News Space 19 September 2019

Asteroid breakup may have triggered an ice age

Researchers find tell-tale dust among the rocks. Richard A Lovett reports.

A mid-Ordovician limestone section studied at Kinnekulle in Sweden.

Birger Schmitz

An asteroid smashup 466 million years ago appears to have triggered an ice age on Earth, scientists say.

Not that the asteroid struck the Earth, like the one 400 million years later that is widely believed to have killed off the dinosaurs.

Rather, this crack-up occurred far out in the Asteroid Belt, instantly reducing a giant asteroid, probably 150 kilometres in diameter, to rubble.

“This is the largest asteroid breakup that we know of in the past two billion years,” says Birger Schmitz, an astrogeobiologist at Lund University, Sweden, and lead author of a study in the journal Science Advances.

Years ago, his team found evidence that the Earth was affected by this asteroid’s breakup when they found a layer of coin-sized “fossil” meteorites originating from it. But now, they have sifted through the same rock layers for outer-space dust too small to have previously been noticed.

Not surprisingly, the dust turned out to be chemically similar to the fossil meteorites, indicating that it came from the same source.

It also turned out to coincide with a time when sea levels were dropping, an indication that – in the reverse of what’s happening today – glaciers were growing. “This sea-level fall relates to the development of a major ice age,” Schmitz says.

Normally, meteorite dust accounts for only about 1% of the dust in the Earth’s atmosphere, says Schmitz’s co-author, Philipp Heck, a cosmochemist at the Field Museum of Natural History in the US.

But for two million years after the asteroid breakup, he says, it rose by a factor of 10,000 – more than enough to reduce the amount of sunlight reaching the Earth’s surface.

At the same time, dust from the collision would have found its way inside the Earth’s orbit, blocking the amount of sunlight reaching us in the first place.

Unlike today’s climate change, however, this one occurred over the course of a couple of million years. The result, therefore, wasn’t a mass extinction, but an evolutionary kick in the pants for life to adapt, something that occurred in an epoch called the Great Ordovician Biodiversification Event (GOBE).

“It’s very different from the climate change caused by the meteorite 65 million years ago that killed the dinosaurs, and it’s different from the global warming today,” Heck says. “This was a gentle nudge. There was less stress.”

Other scientists are impressed.

“It seems reasonable to have lots of dust arrive on Earth from this event,” says Humberto Campins, a planetary scientist from Central Florida University, US. “I like this paper.”

Melinda Hutson, curator of the Cascadia Meteorite Laboratory at Portland State University, US, agrees.

The smash-up of the 150-kilometre asteroid was well known, she says, as are the fossil meteorites. But, “I hadn’t thought about the amount of dust that would be produced, and its effect on sunlight in the inner solar system,” she says.

“The authors had to have a good combination of background specialties to put this all together.”

As an aside, she notes that the effects might well have spread beyond the Earth. “I found myself wondering if Mars experienced any noticeable climate change,” she says.

Though she adds, “sadly we’re not close to having the kind of data we need to look at this scale of climate change on Mars.”

Contrib ricklovett.jpg?ixlib=rails 2.1
Richard A. Lovett is a Portland, Oregon-based science writer and science fiction author. He is a frequent contributor to COSMOS.
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