened?

Today, there are known microorganisms to live in an oxygen-free environment, but they are not thought to resemble the ancestors to explain ancient photosynthesis in an oxygen-free environment.

There have been several proposed oxygen generation options. For example, photosynthesis may work with iron molecules, but the fossilized evidence does not support that idea. Hydrogen and sulfur have also been proposed, although evidence for them is lacking. Attention began to turn to arsenic (or arsenic), after arsenic-breathing microorganisms were discovered in two super-alkaline lakes in California, Searles Lake and Mono Lake.

In 2014, Visscher and colleagues uncovered signs of arsenic-based photosynthesis, from the “arsenotrophic” microbial carpet deep in fossil samples in Western Australia.

However, given the ever-changing geology of the planets, the fractured ancient fossil record makes it difficult to determine the photosynthesis process of ancient “arsenotrophic”. The fossil record could not determine the role of arsenic it revealed, whether arsenic was involved in photosynthesis or was it just a toxic chemical that happened to be there.

But last year, arsenic-breathing microorganisms were discovered in the Pacific Ocean. And a sulfur bacteria, Ectothiorhodospira sp., also recently discovered capable of converting arsenic from arsenite compounds at Big Soda Lake in Nevada, USA.

Before there was oxygen the first life forms on Earth inhaled this deadly poison | Explore

Area discovered microorganism carpet in Northern Chile.

The content of the study report said that Visscher discovered a living microbial mat thriving in an arsenic-filled environment in Laguna La Brava in the Atacama desert in Chile.

“We started working in Chile”, Visscher shared, “Where I found a blood-red river. The red sediments are made up of photosynthetic anoxogenic bacteria. The water is also very high in arsenic. Water flows through microorganisms that contain hydrogen sulfide. It’s volcanic in origin and it flows very quickly on these rugs. Absolutely no oxygen. “

These microorganisms have not been studied before and their conditions are similar to those of early Earth. It is a state of permanent absence of oxygen at high altitudes with extreme temperature changes and exposure to ultraviolet rays.

The above microorganisms are somewhat similar to Ectothiorhodospira sp. in Nevada, when carbonate deposits are created, new stalactites form. Most interestingly, those deposits contain evidence that they are metabolizing arsenic. The fast-flowing waters around the carpet are also rich in hydrogen sulphide and arsenic.

“I have been working with micro-mat for about 35 years or so. This is the only system on Earth where I can find micro-mat that works completely in hypoxia,” Visscher said.

And the important thing is that it is not Earth where this is possible. Visscher notes that the equipment they use to study the aforementioned micro-mats is no different from the system on Nasa’s Mars probe.

“When they look for evidence of life on Mars, they often consider the existence of iron. And maybe they should also look at arsenic,” the researcher added.

Refer BigThink

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