Did faraway asteroid collision spark Earth’s cooling?

EDale Gnidovec

xtinction has been a factor on our planet since life first appeared. Over 99.99 percent (actually, with many additional 99s) of all the species that have ever lived are now extinct.

Many of those extinctions happened during what scientists call mass extinctions — times when large numbers of species have become extinct during relatively short intervals. The K/ Pg (formerly K/T) extinction 66 million years ago, the one that wiped out the non-avian dinosaurs, gets most of the press, but there have been at least four others.

There have also been times when the number of species has increased dramatically over short intervals. Such events usually followed mass extinctions, when there was plenty of unoccupied “ecological territory” to be filled.

One such episode that didn’t follow a mass extinction is called the Great Ordovician Biodiversification Event, or GOBE, around 465 million years ago during the

Ordovician Period. Over a period of just a few million years, the number of species tripled.

One suggested cause is gradual global cooling. Although rapid cooling has caused extinctions in the past, gradual cooling may have triggered the GOBE.

But what on Earth caused the cooling? Perhaps it wasn’t something on Earth. Maybe it was something in space.

A limestone quarry in Sweden produces slabs for window sills, table tops and floor tiles. In a narrow band of that quarry, 130 “fossil” meteorites have been found, meteorites that fell into the shallow sea that covered Sweden during the Ordovician Period. Of those, 129 are pieces of an asteroid that was shattered by a collision with another asteroid.

That collision happened 466 million years ago, and over the next two million years the number of meteorites falling to Earth increased dramatically, as shown not only by the multiple meteorites found in the quarry but also by an increase in the amount of meteorite dust present. Extraterrestrial dust is always falling, but at that time the amount of dust falling on Earth increased by 1,000 to 10,000 times today’s rate.

A new report suggests that so much dust falling through the atmosphere interfered with the amount of sunlight hitting Earth, causing the gradual cooling that may have led to the GOBE.

The asteroid collision that produced the increase in meteorites and dust occurred between the orbits of Mars and Jupiter. That something happening so far away can have such dramatic effects on Earth just shows, once again, how everything is connected.

Dale Gnidovec is curator of the Orton Geological Museum at Ohio State University. gnidovec.1@osu.edu