Geologists at the Massachusetts Institute Of Technology (MIT) claim that massive tectonic collisions that occurred near the Earth’s equator could have caused two ice ages, 80 million and 50 million years ago. The tectonic collisions exposed rocks that absorbed carbon dioxide from the atmosphere as well as buried volcanoes which released gases like carbon dioxide and increased global temperature.
Their study, published on April 18 in the journal Proceedings of the National Academy of Sciences, states that the equator is a tropical zone where rocks such as basalts and ultramafic rocks undergo heavy weathering due to high heat and frequent rain. This causes a chemical reaction that enables these rocks to absorb carbon dioxide, a process also known as silicate weathering. The significant absorption of carbon dioxide from this activity was what cooled the atmosphere millions of years ago.
Additionally, 90 million years ago, tectonic activity caused the northeastern edge of the African plate to crash and slide under the oceanic plate in the Neo-Tethys Ocean, an ancient body of water lying between the supercontinents Gondwana and Eurasia. Consequently, this created a chain of volcanoes which released gases that heated up the planet.
However, the oceanic plate got pushed up and exposed ocean rocks including the carbon-absorbing basalt and ultramafic rocks as well as obliterated the volcanoes as the African plate kept moving north 80 million years ago. The same consequences happened in a second collision 50 million years ago when India merged with Eurasia.
As a result, carbon dioxide levels were greatly reduced during these two periods since the gas got absorbed by the exposed rocks and was no longer replenished by the obliterated volcanoes, causing the two ice ages.
The research team analysed the rocks and quantified the amount of carbon dioxide in the atmosphere between 100 million through 40 million years ago. The results confirmed that atmospheric carbon dioxide was greatly reduced at the same time the two collisions happened 80 million and 50 million years ago. Carbon dioxide levels also reflected ocean temperatures at these times.
They say that the same thing is happening today near the island of Java. The tectonic activity aforementioned is also pushing the Australian plate north, exposing basalts. However, they point out that this present-day process is comparably smaller.