Translated material
Cloudless past
What prevented the Earth from turning into an ice ball billions of years ago?
Scientists have managed to solve one of the mysteries of our geological past: why didn’t the Earth become a huge block of ice 4 billion years ago, when the radiation from the Sun was much weaker than today? Previously it was believed that the problem was the high content of carbon dioxide in the atmosphere and the resulting greenhouse effect. However, Minik Rosing, a professor at the Natural History Museum of Denmark, and Christian Bjerrum, a professor of geology at the Faculty of Geography and Geology at the University of Copenhagen, together with American scientists from Stanford University, found that carbon dioxide levels were not so critical, and clouds were the cause of the warm climate.In 1972, astronomers Carl Sagan and George Mullen formulated the “paradox of a faint early sun.” This paradox was that the Earth's climate during the 4-4.5 billion years of its existence was relatively constant, despite the fact that the radiation of the Sun at that time was 25-30% less than now.
So why wasn’t the Earth covered with a thick layer of ice at an early stage of its history, with such a “weak” Sun?
The most logical answer to this question was proposed in 1993 by the American specialist in the Earth's atmosphere, Jim Kasting. Using theoretical calculations and calculations, he came to the conclusion that 4 billion years ago the Earth's atmosphere consisted of almost a third of carbon dioxide. Consequently, Casting concluded, the huge amount of greenhouse gases protected the planet, like a film, from heat loss and prevented its oceans from freezing and turning into an ice skating rink. For a long time this hypothesis remained the main one.
But scientists Minik Rosing and Christian Bjerrum and their American colleagues decided to refute the established point of view.
Minik Rosing and his colleagues analyzed samples of the oldest rocks on the planet from the town of Isua, located in western Greenland, whose age exceeds 3.8 billion years. The analyzes also made it possible to finally understand the question of whether the carbon dioxide content in the Earth's atmosphere really fluctuated greatly or remained relatively stable? Analysis of rocks from Isua shows that the atmosphere at that time contained no more than one particle of this greenhouse gas per 1000 particles of air. That's three to four times today's carbon dioxide levels, but nowhere near the 30% that Kasting calculated. Consequently, we can conclude that the content of carbon dioxide in the Earth’s atmosphere did not change that much and there is no talk of a greenhouse effect. This means, scientists decided, there were other reasons that influenced the climate of the ancient Earth.
“It was not the high content of carbon dioxide in the Earth’s atmosphere that prevented the ice age from occurring,” says Professor Rosing, “but the fact that the cloud layer in those early years was much thinner than it is now. In addition, the surface of the planet was completely covered with water.”
Few clouds transmitted the rays of the Sun and allowed them to unimpededly heat the ocean, which, like a giant heat accumulator, did not allow the temperature to drop beyond sub-zero levels. The reason for the small number of clouds in the early stages of the Earth’s existence should be sought in the very process of their formation. The fact is that powerful clouds form, as a rule, around condensation centers. It could be simple dust, but it could also be certain chemical compounds, such as iodine. Large quantities of the chemical compounds necessary for the formation of clouds are supplied by plants and bacteria, which did not yet exist at that time.