How many mass extinctions were caused by asteroids that hit Earth?

Since the theory that explains how the dinosaurs disappeared was published in 1981, humanity is so clear about the danger posed by meteorites that NASA is testing these days if it can deflect them.

But an asteroid doesn’t always cause an extinction, it doesn’t even depend on how big it is. The key may be on the ground it hits.

The Geological Society of London, the oldest in the world in its discipline, publishes this month in its journal a work by two researchers from the Volcanological Institute of the Spanish Canary Islands (Matthew James Pankhurst and Beverley Claire Coldwell) and one from the University of Liverpool (Christopher Stevenson) on the role that a specific mineral, potassium feldspar (Kfr), plays in the extinction processes caused by meteorites in the Earth’s past.

The authors recall that, at the moment, there are only two meteorite impacts against the Earth that science generally recognizes as having triggered mass extinctions in the last 600 million years: that of Chicxulub, in Mexico, al which is attributed the great extinction of the Cretaceous, occurred 66 million years ago, and that of Acraman, Australia, 580 million years ago.

The most recent of these two cataclysms left a crater in the Yucatan peninsula 85 kilometers in diameter, while the previous one, in the Australian mountains, formed another 51 kilometers.

“That has created the impression that if a specific type of meteorite impact can cause changes on a global scale, it needs to be of extreme size.” the researchers point out, because the extinction mechanism that activates these phenomena is that of the “Impact winter”, the period in which the enormous amount of dust projected by the crash blocks sunlight, stops photosynthesis in plants and changes the planet’s climate.

However, they point out, if that were the case, there would have to be an almost immediate correlation in geological terms between the meteorite collision and the mass extinction of living beings, because post-impact winters are temporary phenomena that generally last less than a year, although the layer of rubble scattered throughout the planet can last for many centuries.

This study analyzes 33 meteorite impacts against the Earth that occurred in times when it already harbored life, including the eleven to which, with greater or lesser acceptance, are attributed with having set in motion processes of mass extinction on the planet.

And their conclusion shows that it is not the size of the asteroid that determined that its collision with the planet led to an extinction. In fact, they have found that some huge meteorite impacts coincided at relatively stable times for life, including the fourth in size in the entire geological record: the one that formed 215 million years ago Lake Manicouagan, in Canada, with 48 kilometers diameter.

On the other hand, smaller impacts appear in the geological record at times when an ecological shift is observed on the planet.

These three researchers highlight that there is an element that is repeated in all the impacts associated with mass extinction processes in the last 600 million years: potassium feldspar, a generally harmless mineral, is abundant in the layers of dust they deposited, but that suspended in the atmosphere, where it is rare to find it under normal conditions, it changes the properties of clouds: it reduces the proportion of solar radiation they reflect, which in turn warms the climate and enhances the greenhouse effect.

And that finding leads them to propose as a model that it is the meteorites that hit soils rich in potassium feldspar that have the capacity to destabilize the climate on a global scale, change the conditions for life on Earth and activate massive extinction processes.

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