Carbon dioxide saved the Earth from global glaciation
Scientists have established why the ancient Earth was not covered with ice. Previous studies have shown that solar-type stars shine very faintly at the beginning of their existence. So, 3.8 billion years ago, the radiation of our star was 75% lower than it is now. This should have led to an ice age on the planet, but it did not happen, arXiv.org reports.
The authors of the study, in an attempt to resolve this paradox, modeled various options for the atmosphere of the young Earth. The results showed that the planet was able to keep warm due to its high carbon dioxide content.
The early Sun was emitting large amounts of ultraviolet light. He affected the upper atmosphere. If the concentration of CO2 were the same as today, then the gas shell of the Earth would quickly evaporate into space. When heated, gas molecules acquire a higher velocity, which helps them to leave the gravitational zone. In addition, the hot gas is expanding and moving away from the center of the planet.
Calculations showed that in order to maintain a stable dense atmosphere, the carbon dioxide content in it had to be at least 40% – much more than previous estimates showed. Scientists emphasized that 40% is the lower limit, in fact, the level could be much higher. Note that now CO2 is 0.4% of the earth's atmosphere.
Carbon dioxide provided a powerful greenhouse effect that kept the planet warm even when the sun was faintly glowing. When its amount naturally decreased, glaciation began. But this happened much later – about 2.2 billion years ago. But by that time, life had already arisen on Earth, and some of its primitive forms were able to survive the ice age.
Scientists have previously modeled the appearance of the early Earth. According to them, it could turn out to be a completely aquatic world.
