Ancient, cataclysmic asteroid collision could inspire climate geoengineering

19 Sep 2019

An illustration of a giant asteroid collision in outer space that produced the dust that led to an ice age on Earth. Image: Don Davis/Southwest Research Institute

The unexpected discovery of an ancient asteroid collision in the solar system may inspire new methods of tackling the climate crisis.

A gigantic asteroid collision in space 470m years ago, which caused dramatic changes to life on Earth, could offer clues on how to tackle the climate crisis, new research suggests. The cosmic crash, which occurred in the asteroid belt between Jupiter and Mars, filled the entire inner solar system – which includes Mercury, Venus, Earth and Mars – with large quantities of dust, triggering an ice age and setting the stage for new species to evolve.

In the study published in the journal Science Advances, researchers say their “unexpected discovery” could be a step towards exploring different artificial methods to cool the planet if current approaches to reduce carbon dioxide emissions prove unsuccessful.

Scientists had already established that Earth was undergoing an ice age around this time but its cause remained a mystery. After analysing traces of space dust in ancient rocks from that time period, an international team of experts believe that the cooling was caused by enormous amounts of debris in the atmosphere from the collision.

While there are space particles – made up of tiny bits of asteroids and comets – constantly floating down to Earth, they make up only a tiny fraction of the dust present in the atmosphere, which also includes debris from deserts, sea salt and volcanic ash.

Scanned image of the ancient fossil meteorite.

A 466m-year-old fossil meteorite created in the same asteroid collision that caused the dust that led to an ice age. Image: John Weinstein/Field Museum

Formed climate zones

But when the 150km-wide asteroid broke apart, it generated way more dust than usual, partially blocking sunlight from reaching Earth and causing the planet to cool.

Study author Philipp Heck, a curator at the Field Museum in Chicago and associate professor at the University of Chicago, said: “Normally, Earth gains about 40,000 tonnes of extraterrestrial material every year. Imagine multiplying that by a factor of 1,000 or 10,000.”

The researchers said the dust floated down to Earth over 2m years, leading to a gradual cooling process that divided the planet into climate zones – with colder temperatures at the poles and tropical conditions at the equator. This slow cooling action allowed for an explosion of new species that were able to adapt for survival in regions with different climate conditions.

To understand how the process occurred, the researchers said they analysed the chemical composition of 466m-year-old rocks from a fossil site in Sweden by treating them with acid and extracting space dust from them.

Shot of a cliff with different sediment layers with a small, blue truck nearby.

Cliffs made of sedimentary rock that was once an ancient seabed. The grey horizontal line in the rock shows where the dust from the asteroid collision fell. Image: Philipp Heck/Field Museum

‘This result was completely unexpected’

To prove this dust originated from space, they looked for the presence of a specific type of helium isotope that is often found in asteroids.

Birger Schmitz, professor of geology at Lund University and the leader of the study, said: “This result was completely unexpected. We have, during the last 25 years, leaned against very different hypotheses in terms of what happened. It wasn’t until we got the last helium measurements that everything fell into place.”

Over the last decade, researchers have explored the possibility of using artificial methods to cool the Earth in the event of a major climate disaster.

Computer simulations have shown that it would be possible to place asteroids – like satellites – to orbit around Earth in a way that allows them to continuously create fine dust to help block sunlight.

Schmitz said: “Our results show for the first time that such dust at times has cooled Earth dramatically. Our studies can give a more detailed, empirical based understanding of how this works, and this in turn can be used to evaluate if model simulations are realistic.”

But Heck advocates a more cautious approach to these methods, saying: “Geoengineering proposals should be evaluated very critically and very carefully, because if something goes wrong, things could become worse than before.”

– PA Media