Enormous seismic events that took place at the equator are responsible for the plummeting global temperatures that have marked each of Earth’s ice ages, according to a new study.
As the plates of the planet’s crust smashed into each other, they left vast areas of oceanic rock exposed.
Scientists think the high temperatures of the tropics triggered a chemical reaction that led to these rocks sucking massive volumes of CO2 from the atmosphere.
Just as the rising CO2 from human industry is causing global temperatures to rise, removing it has had the opposite effect, bringing temperatures down and triggering ice ages.
Over the course of Earth’s history, the planet has experienced three enormous ice ages – in which glaciers and frozen regions extend far beyond the polar caps – each lasting several million years.
The most recent ice age began 35 million years ago and is still technically on-going, marked by the spread of ice sheets across Greenland and Antarctica.
At the point where two plates collide, they create mountain ranges containing “sutures” – clear fault lines containing newly exposed rock.
Researchers at the Massachusetts Institute of Technology realised the emergence of sutures over the course of millennia coincided with the onset of each major ice age.
They also found that while some sutures, such as the one located in the Himalayas, had over time moved away from the equator, each one had its origins in the tropics.
“We found that every time there was a peak in the suture zone in the tropics, there was a glaciation event,” said Dr Oliver Jagoutz, a geologist at MIT who led the study.
“So every time you get, say, 10,000km of sutures in the tropics, you get an ice age.”
While the reaction of substances like calcium and magnesium in the rocks with CO2 was the starting point for global cooling, it has also had a role in ending each ice age.
Once all the rock that was available to react with the CO2 had been weathered away, it could no longer store any more climate-warming gas, leading to temperatures rising.
Despite the planet currently experiencing a relatively icy period, global temperatures are rising as human activity pumps huge volumes of carbon emissions into the atmosphere.
While employing the planet’s geology to somehow reverse this process seems like an appealing idea, Dr Jagoutz said it is unlikely to be much help.
“The Earth does this in a slow, geological process that has nothing to do with what we do to the Earth today. And it will neither harm us, nor save us,” he said.
These results were published in the journal Science.
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