Major tectonic collisions near the equator have caused three ice ages in the last 540 million years — ScienceDaily

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In the past 540 million years, the Earth has passed through three major ice ages – the period of global temperature dips, producing a large number of ice sheets and glaciers that have surpassed the polar ice sheets.

Scientists at the Massachusetts Institute of Technology, the University of California at Santa Barbara and the University of California at Berkeley have identified possible triggers for these ice ages.

In a study published in Science the research team reported that tropical “arc-land collisions” occurred in each of the three major ice ages – structures occurring near the Earth’s equator Stacked, which ocean plates are driving on the continental plate, exposing tens of thousands of kilometers of marine rock to the tropical environment.

Scientists say that heat and humidity in the tropics may trigger a chemical reaction between the rock and the atmosphere. Specifically, the calcium and magnesium of the rock react with carbon dioxide in the atmosphere, drawing the gas out of the atmosphere and permanently sequestering it in the form of carbonates such as limestone.

Over time, the researchers say that this weathering process takes place in the millions of square kilometers and absorbs enough carbon dioxide from the atmosphere to cool the world and eventually set off the ice age.

"We believe that curved continental collisions at low latitudes are triggers for global cooling," said Oliver Jagoutz, associate professor of earth, atmosphere and planetary science at the Massachusetts Institute of Technology. “This can happen in more than 1-5 million square kilometers, which sounds a lot. But in fact, it is a very thin earth, located in the right place, can change the global climate.”

Jagoutz co-authors are Francis Macdonald and Lorraine Lisiecki of the University of California, Santa Barbara, and Nicholas Swanson-Hysell and Yuem Park of the University of California at Berkeley.

Tropical Trigger

When the ocean plate approaches the continental plate, the collision usually produces a series of newly exposed rocks. The fault zone where the ocean and continental plates collide is called a "stitch." Today, the seams contained in certain mountains, such as the Himalayas, have migrated from the original collision point because the continent has been transferred for thousands of years.

In 2016, Jagoutz and his colleagues reviewed the movements of the two sutures that make up the Himalayas today. They found that both sutures originated from the same structural transport. Eighty million years ago, as the supercontinent known as Gondwana moved northward, part of the land was crushed by Eurasia, revealing long ocean rocks and forming the first suture; 50 million years Before, another collision between the supercontinents caused a second stitch.

The team found that both collisions occurred in the tropics near the equator and occurred millions of years before the global atmospheric cooling event – almost instantaneously on geological time scales. After investigating that exposed oceanic rocks (also known as ophiolites) may react with carbon dioxide in the tropics, the researchers concluded that, given their location and size, the two sutures could indeed sequester enough carbon dioxide to cool the atmosphere. . Trigger the Ice Age.

Interestingly, they found that this process may also be the reason for ending the Ice Age. For millions of years, ocean rocks that can be used to react with the atmosphere are eventually eroded, replaced by new rocks that absorb less carbon dioxide.

"We found that this process can begin and end glacier action," Jagoutz said. "Then we want to know how often this happens? If our assumptions are correct, we should find that there are cooling events every time, there will be a lot of stitching in the tropics."

Exposing the seam of the earth

The researchers looked at whether the more late glacial periods in Earth's history were related to similar arc-shaped continental collisions in the tropics. They conducted extensive literature searches to compile the locations of all major sutures on Earth today, and then used computer simulations of plate tectonics to reconstruct the motion of these sutures, as well as the continent's continental and oceanic plates over time. In this way, they are able to accurately determine the location and time at which each suture is initially formed, as well as the time each suture is stretched.

They identified three of the past 540 million years, in which a major suture of approximately 10,000 kilometers was formed in the tropics. Each of these periods is associated with three famous Ice Ages in the Late Ordovician (455 to 440 million years ago), the Carboniferous Permian (335 to 280 million years ago) and the Cenozoic (35 million years). Consistent. Previously until now). Importantly, they found no glacial or glacier events during the main suture zone formed outside the tropics.

"We found that glacier events occur every time there is a peak in the suture zone in the tropics," Jagoutz said. “So every time you get a 10,000-km suture in the tropics, you will encounter the Ice Age.”

He pointed out that a major suture zone spanning about 10,000 kilometers is still active today in Indonesia, probably the cause of the current glacial and polar ice formations on Earth.

This tropical region includes some of the world's largest ophiolites and is currently one of the most effective areas for the absorption and sequestration of carbon dioxide on Earth. As human-sourced carbon dioxide causes global temperatures to rise, some scientists have proposed grinding large amounts of ophiolite and spreading minerals throughout the equatorial zone to accelerate this natural cooling process.

But Jagoutz said that the act of grinding and transporting these materials may produce additional, unintentional carbon emissions. It is unclear whether these measures will have any significant impact on our life cycle.

"It is a challenge to make this process work on human time scales," Jagoutz said. “The earth does this in a slow geological process, which has nothing to do with what we do today on the earth. It will neither harm us nor save us.”


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