March 1, 2024

An asteroid may have turned ancient Earth into a snowball

If you were to travel back in time many millions of years, Earth would look like the planet Hoth of Star Wars: Frigid, dry air would sweep across a world of endless ice, covering nearly every inch of land and sea. This state of global refrigeration, known as Snowball Earth, has happened at least twice, both times more than 600 million years ago. And something must have gone wrong with the world’s thermostat to turn it into a giant ball of ice – but what?

Various ideas, from rogue volcanism to supercontinental destruction, have been suggested. A new study, published today in Science Advancesexplores another idea that has been largely ignored: the cataclysmic impact of an asteroid.

When large asteroids hit the planet, they can release large amounts of rock and send it skyward. Much of this ejected material may be composed of sulfur-containing minerals, which become aerosols that reflect sunlight into the stratosphere, the layer of the atmosphere above the lowest. Get enough aerosols up there and Earth can get very cold extremely quickly.

For this new study, scientists simulated the injection of sulfate aerosols into the stratosphere at varying concentrations — the kind generated by a massive asteroid strike — at various points during Earth’s past, from its extremely hot eras to its already-expanded chapters. cold. They found that warmer climates could withstand the brunt of an asteroid impact without freezing, but already cold climates could be pushed into a snowball state by an extraterrestrial punch.

There is currently no geological evidence to show this happened. But this study shows that asteroids should be viewed as potential suspects. “It’s a very interesting thought experiment,” says Thomas Gernon, a geoscientist at the University of Southampton who was not involved in the study.

It’s also a study that makes you appreciate current efforts to develop a planetary defense system – a system that combines asteroid spy observatories and asteroid diversion technologies to ensure that dangerous asteroids never reach the planet’s doorstep.

“The effects of a major impact followed by global glaciation would be disastrous for complex life and could lead to the extinction of humanity,” says study author Minmin Fu, a climate dynamicist at Yale University.

A force strong enough to remake the Earth

Block sunlight long enough, the planet cools and its icy areas grow. Ice reflects sunlight back into space, so as it receives it, the planet cools further, triggering more ice formation – and if it reaches a certain ice threshold, the planet inexorably becomes a ball. of snow.

While it is unquestionable that during its multibillion-year history the Earth has gone through warmer times and colder times, not all scientists agree that the Earth was completely encased in ice. But a wealth of strange, ancient geological features—for example, crushed layers of sediment and rocky debris, typically created and transported by glaciers, found at the equator—have convinced many people that the Earth has been engulfed in snow and ice at least twice— between 720 and 635 million years ago, during the aptly named Cryogenian period of the Neoproterozoic era.

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Determining why they happened (and why they ended) is of paramount importance; Not long after the second snowball melted, an explosion of complex life occurred, something known as the Cambrian Explosion.

“So it’s critical to understand why they happen – to understand the history of life on Earth and the potential for life on other planets,” says Fu.

Volcanoes have long been considered the prime suspect for snowball formation: perhaps they expelled too much sulfur dioxide (which becomes an aerosol in the atmosphere), generating a cooling effect – or perhaps, another theory suggests, the Earth has already had too much fewer volcanoes spewing carbon dioxide into the atmosphere. sky, reducing the greenhouse effect.

“Both hypotheses are viable,” says study author Alexey Fedorov, an expert in climate modeling at Yale University. But it’s not clear whether volcanoes could erupt such high amounts of sulfur dioxide quickly enough, or experience a dramatic drop in carbon dioxide production, to kickstart Snowball Earth.

An asteroid impact, however, occurs differently. “An impact is a geologically instantaneous event,” says study author Christian Köberl, an impact expert at the University of Vienna. And they are known to quickly release a lot of sulfates into the atmosphere.

The Chicxulub impactor, the 10-kilometer-long asteroid that struck Earth 66 million years ago, caused a series of environmental and climate problems enough to trigger a mass extinction. The sulfate aerosols it created also contributed to years of global cooling and sea ice expansion. This didn’t trigger a snowball state – but, the authors wondered, what if something equally catastrophic happened at other points in Earth’s history?

An extraterrestrial antagonist

To test their asteroid theory, the team created detailed simulations of several chapters of the planet’s past, each with different continental, oceanic and atmospheric arrangements: the pre-industrial temperate era (pre-1850), the frigid Last Glacial Maximum (20,000 years). ago), a warm era similar to the Cretaceous (145 to 66 million years ago) and during the Neoproterozoic era (750 million years ago) – a warmer and a colder recreation.

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They then injected plausible, Chicxulub-like amounts of sulfur dioxide gas into the stratospheres of these time periods—6.6, 200, and 2 billion tons of the substance—and observed what happened. Would a Snowball Earth, defined here as global sea ice coverage of 97%, happen?

A completely frozen world did not occur in the mild pre-industrial and Cretaceous eras under any conditions. But adding 200 billion tons of sulfur dioxide to a colder version of the Neoproterozoic era and the Last Glacial Maximum was enough to see ice cover all the world’s seas in less than a decade.

“It’s much harder to induce a snowball when it’s so warm on Earth,” says Köberl. But this study suggests that when the planet is already cold, “it is possible.”

The only way to corroborate this idea would be if a crater similar in size to that of Chicxulub (170 kilometers in diameter) or the sulfur-rich remains ejected by an impact were found and dated to the beginning of these icy periods. Gernon suspects that even after nearly a billion years of erosive activity by water, volcanism, biology and tectonic mixing, a crater this large could still be found hidden on one of Earth’s continents.

“It’s tempting and your modeling is quite convincing,” he says – but he will remain skeptical until the smoking gun geological evidence is found.

For now, this remains a theoretical exercise. “Impacts don’t explain everything,” says Köberl. “But you still need to keep an open mind,” because this study and events like Chicxulub demonstrate how powerfully asteroids can change Earth’s destiny.

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