A new study published in Nature reveals that ice ages are likely caused by the collision of tectonic plates near the Earth’s equator. The research was headed by scientists from the Massachusetts Institute of Technology (MIT).
The Earth has experienced three ice ages over the last 540 million years, each of which caused global temperature decreases that lead to the production of glaciers and ice sheets which extend outside of the polar caps that they usually inhabit. In the new study, the data shows that before the Earth’s last three major ice ages there were tropical “arc-continent collisions.” Per Phys.org, these collisions occur when oceanic plates pile up over continental plates and expose the oceanic rock underneath of them to the tropical environment.
When the oceanic rock meets the outside environment, the magnesium and calcium in the rock reacts with the carbon dioxide in the atmosphere, sucking the carbion dioxide into the rock, sequestering it into the form of carbonates — like limestone. As Discover Magazine reports, over millions of years, this weathering process sucks enough carbon dioxide out of the atmosphere that temperatures decrease, and glaciers start moving outward from the polar caps.
“We think that arc-continent collisions at low latitudes are the trigger for global cooling,” said Oliver Jagoutz, an associate professor at MIT’s Department of Earth, Atmospheric, and Planetary Sciences. “This could occur over 1-5 million square kilometers, which sounds like a lot. But in reality, it’s a very thin strip of Earth, sitting in the right location, that can change the global climate.”
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Every time an oceanic plate begins to collide with a continental plate, it creates a fault line called a suture. The team looked deep into the data of Earth’s history for other similar collisions in tropical climates, looking for suture zones. Afterward, they used computer modeling to simulate the movement of tectonic plates in these areas, scanning backwards in time.
After analyzing the data, the team found that there were three periods that contained major sutures in the tropics, and each coincided with the three most recent major ice ages: in the Late Ordovician (455 to 440 million years ago), the Permo-Carboniferous (335 to 280 million years ago), and the Cenozoic (35 million years ago to present day). Jagoutz also said that they confirmed that there were no glaciation events — or ice ages — during periods when suture zones were outside the tropics.
“We found that every time there was a peak in the suture zone in the tropics, there was a glaciation event. So every time you get, say, 10,000 kilometers of sutures in the tropics, you get an ice age.”