The last ice age on Earth ended about 11,000 years ago, but that was just a few gusts compared to the so-called Snowball Earth scenarios. Scientists believe that Earth experienced several of these periods when the entire surface was covered in 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 can also affect the search for exoplanets around other stars.
An ice age is simply a period during which the global temperature drops enough for the ice caps and alpine glaciers to expand. A snowball Earth is on a completely different level, and that makes it difficult to identify causes. Researchers have long assumed it has something to do with a reduction in incoming sunlight or a drop in retained global heat, but the MIT team specifically points to “frequency-induced glaciations” as the primary cause.
The results suggest that all it takes for a Snowball Earth is a sufficiently large drop of solar radiation to reach the planet’s surface. Interestingly, modeling by graduate student Constantin Arnscheidt and geophysics professor Daniel Rothman shows that solar radiation does not have to fall to any particular threshold to trigger a Snowball Earth. Rather, it only needs to fall rapidly in a geologically short period of time.
When the ice sheet increases, the planet reflects more light and the glaciation becomes a “runaway” effect. This is how you get to a Snowball stage, but luckily for us, these periods are temporary. The planet’s carbon cycle is interrupted when ice and snow cover the entire surface, causing an accumulation of carbon dioxide. Ultimately, this leads to a warming trend that brings Earth out of a snowball period.
The research suggests some ways that solar radiation could decrease fast enough to trigger global ice age. For example, volcanic activity could deposit particles in the atmosphere that reflect sunlight before it reaches the surface. It is also possible that biological processes alter the atmosphere, producing more cloud cover to block the sun.
The two suspicious periods of snowballing on Earth probably occurred about 700 million years ago, which is a remarkable moment in the planet’s history. It is also when multicellular life exploded in the oceans. Then, perhaps, Snowball Earth cleared the way for the development of complex life. It could also be the same on other planets. Eventually we can detect exoplanets around distant stars in the ice-covered “habitable zone”. That doesn’t mean they’ll be frozen forever, and great things could come as they thaw.
Top image credit: Stephen Hudson / CC BY 2.5
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