750 million years ago, glaciers reached the equator
Christian Galya, Le Monde
Geologists have long been intrigued by the presence of traces of very ancient glaciers in many parts of the world, including at the equator. What is their age? From 800 to 550 million years — the end of the Proterozoic era. In 1998, based on the accumulated knowledge of science in the field of tectonics and mechanisms of climate change, Paul Hoffman and Daniel Schrag (Harvard University) have put forward the hypothesis that during this period the globe many times covered with a thick layer of ice. This is the famous theory of "Earth — the snowball" (Snowball Earth).
What could have caused this phenomenon? The Franco-American team of scientists led by Yannick Donnade, climatologist from the French National Centre for Scientific Research (CNRS), offers on the pages of the journal Nature on 18 March script, built on the basis of the new model.
The results of research funded by the program CNRS Eclipse (Environment, the ancient climate, history and evolution), show that "the glaciation of the Earth was caused by a significant decrease in the amount of carbon dioxide in the atmosphere." It, in turn, was the result of "the collapse of the supercontinent Rodinia, the center of which was then located in the equatorial zone, and which extended from 60 degrees north to 60 degrees south latitude," says physicist at CNRS Yves Godderi working in Toulouse.
Rodinia, tell scientists began to fall apart 800 million years ago, under the influence of "hot spots" — a kind of igneous emissions, break the crust on the surface and throws a lot of lava. This was followed by the expansion of the oceans and seas, resulting in the increased amount of vapor in the atmosphere, and hence the rain. The carbon is in the cloud in the form of carbon dioxide, soon found himself in the ocean: it firmly, "sat down" in the sediments in the form of carbonates.
At the same time, the giant lava flows caused by splitting the motherland, formed on the surface of the continents basalt surface. The latter "consume eight times more carbon than the same area on the granite surface, eroding under the influence of moisture," — said Yves Godderi.
All of these processes, which lasted 30-40 million years old, have significantly reduced the amount of CO2 in the atmosphere. This led to a lowering of the average surface temperature of 8 degrees. Glaciers reached 30 degrees latitude, and the surface was reflected in the space even more sunlight. Then, about 750 million years ago, "ice down to the equator, the average temperature of the globe has dropped to -40 degrees (-20 — at the equator, -80 — at the poles)," — said the scientist.
Fortunately for life on the planet, the Earth itself is not stayed. Despite the ice, volcanic activity continued to emit CO2. Climate soon became very hot: the average temperature rose to 25-30 degrees. This scenario allows us to understand why these glaciers are not repeated in the future. The fact is that the newly formed a continent no longer had exclusive equatorial configuration.