It probably says something pretty deep about my warped mind, but I find myself fascinated by the phenomena known as mass-extinctions. Mass extinctions are killing events that have removed significant numbers of species from the tally of the Earth’s life. Probably one of the major reasons I am interested in these awful processes, is that we are in the midst of one, and unlike almost all others, humanity is the cause of this one. And the truly horrible thing about that is, that we know it is occurring, and that our species in aggregate shows its immaturity by actively refusing to do anything about it. Ah, well, at my age, my own personal extinction is not all that far off, and there is little I can do about most larger issues anyway, so…
Mass extinctions are a fact of life on Earth, but strangely enough they have only intensively been studied within the last 25 to 30 years. Back in the bad old days when I was in grad school, the greatest extinction event ever, the end-Permian extinction event, was not even recognized by many paleontologists, let alone neontologists, and although some mass extinctions were known because the faunal changes that resulted from them were used to determine geological time periods, nobody studied those mass extinctions themselves. This all changed in the amazing kerfluffle of research following the Alvarez et al., 1980, paper proposing that the Cretaceous-Tertiary, or End-Cretaceous, mass extinction exposition, wherein the (larger) dinosaurs perished, was caused by an asteroid impact.
The explosion of fuss and feathers this paper caused, I think, had to be lived through to be believed. Helen of Troy, the legendary face that launched a thousand ships, and the Alvarez et al. 1980 article launched at least a thousand research projects, and maybe ten times that many follow-up articles. The upshot, of course, is we now know Alvarez, et al. were right; an impact with a large asteroid certainly hastened the large dinosaurs out the door, if it didn’t kill them all by itself. And the discovery of the smoking gun, er… watery crater, the Chicxulub crater off the northern Yucatan Peninsula, lead to an awareness that the Earth was in a perpetual celestial game of dodge ball, and even though most of the really big rocks appear to have hit the planet long ago, every now and then…
And, of course, that means the Earth WILL get hit again, and actually it is getting hit all the time, except the bombards are small much smaller.
All of this has resonated with me, because I have been a fan of meteors – as small asteroids that burn up in the atmosphere are called – ever since I used to lay out our backyard at night as a kid and see the occasional “shooting star.” I entertained the hope that one day I would be in the right (?) point at the right time, and see a really big meteor. I have remained hopeful of that eventuality, but am more mindful now that I might not want to be too close.
About two weeks ago, what has been estimated to be the largest object to hit the earth since the Tunguska object of 1908, arced over Russia, exploding more-or-less over Chelyabinsk, Russia, spraying small fragments that impacted on the ground west of the city. From the sequence of things that happened during the event, the object has been since estimated to have been a small asteroid weighing about 10,000 tons and about 15m to 20m in diameter, travelling at about 18 km/sec (40,000 mph).
Apparently research that also ultimately resulted from Alvarez et al., 1980, showed that most stony asteroids of that size tend break up and explode rather than hit the earth. And explode this one did, at an altitude of 15 to 20 km (9 to 16 miles) with an explosion that was considerably brighter than the sun. Equipment in place to detect atmospheric nuclear tests nicely detected this explosion, and its size was estimated to be in the range of a blast by a thermonuclear device with a yield of about 500 kilotons, the size of a decent ICBM warhead. Even though the explosion was at a high altitude, over 1000 people were injured and there was extensive damage due to shock waves.
Some closing thoughts, I don’t know if the rock could have held together to explode with that force nearer the ground, but if it did, the damage could have been much greater. Several people have discussed what might have happened if the position of the earth or the rock were varied by a minute or less in the relative orbits – it could have entered the atmosphere at a much steeper angle and perhaps over a larger city or populated area. Or perhaps the best/worst thought: Chelyabinsk was a city where a lot of weapons research was done during the cold war. What would have been the outcome of this rock hitting near there in, say, 1978?
I grew up in Great Falls, Montana, home of Malmstrom Air Force Base, around which in 1962 the first 150 Minuteman Ballistic Missiles were emplaced in “silos”. Judging from the palpable tension at times in that community during “Duck and Cover” days, if an asteroid had appeared out of nowhere on a low ballistic trajectory (as this one was described by the Russian military) and exploded 10 miles above that city, I suspect there would have been trails of launching missiles visible from those missile silos for a 100 miles around the town. I dare say, the same outcome would have occurred on the Soviet side. The ultimate result could have been rather severely unpleasant.
Some closing thoughts; rocks of this size are now estimated to hit the Earth every century or so, an estimate that dovetails nicely if one considers the last known impact was the Tunguska in 1908. However, at least though most of the 20th century, large areas of the Earth, such as much of the Indo-Pacific and Antarctica, could have experienced such a meteor impact and nobody would have been the wiser. Additionally, for example there was the Grand Teton fireball of 1972, which was essentially the same size as this latest impact, but which simply grazed the atmosphere. So.,. Such impacts could be more frequently enjoyed events. In any event, the regularity of such events is a statistical phenomenon, and the next one could happen tomorrow or 531 years from now.
I now have another blog, on the Reef2Rainforest site. There may be some overlap between that site and this one from time to time, but if so, the material will appear on that site first.
Alvarez, L. W., W. Alvarez, F. Asaro, H. V. Michel. 1980. Extraterrestrial Cause for the Cretaceous-Tertiary Extinction. Science. 208. 1095-1108.