A meteorite impact caused a snowball to land on Earth

A meteorite impact caused a snowball to land on Earth

Frozen landscapes as far as the eye can see, average temperatures of -60°C: these conditions are hard to imagine today. However, the Earth has experienced several periods when it was almost completely covered in ice. During the Cold Age (between 720 and 635 million years ago), our planet experienced at least two “snowball” Earth episodes. But how were these extreme events triggered? Various reasons have been proposed: low insolation in this period (about 6%), and continental erosion that would have consumed part of the carbon dioxide (CO).2) the atmosphere, reducing the effect of climate warming, or even releasing volcanic aerosols into the atmosphere. If these mechanisms contributed to the creation of such ice clusters, they were undoubtedly not the causative elements, according to Minmin Fu, from Yale University in the US, and his colleagues, who have discovered a new way to explain snowball events. :Meteor impacts.

When a large enough meteorite hits Earth, in the right location (a carbonate platform for example), the impact releases sulfur aerosols (SO2) and dust in the stratosphere. These particles increase the albedo of the Earth's atmosphere, that is, the amount of solar energy reflected by the atmosphere before it reaches the surface, causing the average temperature to fall: we speak of the “winter effect”. This is what happened 66 million years ago, at the end of the Cretaceous period, when a meteorite struck what is now Mexico, leading, among other things, to the extinction of non-bird dinosaurs.

To assess the impact of a meteorite impact on the creation of a snowball Earth, Minmin Fu and his colleagues used a numerical climate model, with different initial conditions corresponding to different eras: the pre-industrial era (about 300 parts per million, ppm, from2), last glacial maximum 21,000 years ago (190 ppm CO22), Cretaceous (about 1140 ppm CO22), refrigerant (1500 ppm or 750 ppm CO22, but with 6% less insolation). For each series of initial conditions, the researchers developed three SO release scenarios.2 Associated with a meteorite impact: 6.6, 200 (most plausible) and 2000 gigatonnes of sulfur dioxide2.

In most scenarios, the team of scientists observed a significant increase in sea ice extent within a few years. In many cases (pre-industrial, Cretaceous, Cryogenic at 1500 ppm CO22…) All this ice soon ends up retreating. But in scenarios with at least 200 gigatons of sulfur dioxide2simulating the last glacial maximum and cold at 750 ppm CO22 An almost complete ice cover appears to form on the Earth's surface in just one decade, with ice thickness reaching more than 10 meters at the equator. These results suggest that under cold enough initial conditions (and only under these conditions), a falling meteorite could theoretically create a snowball Earth — without being sufficient in itself.

According to the researchers, the probability of an object of sufficient size colliding in a location to release aerosols over the past 2.5 billion years is 53%. At present, no trace of the meteorite impact has been found at the time of the Snowball Earth events, and even if such an impact occurred, the crater it created would certainly have disappeared due to erosion or plate tectonics. But some evidence could confirm this scenario, such as a small amount of glacial deposits associated with high speed ice formation, or large concentrations of iridium in sedimentary deposits that formed at that time.

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