Tectonics in the Tropics Trigger the Ice Ages on Earth

Scientists have figured out the likely trigger for the three ice ages, which occurred in the last 540 million years.

The term ‘Ice Age’ refers to a period during which global temperatures fall drastically to produce extensive glaciers and ice sheets that stretch well beyond their polar caps. According to a recent study, tectonics in the tropics are the likely triggers for these ice ages. A phenomenon, known as ‘Arc-continent Collisions’, is held responsible for these extremely cold periods as they expose tens of thousands of kilometers of oceanic rock to a tropical environment. Basically, oceanic plates rode up over continental plates during this process, following a series of tectonics near the Equator of the planet. Olivier Jagoutz, an Associate Professor in the Department of Earth, Atmospheric, and Planetary Sciences at MIT, talked about that and said,

“We think that arc-continent collisions at low latitudes are the trigger for global cooling. 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.”

The researching team proposed that the heat and humidity of the tropics could be the reason which triggers a chemical reaction between the atmosphere and the rocks. They specifically mentioned that Magnesium and Calcium can pull out Carbon Dioxide permanently from the atmosphere by reacting with the greenhouse gas. When this process continues to occur over millions of square kilometers, sufficient Carbon Dioxide is extracted from the atmosphere to cause cooling at a global scale. This ultimately leads to extreme spells of low temperatures called ‘Ice Ages’.

Sutures and Ice Ages

The suture is a fault zone along which the continental and oceanic plates collide. A number of mountain ranges, including the Himalayas, have several sutures that have migrated from their original positions over a period of millennia. The researching team of Jagoutz observed two sutures of the Himalayas in 2016 and found that both of them have a common tectonic migration. One of them was created 80 million years ago when Gondwana (supercontinent) moved north while the second suture is around 50 million years old.

On both occasions, global atmospheric cooling events preceded the arc-continent collisions by millions of years and they occurred in tropical zones near the equator. Researchers analyzed the rate of reaction between Carbon Dioxide and Ophiolites (oceanic rocks) to conclude that both of these sutures could have eliminated enough gas from the atmosphere to trigger the corresponding ice ages. Surprisingly, it was found that the same process is likely responsible for ending these ice ages as the oceanic rock erodes away with time and the new rock doesn’t consume that much Carbon Dioxide. Jagoutz referred to that in the following words:

“We showed that this process can start and end glaciation. Then we wondered, how often does that work? If our hypothesis is correct, we should find that for every time there’s a cooling event, there are a lot of sutures in the tropics.”

Confirmation of the Hypothesis

In order to be certain about their theory, the researching team performed an extensive study to figure out the locations of all the major suture zones on Earth. Once their data was complete, they used a computer simulation to reconstruct the movement of continental and oceanic plates and these suture zones. This journey towards the past allowed them to determine the origin of these sutures. It was observed that major sutures were formed (in the tropics) in three different phases in the last 540 million years and all of these periods coincided with one of the famous ice ages. Similarly, simulations showed that no ice ages were possible when major suture zones were outside of the tropics. Jagoutz acknowledged that by saying,

“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.”

The study published in the journal ‘Science’ also revealed that a major suture zone, which is spanning over an area of about 10,000 kilometers, is still active today in Indonesia. Jagoutz suggested that it is very much possible that the appearance of extensive ice sheets at the poles could be an indication of another ice age.