One of our newer science tropes, the dinosaur-killing asteroid, is found in school textbooks and featured on shows ranging from Nova to This American Life. Despite this being one of the few science “facts” that most Americans seem to know, according to the current Atlantic Monthly, it’s controversial among scientists. I don’t usually credit the Atlantic as a science source so I did some research, and this controversy is indeed a Thing.
No one questions that the asteroid happened–there’s a huge crater, after all. The question is whether it was large enough or even in time to create the K-T extinction. The other candidate is a truly awesome collection of rift volcanos in India known as the Deccan traps, happily inactive now.
You may have heard of Laki, an Icelandic rift volcano that erupted for eight months in 1783-84. It killed over 20% of humans and 50% of livestock on Iceland, and caused crop failures, drought, and seasonal climate extremes worldwide. That volcano released 3.3 cubic tons of material. Unhappily, it’s still quite active.
During the 300,000 years prior to the K-T extinction, the Deccan traps released 720,000 cubic tons of material. That averages to 2.4 cubic tons per year, or almost three-quarters of a Laki. The average is misleading, because the 40,000 years before the extinction were the most intense.
Either way, the Earth must have been a mess for millennia. During the Cretaceous, lava from the Deccan traps covered an area the size of modern Europe. Today, after 70 or so million years of erosion, basalt mountains over a mile high cover a region the size of France.
Those hoping humanity’s ultimate end would be a quick explosion into flame should perhaps instead contemplate centuries of choking air under gloomy skies, dying animals and plants, and poisoned water. I think this out-Mordors the Trump administration.
Reading this got me curious about our five previous mass extinctions, or perhaps I should say, the current scientific beliefs about previous mass extinctions. Here they are in millions of years ago and percent of extant species that became extinct:
- 444 mya, 60-70%
- 372 mya, >70%
- 252 mya, 90-96%
- 201 mya, 70-75%
- 66 mya, >75%
Remember, these percentages represent extinct species, not absolute numbers of animals. So if your island, where “you” are some sort of minor deity as opposed to a species on the list, contained kangaroos, koalas, sweet gum trees, monitor lizards, kookaburras, eucalyptus, dingos, sugar gliders, king-parrots, and bottlebrush, and along came an 80% extinction event, you would cross eight of those organisms off the list of life permanently. All gone.
Among the creatures that survived extinction five are gingko trees, magnolias, roaches, crocodiles, and tortoises. One scientist in the article keeps a pet tortoise as a reminder. Well, roaches are hard to train and crocodiles are hard to feed.
The fact that most species get wiped out periodically does put all environmental concerns, including climate change, into perspective. The same sort of perspective that might make one think, Everyone is going to die anyway, so I may as well kill someone.
Culminating Triad 