A recent research published in Nature provides new information about the Great Oxidation Event which the Earth faced during its youth. The results from the University of Utah, United States, contradict the general idea about the moment when the planet was filled with oxygen and the foundations for complex life were laid. This would not have been a boom spontaneous and unique, but a gradual process of millions of years.
Today, the vast majority of living beings are adapted to develop by taking advantage of the abundance of oxygen on the planet. Bacteria, plants, fungi, insects, fish and mammals absorb this element to obtain energy. However, 2.5 billion years ago, the scenario was very different; The Earth was covered by carbon dioxide, methane, ammonia and water vapor. These gases predominated due to abundant volcanic and seismic activity. Oxygen was just a small proportion in a sea of components that today we consider toxic.
Until then, microorganisms existed based on chemical processes such as fermentation. For example, archaea historically took advantage of abundant hydrogen for energy through their own enzymes. However, when simpler beings, such as cyanobacteria, developed the mechanism of photosynthesis, the Earth experienced a turning point.
How and when did the Earth become filled with oxygen? This microfossil sheds new light
The microfossil of the organism Navifusa majensis It is the most recent link between photosynthesis and early simple life.
In photosynthesis, carbon dioxide is converted into glucose. The byproduct of this energy conversion is oxygen, which is released into the environment. When countless microorganisms realized that photosynthesis was a more efficient way to live, the Earth filled with the gas we all breathe today. Researchers refer to that moment as the Great Oxidation Event.
Understanding the Great Oxidation Event is harder than it seems
The Great Oxidation Event did not occur on land, but in the seas. Studying oxygen fluctuations in the ocean means investigating environments that have been in constant flux for 2.5 billion years. Although it is a complex task, it is not impossible. Chadlin Ostrander, a geochemist at the University of Utah, used marine shales (a class of rocks) from the South African stratigraphic unit known as the ‘Transvaal Supergroup’.
Ostrander’s team looked for stable isotopes of thallium and other elements to measure changes in oxygen in the sea. Contrary to expectations, they did not find samples that reflected an abrupt transition. Instead, evidence suggests gradual oxygenation that spanned 200 million years.
“The resulting data suggest that the initial rise of O2 in Earth’s atmosphere was dynamic and developed intermittently, until approximately 2.2 billion years ago. “Our data validate this hypothesis and also extend the same dynamics to the ocean,” says Ostrander.
The maturity of the Earth and oxygenation
Another outstanding result of the research is that it seems that oxygenation was not a single event. There were similar attempts before the final Great Oxidation Event, but the planet was not “maturity” enough to host the gas. Previous O2 was only destroyed by reactions between volcanic gases.
“The Earth was not prepared to be oxygenated when oxygen began to be produced. The planet needed time to evolve biologically, geologically and chemically before being conducive to oxygenation. It is like a swing. There is oxygen production, but at the same time there is so much oxygen destruction that nothing happens. We are still trying to determine when the balance tipped completely and the Earth could no longer return to an anoxic atmosphere,” the author explained.
Science has an alternative name for this stage in which the gas flooded everything: oxygen catastrophe. The foundation of the conditions that currently allow complex life led to the extinction of any dominant microorganism whose food source was none other than O2.
The new abundance of oxygen put an end to the hostile greenhouse effect. In addition, it gave rise to the ozone layer, the structure that now protects living beings from the Sun’s ultraviolet rays. After establishing the appropriate conditions, the geological era of fish arrived on Earth, then that of the first amphibians, dinosaurs and finally mammals.
