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This is an illustration of the collision of giant asteroids in the space that produced the dust that led to an ice age on Earth. Credit: (c) Don Davis, Southwestern Research Institute
About 466 million years ago, well before the age of the dinosaurs, the Earth froze. The seas have started to frost at the Earth's poles and the new temperature range around the planet has paved the way for a boom of new and evolving species. The cause of this ice age was a mystery, until now: a new study in Progress of science argues that glaciation was caused by global cooling, caused by additional dust in the atmosphere resulting from a collision of giant asteroids in the space.
There is still a lot of space dust floating on the Earth, small bits of asteroids and comets, but this dust normally represents only a tiny fraction of the other dust in our atmosphere, such as volcanic ash. , desert dust and sea salt. But when a 150 km wide asteroid between Mars and Jupiter shattered 466 million years ago, it created much more dust than usual. "Normally, Earth earns about 40,000 tons of extraterrestrial material each year," says Philipp Heck, curator at the Field Museum, associate professor at the University of Chicago, and one of the authors of the journal. "Imagine that you multiply that by a factor of one thousand or ten thousand." To contextualize this, in a typical year, a thousand interplanetary dust semi-trailers fall on Earth. In the few million years after the collision, it would be rather ten million half-points.
It is a 466 million year old fossil meteorite created during the same collision of asteroids that caused the dust that led to an ice age. At the top of the photo is the fossil of a creature resembling a squid, called nautiloid. Credit: (c) Field Museum, John Weinstein
"Our hypothesis is that large amounts of extraterrestrial dust over a period of at least two million years have played a significant role in changing Earth's climate, thus contributing to cooling," says Heck.
"Our results show for the first time that such dust has sometimes cooled the Earth dramatically," says Birger Schmitz of the Swedish University of Lund, lead author of the study and research associate at the Field Museum. "Our studies can provide a more detailed, empirical understanding of how this works, and it can also be used to assess whether model simulations are realistic."
To understand it, the researchers searched for traces of space dust in rocks 466 million years old and compared them to tiny micrometeorites of Antarctica. "We studied extraterrestrial matter, meteorites and micrometeorites, in the sedimentary record of the Earth, that is, rocks that were once seabed," Heck explains. "And then we extracted the extraterrestrial material to find out what it was and where it came from."
These are cliffs made of sedimentary rock that was once an ancient seabed. The gray horizontal line in the rock indicates where the dust of the collision between asteroids has fallen. Credit: (c) Field Museum, Philipp Heck
To extract extraterrestrial matter – tiny meteorites and dust from outer space – is to take the old rock and treat it with acid who gnaws the stone and leaves the space thing. The team then analyzed the chemical composition of the remaining dust. The team also analyzed the rocks of the old ocean floor and looked for elements that rarely appear in the Earth's rocks and isotopes – different forms of atoms – that testify to the fact that they come from outer space. -atmospheric. For example, helium atoms normally have two protons, two neutrons and two electrons, but some neutrons are derived from the Sun and in space. The presence of these special isotopes of helium, as well as rare metals often found in asteroids, proves that the dust comes from space.
Other scientists had already established that our planet was going through an ice age at that time. The amount of water in the Earth's oceans influences the formation of rocks on the seabed. The rocks of this time show shallow ocean signs – an indication of the fact that water from the Earth was imprisoned in glaciers and sea ice. Schmitz and his colleagues are the first to show that this ice age is synchronizing with the extra dust in the atmosphere. "The moment seems perfect," he says. The extra dust in the atmosphere helps to explain the ice age: by filtering the sunlight, the dust would have caused global cooling.
Since the dust has floated on the Earth for at least two million years, the cooling has been progressive enough for life to adapt and even benefit from the changes. An explosion of new species evolved as creatures adapted to survival in regions with different temperatures.
Heck notes that while this global cooling period has proven to be beneficial for life on Earth, rapid climate change can be catastrophic. "In the global cooling we have studied, we are talking about time scales of millions of years. It's very different from the meteorite-induced climate change that killed the dinosaurs 65 million years ago, and it's different from global warming today – this global cooling has been a boost. There was less stress. "
It is tempting to think that today's global warming could be solved by reproducing the cloud of dust that triggered the cooling of the planet 466 million years ago. But Heck says it would be cautious: "The geo-engineering proposals need to be evaluated very critically and very cautiously, because if something goes wrong, things could get worse than before."
Although Mr Heck is not convinced that we have found the solution to climate change, he thinks it is a good idea for us to think that way.
"We are facing global warming, it's undeniable," says Heck. "And we need to think about how to prevent or minimize catastrophic consequences. Any reasonable idea must be explored. "
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Scientists from the Field Museum, the University of Chicago, Lund University (director), the California Institute of Technology, the Vriije Universiteit Brussel, the State University of Ohio, the Free University of Brussels, the Russian Academy of Sciences and the Federal University of Kazan participated in this study. , Royal Belgian Institute of Natural Sciences, University of Durham, Chinese Academy of Sciences, Center of Excellence in Comparative Paleontology of China, ETH Zurich, Naturmuseum St. Gallen Switzerland and Woods Hole Oceanographic Institution.
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