An examination of fossils in China has helped explain why the Earth was not covered in ice 1.5 billion years ago
20.10.2003
American researchers who gathered information about the nature of the Earth's ancient atmosphere came to the conclusion that the "greenhouse effect" is not just a phenomenon of the modern era. According to the data, it also affected the planet about 1.5 billion years ago.
The study is based on the analysis of fossils discovered in northern China, which proved that at that time there was a large concentration of carbon dioxide in the atmosphere, 10 to 200 times its current level. The researchers claim that this is proof of the existence of the "greenhouse effect" right after free oxygen appeared in our atmosphere, over 2 billion years ago.
The surface temperature of a planet is determined on the basis of the balance between the rate of its heating by solar radiation and internal heat sources (radioactive substances), and the rate of its cooling, due to the emission of energy into space. Without the atmosphere, the current average temperature of the Earth's surface would be about 30 degrees lower - which would have ruled a perpetual ice age here.
Since the earth was formed, and at least about 4 billion years ago, the temperature of its surface allowed water to exist in a liquid state. This, thanks to the combination of temperature and atmospheric pressure, together with the gas mantle, which plays an essential role here. The gases that create the "greenhouse effect", such as carbon dioxide and methane, cause the temperature to rise by "trapping" heat.
Until now, it was not clear what was the amount of carbon dioxide that the earth's atmosphere contained before the appearance of oxygen, more than 2 billion years ago. The researchers isolated single-celled algae fossils found in soil layers dating from 1.4 billion years ago, when the free oxygen emitted into the atmosphere reduced the amount of free methane.
The calcium mantle of the microscopic fossils was tested by measuring the isotope ratio between carbon-13 and carbon-12. It was found that the high concentration of carbon dioxide in the ancient atmosphere "offset" the decrease in methane concentration. This is the reason that eternal ice did not cover the surface of the earth, even though the energy coming from the sun was then only about 88% of its current value.
