Astronomers Have Linked The First Global Glaciation Of The Earth With The Long-Term Dimming Of The Sun
Astronomers have found that glaciers completely covered the Earth several times over the past billion years since, for a relatively long time, the amount of light entering the Earth was sharply reduced. The results of their research are available in the scientific journal Royal Society Proceedings A.
"Our calculations show that if the brightness of the Sun's light decreases by only 2% for about 10 thousand years, this will be enough to change the climate of the planet in such a way that its entire surface will be covered with ice. It is reasonable to assume that the cause of such episodes in the history of the Earth could be similar events, " said one of the authors of the work, a planetary scientist from the Massachusetts Institute of Technology (MIT), Konstantin Arnscheidt.
Over the past 3 billion years, the Earth has experienced several dozen collisions with fairly large small celestial bodies. Geologists and planetary scientists are actively studying their consequences – giant craters and mass extinctions of animals and plants.
Besides, scientists have recently found some evidence that at least one of the mass animal extinctions that occurred at the end of the Ordovician period may have occurred not because of the fall of a large meteorite, but because of the collision of two relatively large asteroids in the vicinity of Mars. Because of this event, the inner regions of the Solar system were filled with a large amount of dust. As a result, the Earth began to receive much less heat and light from the Sun, and the climate of our planet became sharply colder.
Arnscheidt and his colleague Daniel Rothman, a professor at MIT, tried to figure out how strong the Sun must dim to turn the Earth into an icy planet. Similar events have already occurred in the history of the Earth about 700 and 650 million years ago, when glaciers covered almost the entire planet, and on its equator formed sedimentary rocks typical of modern circumpolar regions.
The planet's energy budget
Average temperatures on the surface of any planet, including the Earth, depend on how much heat and energy it receives from the star and generates on its own, as well as how quickly it radiates heat back into space. Both of these parameters depend on many natural factors, including the proportion of greenhouse gases in the atmosphere and the star's activity cycles.
Scientists have long noticed that the rate of change in these parameters strongly affects how the Earth's climate changes under the influence of shifts in the amount of heat received or produced by it, as well as how much of it escapes into space. As a rule, the faster such changes occur, the more the climate changes.
Based on similar considerations, Rothman and Arnscheidt calculated how a sharp decrease in the amount of heat from the Sun would affect the Earth's climate. To do this, they developed a simple mathematical model that can be used to calculate the effects of rapid and slow shifts in the level of solar radiation, as well as other factors that affect the amount of heat entering and leaving the planet.
These calculations unexpectedly showed that if the rate of such changes is high enough, even an imperceptible decrease in the amount of solar energy reaching the Earth will cause a radical cooling of its climate and lead to the transformation of the planet into a kind of "ice ball." In particular, it is enough to reduce the amount of incoming heat by only 0.3% for about 40 thousand years, or 2% for 10 thousand years.
Such shifts in the amount of incoming heat, as noted by planetary scientists, are so small in scale that they could be caused not only by asteroid collisions in the inner Solar system but also by various natural processes on the planet itself. In particular, such a role could be played by aerosols and particularly dense clouds that occur as a result of volcanic emissions. Their source could even be the life activity of the first algae.
Scientists cannot yet say which of these scenarios is closer to the truth since the speed of changes in the level of solar illumination of the Earth's surface can not yet be calculated. Further work and an analysis of how quickly past global glaciations occurred, Rothman and Arnscheidt hope, will provide an accurate answer to this question and help understand why glaciers subsequently retreated.