Tectonic collisions can cause major ice ages

On geological scales, what really controls the climate is not the atmosphere, it's the soil. Most of the Earth's carbon dioxide is underground, in reservoirs of natural gas and oil, but also in the rocks themselves. The tectonic plates of the planet slide against each other and bury the carbon deep in the surface while exposing cool rocks that will absorb more carbon over time.

This carbon can be released during major volcanic events, resulting in massive extinctions. But the process can also work in the other direction, when rocks extract carbon from the sky. A new study by MIT researchers says the last three glaciations of the Earth have been caused by tectonic plate collisions that have brought fresh, carbon-thirsty rocks to the surface. For millions of years, these rocks have sucked enough carbon dioxide from the atmosphere to drop temperatures and send glaciers to the outside of the poles.

The process is simple Most of the Earth's mantle rock is composed largely of silicate and, once exposed to air, will naturally react with carbon dioxide, forming new minerals that will sequester carbon in the form of carbon dioxide. solid. This process is much more likely to occur in the tropics, where temperatures are higher and frequent rains will carry soil to expose bare rocks.

At times in Earth's history, oceanic tectonic plates in the tropics have collided with continental plates, sliding over them and exposing hundreds of thousands of square kilometers of fresh rock in the air. These stacks, called arc-continent collisions, create a generous supply of fresh rocks. The weathering processes begin on contact with the air and, over the course of a few million years, the carbon is gradually drained from the atmosphere.

For their most recent study, published Thursday in Science, MIT researchers first traced the origins of the Himalayas. Although the forbidden mountain range is north of the equator today, it actually formed 80 million years ago in more southerly latitudes as a result of A collision between the supercontinent Gondwana and Eurasia. The birth of the Himalayas proved to have preceded by a few million years the global ice age – a short period in geological terms.

Scientists did the same type of analysis for the remains of other arc-continent collisions in the world and traced their origins back in time. In the end, researchers discovered that they could associate these geological events with three major ice ages over the previous 540 million years. The Ice Age of the late Ordovician (460 to 440 million years ago), Permo-Carboniferous (335 to 280 million years ago) and Cenozoic (there are 35 million years) was preceded by a tectonic activity that is about 6,000 miles long at the surface.

The effects have been drastic in some cases. The Late Orodovian Ice Age killed about 85% of all marine species and saw glaciers sweep over North Africa. The glaciers created by the Permo-Carboniferous would have spread over a circle of 50 degrees of latitude. The Cenozoic Ice Age, in which we still live, is the reason why we are currently seeing ice caps on the poles.

Finally, the carbon stuck in the rocks will reach the mantle of the Earth, where it will be liquefied and returned to the surface by volcanic eruptions. The planet has been both warmer and colder than today, and the natural cycle of our planet that breathes its carbon has been one of the main drivers of these changes.

The difference between the geological cycle of carbon and the warming we see today is, of course, the weather. It takes millions of years for fresh rock to come to the surface and start absorbing carbon. We have warmed the planet noticeably in less than a hundred years. Anyway, there is currently a collision between an arc and a continent in Indonesia – that's probably one of the reasons why we are still technically in an ice age.

Some researchers have suggested that we try to artificially accelerate the process of weathering rocks by grinding silicate-bearing rocks ourselves and spreading them around. However, it is unclear if this process will eventually sequester more carbon than it has created. In addition, grinding thousands of square kilometers of rocks is not an easy task.

In the end, we can not rely on the rocks to save us.