Starts With A Bang

Are Mass Extinctions Periodic, And Are We Due For One? (Synopsis)

A large, rapidly moving mass that strikes the Earth would be certainly capable of causing a mass extinction event. However, such a theory would require strong evidence of periodic impacts, which Earth doesn't seem to have. Image credit: Don Davis / NASA.

“That which can be asserted without evidence, can be dismissed without evidence.” -Christopher Hitchens

65 million years ago, a catastrophic impact from outer space caused the last great mass extinction on Earth, destroying 30% of the species that lived on our world at the time. These mass extinction events happened many times in Earth’s past, and the Solar System also passes through denser stellar regions of space periodically, as determined by the orbit of the Sun and stars in the Milky Way.

Every 31 million years or so, the Sun moves through the galactic plane, crossing over the region of greatest density in terms of galactic latitude. Image credit: NASA/JPL-Caltech/R. Hurt (of the main galaxy illustration), modified by Wikimedia Commons user Cmglee.

It’s a combination of facts that might make you wonder whether the extinction events are also periodic, and if so, whether periodic impacts are predictable. If so, then shouldn’t we be aware of whether we’re living in a time of increased risk, and prepare ourselves for that possibility accordingly? After all, the dinosaurs didn’t have a space program or the capability of deflecting a dangerous object like the one that wiped them out.

A measure of biodiversity, and changes in the number of genera that exist at any given time, to identify the most major extinction events in the past 500 million years. Image credit: Wikimedia Commons user Albert Mestre, with data from Rohde, R.A., and Muller, R.A.

But before we go that route, we should take a good look at what the data shows. Are mass extinctions periodic? Are we due? Let’s find out!