Bacteria are persecuted and subject to health campaigns, but few people know that if it were not for a specific form of these tiny beings, life would not have sprouted on our planet. In fact, life on Earth took “little” to appear after the formation of the planet thanks to the action of bacteria.

At least 3.7 billion years ago, and perhaps hundreds of millions of years before, there were already beings able to reproduce in a world where the oceans had just appeared.

There was an element that made it possible for those beings to begin to cooperate with each other and eventually the animals appeared, only five hundred million years ago.

Oxygen was the fuel that spurred the metabolism of living beings and transformed our planet into an inhabited world, but there are still doubts about how it appeared.

Life Sprouts into Existence

The geological study indicates that until about 2.4 billion years ago there was no oxygen in the Earth’s atmosphere or in its oceans.

From that moment, in three explosions, the percentage of this gas increased until it occupied 21% of the atmosphere.

One of the most accepted explanations is responsible for the atmospheric overturn of cyanobacteria, microbes that began using the sun’s energy to produce carbohydrates and oxygen from water and carbon dioxide.

This new technique, which we now know as photosynthesis, gave these organisms unprecedented success. But better is always worse for some.

The beings who had satisfied their energy needs for more than a billion years without oxygen discovered that this new gas was poison to their cells.

That was a change of regime and the triumph of cyanobacteria was such that today all the plants on Earth have incorporated them into their organisms in the form of organelles baptized as chloroplasts.

If atmospheric oxygen increased a small percentage above the current 21%. That would significantly limit the Earth’s biosphere and reduce oxygen production.

Then, it took almost 2,000 million years until oxygen levels were enough to allow the existence of the first animals.

The scientific debate that tries to explain this process has been intense. Now a team from the University of Leeds in the United Kingdom has developed a model according to which, beyond the appearance of the first photosynthetic microbes and the movement of tectonic plates the increase of the essential gas for life in the atmosphere was a matter of time.

Both photosynthesis and plate tectonics, which began around 3,000 million years ago had influence in the oxygenation of the Earth.

Oxygen is not a rare substance. It is the third most abundant element in the universe, after hydrogen and helium. It is tremendously “sociable” and can form compounds with almost all the elements of the periodic table.

For many millions of years, the interior of the Earth maintained the high temperature reached during its formation, but the progressive cooling reduced the number of volcanic gases that arose from its interior.

These gases were what, when reacting with oxygen, removed it from the atmosphere. This change in balance allowed the oxygen produced by the cyanobacteria to start generating a surplus that accumulated over time.

The new model would explain the intriguing interval between the appearance of the organisms that produced oxygen and the increase of this gas in the atmosphere.

Planets with oxygen would be more frequent than previously thought because improbable biological advances are not necessary.

Then these changes in atmospheric balance affected the amount of phosphorus in the sea, which depends on oxygen levels, and that had an impact on animals that lived on photosynthesis, which in turn used phosphorus.

When these feedback processes produced a third increase in the percentage of oxygen in the atmosphere, the Earth was ready for the explosion of complex, mobile and visible life forms that have inhabited the planet since then.

In addition to knowing that these essential processes were necessary for the appearance of life on Earth, scientific models suggest that planets with atmospheres of abundant oxygen may occur more frequently than previously thought because for its appearance there is no need for multiple and very unlikely biological advances or casual tectonic events.

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