MIT: ‘Snowball Earth’ Came From Huge Drop in Sunlight

ice sheet. Credit: Stephen Hudson / CC BY 2.5 https://en.wikipedia.org/wiki/Antarctic_Plateau#/media/File:AntarcticaDomeCSnow.jpg

The last ice age on Earth ended about 11,000 years ago, but that was just a few flurries compared to so-called Snowball Earth scenarios. Scientists believe Earth experienced several of these periods when the entire surface was covered by ice and snow. New research from MIT points to a potential mechanism for Snowball Earth events, and that could help explain the development of complex life. It may also impact the search for exoplanets around other stars. 

An ice age is simply a period during which global temperature drops sufficiently for polar ice caps and alpine glaciers to expand. A Snowball Earth is on a completely different level, and that’s made it difficult to identify causes. Researchers have long assumed that it has something to do with a reduction in incoming sunlight or drop in retained global heat, but the MIT team points specifically to “rate-induced glaciations” as the primary cause. 

The findings suggest that all you need for a Snowball Earth is a sufficiently large drop in solar radiation reaching the planet’s surface. Interestingly, the modeling done by graduate student Constantin Arnscheidt and geophysics professor Daniel Rothman show that solar radiation doesn’t have to drop to any particular threshold to trigger a Snowball Earth. Rather, it just needs to drop quickly over a geologically short period of time. 

When ice cover increases, the planet reflects more light and the glaciation becomes a “runaway” effect. That’s how you get to a Snowball scenario, but luckily for us, these periods are temporary. The planet’s carbon cycle is interrupted when ice and snow cover the entire surface, and that causes a build-up of carbon dioxide. Eventually, this leads to a warming trend that breaks Earth out of a snowball period. 

The research suggests a few ways solar radiation could decrease fast enough to trigger global glaciation. For example, volcanic activity could deposit particles in the atmosphere that reflect sunlight before it reaches the surface. It’s also possible that biological processes could alter the atmosphere, producing more cloud cover to block the sun. 

The two suspected snowball Earth periods most likely happened around 700 million years ago, which is a notable time in the planet’s history. That’s also when multicellular life exploded in the oceans. So perhaps, Snowball Earth cleared the way for the development of complex life. It might be the same on other planets, too. We may eventually spot exoplanets around distant stars in the “habitable zone” covered in ice. That doesn’t mean they’ll be icy forever, and big things could be coming as they thaw.

Top image credit: Stephen Hudson/CC BY 2.5

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