The team of geologists discovered an unusual mechanism of "self-control" in microbes and plants, thanks to which our planet has not yet turned into an ice block due to the absorption of CO2 by trees and algae.
According to the representative of the Spanish Autonomous University of Barcelona Sarah Egglestone, when researchers measured the concentration of CO2 in ice deposits, they found that the level of carbon dioxide in the atmosphere has almost always been above 180 parts per million over the past 800 thousand years. This was surprising because it indicates that low carbon dioxide levels are fairly stable. This also made it possible for scientists to assume that the level of CO2 in the entire history of the existence of multicellular life on our planet did not fall below this mark.
Before the first microbes and plants appeared on Earth, its atmosphere was almost entirely composed of methane, carbon dioxide, nitrogen and other greenhouse gases. Oxygen began to appear in the atmosphere about 2.2 billion years ago, after the "great oxygen catastrophe", during which the first microbes capable of photosynthesis began to absorb carbon dioxide and saturate the atmosphere with oxygen.
Thus, the greenhouse effect weakened, and, according to the assumptions of researchers, about 850-600 million years ago, our planet transformed into a kind of snowball, because the temperature indicators dropped so much that the oceans began to freeze up to the equator. There are still heated debates among scientists about how the Earth managed to get out of this glaciation.
As Egglestone and her colleague Eric Galbraith point out, the question of why nothing like this happened in the next six million years is even more heated. During this time period, the level of carbon dioxide in the atmosphere fluctuated from very high levels (typical for the dinosaur period) to very low levels, which is typical for the Carboniferous period and the modern era, and why, despite such changes, the planet remained free of ice.
Egglestone and Galbraith, in search of an answer to these questions, were studying changes in the concentration of carbon dioxide in the earth's atmosphere over the past 800 thousand years. For this, an analysis of the Antarctic ice was carried out, which was formed during the periods of the onset and retreat of ice ages.
Thanks to these data, an interesting trend was established - as it was found out, the level of carbon dioxide never fell below 190 parts per million. Moreover, at this level, the CO2 concentration was practically not affected by changes in the inclination of the planet's axis of rotation, the onset or retreat of ice, the fall or increase in average annual temperature indicators, the activity of volcanoes, as well as many other factors related to space and nature.
The authors of the study believe that the stabilization of carbon dioxide levels and the neutralization of all these factors were facilitated by plants, the efficiency of photosynthesis and the growth rate of which, with a decrease in carbon dioxide concentration, sharply decreases below the limit of 200 ppm. First of all, as laboratory studies have shown, this is typical for the main CO2 consumers on Earth - cyanobacteria.
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Thus, when the level of carbon dioxide falls below the critical level, the plants dramatically decrease their appetite. And this, in turn, leads to the fact that due to the emission of volcanic gases and the massive decomposition of dead plants, the concentration of carbon dioxide begins to grow again.
All this, according to scientists, makes it possible to assert that photosynthetic organisms in this case do not contribute to the onset of global glaciation, as in the period of the "great oxygen catastrophe", but prevent it. Such a relationship between plants and nature, experts say, over the past 600 million years have kept our planet from turning into ice.
