FOR MASS EXTINCTION, SIZE DOESN’T MATTER
It’s a well-known story in our planet’s past: A giant space rock slams into Earth, causing a catastrophe that ends in mass extinction. You might think the amount of devastation an impactor wreaks depends on its size. But new research suggests something else might matter more: The composition of the ground where that meteorite hits.
In work published Dec. 1, 2021, in Journal of the Geological Society, an international team of researchers examined 33 impacts over the past 600 million years. They found that whenever the rocks a meteorite struck were rich in a mineral called potassium feldspar (also referred to as K-feldspar or Kfs), the impact resulted in a mass extinction. This occurred regardless of the size of the impactor, meaning smaller meteorites striking areas rich in Kfs were more likely to cause mass extinctions than larger ones that hit regions without much Kfs.
Why might this be? Impacts throw up massive amounts of dust into the atmosphere. Called impact winter, this initially cools the planet for a year or less, but the climate quickly rights itself. The researchers propose that Kfs is the key to mass extinctions because it causes a different, longer-term effect on the climate. Kfs is a so-called ice-nucleating mineral, meaning ice tends to form around it, creating ice crystals in the atmosphere. These ice crystals make clouds more transparent and allow more sunlight through, causing Earth to warm.
Typically, a warming atmosphere melts ice crystals in clouds, reducing their transparency — blocking out sunlight and acting to balance the climate. But excess Kfs makes it harder for ice crystals in clouds to melt and can increase global warming for periods as long as 1,000 to 100,000 years. This sustained climate change has harsh consequences for life on the planet and is associated with mass extinctions.
So, when it comes to extinction-level events it appears that the mineralogy of the impact site may well matter more than the size of the impactor.