Where did oxygen come to earth from?
Our planet formed about 4.54 billion years ago, just after the formation of the solar system (geologically speaking). The first dilute atmosphere consisted of hydrogen and helium, light gases captured from interplanetary space. Under the influence of the earth’s heat and the solar wind, it quickly escaped into space, and helium became a relatively rare element.
The second atmosphere lasted much longer and played a decisive role in the geological history of the planet. It consisted mainly of carbon dioxide, methane, water vapor, nitrogen and a number of other gases. Carbon dioxide and methane create a greenhouse effect, so the oceans did not freeze, even though the Sun was much dimmer. This is how the initial conditions for the origin of life were formed in the process of chemical evolution. Interestingly, Saturn’s moon Titan also has a dense nitrogen-methane atmosphere and is therefore considered one of the most promising places in the solar system to search for extraterrestrial life. It’s too cold for liquid water to exist, but it’s still there. oceans and it’s raining from ethane and methane.
About 4 billion years ago, the first living microscopic organisms appeared on Earth. 3.5 billion years ago, some developed the ability to photosynthesize, while others released oxygen into the environment as a byproduct. This process took place on a small scale, and not much oxygen entered the atmosphere for a very long time. It was immediately spent on the oxidation of chemically active substances in water, especially iron.
oxygen disaster
All that changed about 2.4 billion years ago, when cyanobacteria switched to more efficient photosynthesis, using water as the electron source for the reaction. Even cyanobacteria took half a billion years to oxidize anything they could with their byproducts in the ocean. Therefore, the increase in the oxygen concentration in the air started about 2 billion years ago and stopped at 10% of what it is today.
But reactive oxygen is believed to have destroyed much of anaerobic life, including archaeal colonies that use anoxic photosynthesis. According to this estimatedthe biosphere was reduced by 80%; however, due to a lack of data, this event is not equated with well-studied mass extinctions. In addition, when oxygen enters the atmosphere, it oxidizes methane, a highly effective greenhouse gas. As a result, the Huron glaciation began and the earth almost froze. At some points the glaciers practically reach the equator, at least locally.
The second jump in oxygen concentration began 800 million years ago. Scientists do not know the exact reasons for this, but it is clearly related to changes in the biosphere and has progressed in sync with the diversification and complexity of multicellular organisms. According to one version, life stopped interfering with sulfide compounds, which limited oxygen metabolism. All these factors led to the Cambrian Explosion, a period in which biomass grew rapidly and modern animal species (chordates, arthropods, and mollusks) emerged.
Since then, the oxygen level has fluctuated constantly, surpassing a peak of 35% during the Carboniferous period (359-299 million years ago) to reach the current 21%.
Does oxygen equal life?
Without oxygen, complex multicellular organisms would not have arisen on Earth. High concentrations of this gas during the Carboniferous period allowed them to saturate the body and allow large insects such as giant dragonflies to exist. The oxygen-rich atmosphere facilitated breathing and contributed to the intense work of the large muscles. Oxygen is associated with life, and life is associated with oxygen, and if astronomers one day discover a terrestrial exoplanet with a high concentration of oxygen in the atmosphere, they will consider this credible evidence of the existence of the biosphere. But a greater saturation of the atmosphere with oxygen is unlikely to contribute to life.
“There are two main problems. If the oxygen concentration is 60% less than the modern one, it becomes difficult to sustain complex aerobic life; large organisms begin to die. But if the concentration is 60% higher, everything starts to burn. Carboniferous deposits bear the marks of many forest fires, so this is why oxygen is Returning to this level will not bring anything good for our biosphere. Excess oxygen in the air will harm humanity,” Alexander Rodin, general director of the scientific and technical center for monitoring the environment and ecology of the Moscow Institute of Physics and Technology, told socialbites.ca.
The scientist also states that the oxygen content in the air cannot change significantly. Its level in each age is explained by the balance between production and consumption. Oxygen is produced almost exclusively by the biosphere, that is, by land plants and marine organisms.
Oxygen is also consumed above all by life, but not only that. Oxygen oxidizes chemically active substances, is consumed in fires, and turns into ozone under the influence of solar radiation. A large-scale change in the biosphere or a change in climate can shift the balance between production and consumption. But even in this case the changes will not be critical.
Almost everything known about the history of the atmosphere in past geological epochs is questioned because of so little data. But scientists clearly see that the oxygen concentration on Earth today is falling slowly but due to the reduction of green mass. Most likely, this is due to human economic activity.
“I don’t think you can seriously discuss the risk that the oxygen concentration in the air will increase or decrease significantly. If we reduce the mass of green photosynthetic plants this much, all other living organisms in the food chain that still depend on photosynthesis will perish in a fraction of the time before the oxygen disappears. Just starving,” Rodin said.
An equally incredible increase in oxygen levels would not benefit humans and the biosphere. The scientist said that fire hazards aside, modern animals, including humans, could not survive in the Carboniferous atmosphere suitable for giant dragonflies. Oxygen concentration above 23.5% is considered dangerous by modern standards.
Therefore, humanity is lucky that the concentration of oxygen in the air does not increase or decrease too much.