End of the World Pt 3: Asteroids
by Cath Murphy
March 14, 2012
For reasons best known to the race of space creatures who pick which films to greenlight, 1998 was the year a meteor was supposed to hit the Earth and destroy all life upon it. In the end, Tea Leonie and Bruce Willis both made noble sacrifices in Deep Impact and Armageddon but the only real damage caused by these films was to artistic integrity and, judging by his pained expression, Robert Duvall's sense of self worth.
Since then, it's all gone quiet on the subject of asteroids, at least in a cultural sense. We absorbed the impact of the message — according to Hollywood should a big one come along, it's adios amigos to anything larger than an earwig — no point digging yourself a hole, or heading for higher ground. We're talking mass extinction here and the reduction of civilization to a collection of archeological finds a billion years from now, when the octopuses have evolved lungs and the necessary grip to wield a shovel.
Or are we? Putting movie wisdom aside for a moment, what could we expect if said collision did occur?
Recent history provides us with at least the beginnings of a clue. At the end of June 1908, an enormous explosion ripped through the pine and spruce forests of Tunguska in Siberia. An estimated 80 million trees were felled and the blast was so huge, it registered on seismographs throughout Europe (my grandmother, at that time a five year old in Kiev, might well have felt the tremors). That meteoroid (opinion is split on whether it was a comet or an asteroid) was on the large side — estimated at over 50 metres in diameter — and caused its damage by exploding in the atmosphere rather than hitting the ground. But you'll notice that - since I'm writing this - the Tunguska incident, while awe-inspiring, didn't actually end all life as we know it.
Which leaves a question about why Hollywood got obsessed with the idea of an impact event as suitable fodder for Big Apocalyptic Movies. A big bang in Russia is interesting (and has spawned the usual zillion alternative explanations, ranging from an early nuclear test gone wrong to that old stand-by, alien invasion) but it's not nearly huge enough to tempt Bruce Willis in front of a camera.
The answer lies much further back in time. 65 million years further back.
Way back then a meteorite also hit the Earth, this time in the region of the Yucatan peninsula. Leaving a crater 110 miles in diameter, this bolide was about 6 miles across (so actually really was the size of a small city) and may actually have been the largest in a series of meteorite strikes on earth originating from the Baptistina or Flora families of asteroids.
It was one of the largest, if not the largest impact event to affect life on Earth and - here's the part that got Hollywood interested - scientists now agree that this event, though in itself not large enough to cause mass slaughter, went on to cause a deadly chain reaction. Even though the bolide landed in the ocean, it was vast enough to cause an aerosol effect from the impact on the sea bed. The sulfur dioxide released caused rapid cooling of the atmosphere (through the effect of dust particles) and acid rain. The loss of plant life and the small creatures forming the bottom of the food chain, led eventually to the extinction of larger species. Including the non-avian dinosaurs.
Yes, the reason we're not running around in an Earth-sized version of Jurassic Park, is because of an impact event. If it happened once, reasoned the movie moguls, chewing on their cigars, it could happen again. And thus, movie history was made...
But could it happen again? The answer is yes, statistically speaking it could. However, statistically speaking, a live hippopotamus could land on my head. How likely is it to happen? is probably the more salient question to ask.
Not very likely. Estimates on when we can expect a collision like the one which terminated the dinosaurs, vary from once every 10 million years to once every 100 million years. Smaller ones, like the bolide which exploded over Tunguska might come along every thousand years or so. But if the Big One which killed the dinosaurs happened 65 million years ago, doesn't that mean we're overdue another one? Again, no. Impact events, while not strictly random, are influenced by so many factors that we can treat them as random . And as most of us know, the probability of a random event occurring is fixed. You can toss a coin a million times and get heads a million times, but the probability of getting tails next time remains the same. That big asteroid strike doesn't become more likely with time. Thankfully.
And even if it did, there are two more things to consider. First, we're a lot better at spotting asteroids than the dinosaurs were (or even than we were back in 1908). The skies at the moment are relatively clear. NASA even provides a helpful table with a list of all the rocks out there which might decide Earth looks like a nice spot to end it all. The blue entries on this table are all under 50 metres in diameter, the larger ones well under a kilometer in size, none of them in any case likely to hit us soon, or even likely to hit us at all. If one of those 10 kilometer bad boys did happen to approach, we would register its presence long before it arrived and be in a position to send off a futuristic version of Bruce to Save Us All.
The second thing to remember: I'm writing this. We had a big one 65 million years ago. It caused a mass extinction, but it didn't cause a total extinction. Mammals, warmblooded, perhaps less specialized than the dinosaurs, made it. I'm thinking the chances are, we would make it again.
by Cath Murphy
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