Scientists think that Earth turned into a "snowball" at least twice in quick succession around 700 million years ago due to significant and rapid drops in the amount of solar radiation reaching the planet's surface, according to a study.
"Snowball Earth" is a hypothesis referring to periods in our planet's long history when almost its entire surface was covered in snow and ice.
While scientists have proposed several different processes—such as widespread volcanic eruptions that blocked out the sun's rays—to explain how the Earth became a snowball, the exact mechanisms are still being debated.
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Nevertheless, a team of MIT scientists say that whatever triggered the temporary global ice ages most likely would have involved processes that rapidly reduced the amount of solar radiation striking the Earth's surface, according to a study published in the journal Proceedings of the Royal Society A.
The researchers came to their conclusions using a mathematical computer model of the Earth's climate system. This model showed that Earth would have to experience around a two percent drop in the solar radiation it received over a period of 10,000 years to trigger a "snowball" scenario.
"It's reasonable to assume past glaciations were induced by geologically quick changes to solar radiation," Constantin Arnscheidt, lead author of the study from MIT's Department of Earth, Atmospheric and Planetary Sciences, said in a statement.
A section of the West Antarctic Ice Sheet with mountains is viewed from a window of a NASA Operation IceBridge airplane on October 31, 2016 in-flight over Antarctica.A section of the West Antarctic Ice Sheet with mountains is viewed from a window of a NASA Operation IceBridge airplane on October 31, 2016 in-flight over Antarctica.Mario Tama/Getty ImagesEven though the exact triggers of a snowball Earth are still contested, researchers generally assume that the process would have involved a "runaway" ice-albedo feedback effect.
Ice and snow has a higher albedo than open water or land—which are darker in color—meaning they reflect more solar radiation. In a situation where the incoming light from the sun was significantly reduced, the extent of Earth's ice would increase.
This would make the planet more reflective overall, leading to more cooling and further ice expansion, eventually becoming an unstoppable process that resulted in a snowball Earth.
One of the proposed mechanisms for the rapid drop in solar radiation reaching Earth's surface is widespread volcanic eruptions that emitted so much material into the atmosphere that sunlight was blocked around the world.
Another explanation is that primitive algae emitted vast quantities of substances into the atmosphere that enabled the formation of widespread, light-reflecting clouds.
Even though a snowball Earth is not likely to be triggered any time soon given the rate at which the world is warming, Arnscheidt said the latest results should teach us "that we should be wary of the speed at which we are modifying Earth's climate, not just the magnitude of the change."
