When you think of planet Earth, you visualize it in oxygen. After all, that’s all we know so far. However, our planet has not always been very hospitable, and oxygen has appeared only in part 2.4 billion Since years.

A recent study by researchers at the University of Connecticut (UConn) showed that before the days of oxygen, microbes on Earth likely survived thanks to the arsenic. You know, substances that can cause cancer and are toxic in the long term, in World Health Organization (World Health Organization).

The study has been published in the journal Communications of Nature, Earth and the EnvironmentTuesday.

See also: The moon has been found to rust despite a lack of oxygen and water

The oxygen cycle that plants and some microbes use in our age takes water, sunlight and carbon dioxide, and then turns them into carbohydrates and oxygen. It is consumed by other organisms that require oxygen to breathe, and the cycle continues.

But as the study showed, half the life of our planet Earth was devoid of oxygen. So how did these other living things survive?

Study lead author and Professor of Marine Sciences and Geosciences at the University of California, Peter FisherAnd his team is just beginning to answer that question.

There were many theories already out there about how life continued on Earth in the days before oxygen became available, but Fisher was not convinced.

Arsenic has been on the list of potentials since 2008 after the evidence was found. And in 2014, Fisher and colleagues discovered further evidence for arsenic-based photosynthesis.

Then, the team found an active microbial mat in Laguna La Brava, in the Atacama Desert in northern Chile, which provided a mutation. These mats live in a completely oxygen-free environment, at high altitudes, where they are exposed to harsh conditions and lots of UV rays. Perfect for comparison with conditions on early Earth days.

Fisher explained This “Water is also high in arsenic. The water that flows over the mats contains hydrogen sulfide, which is volcanic in origin and flows very quickly over these mats. “

“I’ve been working with microbial mats for about 35 years or so. This is the only system on Earth where I can find a microbial mat that works completely in the absence of oxygen. “

What the team discovered was that the mats were creating carbon deposits and producing a new generation of them StromatolitesLayered sedimentary deposits – in many ways thanks to the arsenic.

The use of this type of equipment is not restricted to the ground for conducting such research. Fisher noted The persevering Mars rover would use a similar tool on the red planet to search for life on Mars.