About 466 million years ago, long before the age of dinosaurs, the earth froze. The oceans began to freeze on the poles of the earth, and the new temperature range around the planet created the conditions for the upswing of new species. The cause of this ice age has been a mystery until now: a new study in Science Advances argues that the ice age was caused by global cooling, triggered by additional dust in the atmosphere caused by a huge outer-space asteroid collision.
There is always a lot of dust floating from space on Earth, small pieces of asteroids and comets, but this dust is usually just a tiny fraction of the other dust in our atmosphere, like volcanic ash, desert dust, and sea salt. But when a 150-kilometer-wide asteroid broke apart between Mars and Jupiter 466 million years ago, it produced far more dust than usual. "Normally, the earth gets 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 newspaper's authors. "Imagine you multiply that by a factor of a thousand or ten thousand." In the few million years after the collision, it would rather ten million semi-finished products.
"Our hypothesis is that the abundance of extraterrestrial dust over a period of at least two million years played an important role in altering the climate on Earth and contributing to the cooling," says Heck.
"Our results show for the first time that such dust has sometimes dramatically cooled the Earth," says Birger Schmitz of the Swedish University of Lund, lead author of the study and researcher at the Field Museum. "Our studies can provide a more in-depth, empirically-based understanding of how this works, and this, in turn, can be used to assess whether model simulations are realistic."
To find out, researchers have searched for traces of space dust 466 million Years old rocks and compared them with tiny micrometeorites from the Antarctic as a reference. "We investigated extraterrestrial matter, meteorites, and micrometeorites in the Earth's sediment record, which means rocks that once were seabed," says Heck. "And then we extracted extraterrestrial matter to find out what it was and where it came from."
Extracting extraterrestrial matter – the tiny meteorites and dust particles from space – involves extracting and treating the old rock with acid that eats up the stone and leaves the room stuff. The team then analyzed the chemical composition of the remaining dust. The team also analyzed rocks from the ancient seafloor, looking for elements that are rare in earth rocks, as well as isotopes – different forms of atoms – that have the hallmarks of coming from outer space. For example, helium atoms normally have two protons, two neutrons, and two electrons, but some that are shot out of the sun into space lack a neutron. The presence of these special helium isotopes together with rare metals, which are common in asteroids, proves that the dust comes from outer space.
Other scientists have already determined that our planet is going through an ice age around this time. The amount of water in the Earth's oceans affects the way rocks form on the sea floor, and the rocks of that time show signs of shallower oceans – a sign that some of the Earth's water is trapped in glaciers and sea ice was. Schmitz and his colleagues are the first to show that this ice age is synchronized with the additional dust in the atmosphere. "The timing seems perfect," he says. The extra dust in the atmosphere helps to explain the ice age – by filtering out the sunlight, the dust would have caused a global cooling.
As the dust floated down to earth for at least two million years, the cooling was gradual enough to adapt to life and even benefit from the changes. An explosion of new species evolved into living beings adapted for survival in regions with different temperatures.
Heck notes that this period of global cooling has proved beneficial to life on Earth, but rapid climate change can be catastrophic. "The global cooling we are looking at is about timescales of millions of years, which is very different from the climate change that was caused 65 million years ago by the meteorite that killed the dinosaurs, and it's different from today's global warming – this global slowdown was a gentle push and there was less stress. "
It is tempting to believe that today's global warming could be resolved by replicating the dust shower that triggered global cooling 466 million years ago , But Heck is cautious: "Geo-engineering proposals should be evaluated very critically and very carefully because if things go wrong, things could get worse than before."
Although Heck is not convinced that we found the solution As far as climate change is concerned, it is a good idea to think in that direction.
"We are experiencing global warming, that's undeniable," says Heck. "And we need to think about how we can prevent or minimize catastrophic consequences. Every reasonable idea should be investigated.
This study was written by scientists from the Field Museum, the University of Chicago, Lund University (lead), the California Institute of Technology, the Vriije Universiteit Brussel, Ohio State University, Université Libre de Bruxelles, Russian Academy of Sciences, Federal University Kazan, Royal Belgian Institute of Natural Sciences, Durham University, Chinese Academy of Sciences, Center for Comparative Paleontology China, ETH Zurich, Natural History Museum St. Gallen Switzerland and Woods Hole Oceanographic Institution.