When it comes to mass extinction, meteorite size doesn’t matter - Beyond The World

When it comes to mass extinction, meteorite size doesn’t matter

New research shows it’s the composition of the rock a meteorite hits, and not the impactor’s size, that causes an extinction-level event.

It’s a well-known story from the past of our planet: A massive space rock collides with Earth, resulting in a catastrophic event that results in mass extinction. You might think that the size of the incoming impactor is what matters when it comes to determining which hits will cause such widespread devastation. However, new research suggests that something else may be more important: The chemical make-up of the ground where the meteorite lands.

The study, which was published in the Journal of the Geological Society on Dec. 1, 2021, aims to explain why some meteorite impacts result in mass extinctions while others do not.  For example, the famous impact that killed the dinosaurs and left the Chicxulub crater was much smaller than many other impact events that didn’t cause massive loss of species. Why might this be?

It’s all about the dust

An international team of researchers examined 33 impacts over the past 600 million years, including experts in mineralogy, climate, asteroid composition, and paleontology. They focused on the minerals in the massive amount of dust ejected into the atmosphere by an incoming meteorite. That dust has the potential to drastically alter Earth’s climate, and scientists believe that climate change is a major cause of mass extinctions following impacts.

When a common mineral called potassium feldspar (also known as K-feldspar or Kfs) was present in high concentrations in the rocks that an incoming meteorite hit, the impact resulted in a mass extinction. This happened regardless of the size of the impactor in the 33 impacts they looked at, implying that smaller meteorites that hit high-Kfs areas are more likely to cause mass extinctions than larger meteorites that hit low-Kfs areas.

Why is this the case? It turns out that Kfs is an ice-nucleating mineral, which means that ice forms around it and forms ice crystals in the atmosphere. Clouds, which play a critical role in balancing Earth’s climate, are greatly influenced by these ice crystals. Kfs, in particular, makes clouds more transparent, allowing more sunlight to pass through and thus warming the Earth’s surface.

This has knock-on effects that could further disturb the Earth’s climate. A warming climate typically melts ice crystals in clouds, reducing their transparency and blocking sunlight, thereby balancing the climate. Excess Kfs in the atmosphere, on the other hand, makes it more difficult for ice crystals in clouds to melt, potentially accelerating global warming.

The Vredefort Dome is what remains of a meteorite impact 2 billion years ago. The original crater, which has since eroded away, had a diameter of about 190 miles (300 kilometers).
Increasing the heat

The massive amount of dust thrown up immediately after a large impact can cause cooling because it blocks out sunlight. However, the researchers claim that this effect, known as impact winter, is minor, lasting only a few months to a year. When Kfs-rich dust continues to seed ice crystals in the atmosphere over 1,000 to 100,000 years, they say, the bigger effect occurs. Finally, impacts in Kfs-rich regions of the Earth result in long-term global warming, which is linked to mass extinctions. As a result, it appears that the mineralogy of the impact site is more important than the impactor’s size.

“When we put together the data, life carried on as normal during the fourth-largest impact [in the study] with a crater diameter of [about] 48 kilometers [30 miles], whereas an impact half the size was associated with a mass extinction only 5 million years ago,” said study co-author Chris Stevenson of the University of Liverpool in the UK, in a press release.

The study “shows that it is the Kfs content of the ejecta blanket, not the size of the impact, that correlates between meteorite impacts and mass extinction events,” according to the paper. Of course, the next step is to figure out how many extinctions occur during these warming episodes and how long the effects last.

The paper ends on a profound — and perhaps ominous — note: “The available evidence suggests that, until modern times, only meteorite impacts could change the atmospheric mineralogy with such (geological) suddenness and persistence,” it reads. But now, things are different. Modern humans have the ability to drive climate change — and mass extinctions — through changes we make in our atmosphere in a way previously only achievable through giant impacts. And that puts some onus on modern society to consider the power we hold over our planet.

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