When I was younger, I wanted to be a geologist. Until I figured out that would most probably mean working for an oil company. I have nothing in particular against the oil industry (except the things we all have against the oil industry), but it didn't sound like a lot of fun. In any case, I've kept up with the geological literature over the years, mostly by studying up in the wonderful New Scientist magazine, various reading, and via long conversations with a neighbor who's in the field.
I did really well as an undergraduate Geology major. In fact, one of the only lousy grades I even got was for a paper I did reviewing the various theories on the causes of mass extinction (this was just before Alvarez & Alvarez pretty much established that the KT extinction of our dinosaur friends had been due to an asteroid impact). In addition to getting a poor grade, I discovered a principle: when people don't have a good explanation for something, they pretty much don't want to hear about it. Now the pendulum seems to have swung the other way. We now have an explanation (asteroid and comet impacts) and mass extinctions are the subject of scientific obsession.
One thing mostly overlooked in all this is that while really large impacts of the sort that wiped out the dinosaurs are extremely rare even in geological terms (every 100 million years or so), as you go down the scale and look at smaller impacts, they become much more frequent. We actually got smacked with a pretty good-sized one in 1908. It was just a wee bit of comet — estimated to be about 1,000 times as powerful as the bomb dropped on Hiroshima. If it had hit London or Paris instead of Tunguska, a remote corner of Siberia, the history of the 20th century would have been written a little differently.
One of the interesting things about the "Tunguska Event" is that until we came up with a pretty good explanation of it (a cometary fragment which exploded in mid-air), mention of it was found mostly in strange UFO-type publications — even though there was no particular reason to doubt it had happened. Again, no explanation so we don't want to hear about it!
Probably not coincidentally, the Tunguska impactor hit on June 30th, right at the height of the annual Taurid meteor shower, thought to be associated with the breakup of the comet Encke. From this insight (along with a number of others) grew the so far mostly British school of thought known as "Coherent Catastrophism," which suggests that the Earth is periodically subject to fairly massive storms of impacts as it passes through debris trails from fragmented comets. Shortly after the break-up of a comet, the debris is particularly concentrated and it's possible that for a period of some centuries, fire from the sky is a fairly common and much-feared part of life.
When I was a kid taking Geo 2, the very idea of catastrophes in geology was anathema, all dating back to an 18th century feud between those looking for biblical explanations of geology (Noah's flood, etc.) and those embracing empiricism. The "Uniformitarians" (no catastrophes, everything happens gradually) won out to the extent that spending time investigating actual catastrophes became career suicide in geology. One of the more amusing illustrations is the career of J. Harlen Bretz who in 1923 wrote the first of many papers suggesting that a huge area of eastern Washington State had been shaped by catastrophic floods. But... at first he had no explanation of where the water would have come from, and we know how that goes. Bretz was finally vindicated (the water came from giant glacial lakes behind huge ice dams which occasionally failed) but only because he lived to be 99. Someone asked him how he felt after receiving the highest award of the Geological Society of America at age 97, and he was reported to have said that his only regret was that he couldn't gloat properly because he had outlived all of his enemies.
Anyway, back to the Brits and their nutty theories. The two pioneers of coherent catastrophism are Victor Clube and Bill Napier, both distinguished astronomers (Oxford, Royal Observatory, etc.). They've written 2 books on the subject for general readers, The Cosmic Serpent (1982) and Cosmic Winter (1994). Both books look at the science of cometary debris and impacts, and also try to make connections between various events and writings in early history and possible impacts. I don't doubt that they will be proven wrong on many particulars, because that's the nature of even informed speculation, but I think they will ultimately be proven right: that impacts have been much more frequent and important in human history than previously recognized, and that at least some of those curious references to fire falling from the sky, etc. in various mythologies (including the Bible) will be proven not to be arcane metaphors but descriptions of actual events.
A third Clube & Napier book shows up in various listings for 2004, but was apparently never published. Napier has recently turned to writing scientific thrillers, no doubt a much more rewarding pursuit (I read one called "Nemesis" and it was quite all right). Unfortunately, both of the "Cosmic" books are long out of print and relatively rare (you'll pay between $65 and $200 — ouch!). However, a number of people have picked up where Clube and Napier left off, and I'll try to get an annotated list of good coherent catastrophism books up shortly. In the meantime, I think Rain of Iron and Ice by John S. Lewis is probably the best place to start.
The most interesting catastrophe theory to emerge in recent years is the notion that a comet impact may have wiped out much animal life (and likely most human life) in North America approximately 12,900 years ago. The comet gets its nickname from the fact that the highly developed and geographically widespread Clovis culture apparently vanished at the time of impact. This BBC article from May, 2001 was one of the earliest popular news stories on the subject: did a cometary impact kill the large mammals of North America?
Since that story was published, a great deal more evidence has been gathered and the story seems to be in the process of going from “fringe science” to mainstream, although the general public is still not much aware of it. I can recommend two excellent sources. The first is this peer-reviewed scientific paper published in the Proceeding of the National Academy of Sciences. The second is “The Cycle of Cosmic Catastrophes” a more informal account (two of the three authors contributed to the PNAS paper). You will have to trust me when I say that you should take neither the silly title or the incredibly goofy cover design seriously -- this is very real science.
The Clovis comet was quite recent -- traces of it are still found all around us in North America, including an odd black layer of sediment that's found in locations as far apart as New Mexico and Alberta. I really enjoyed a friend's terse and horrific description of what the sedimentary record tells us about life after the Clovis impact:
A big pile of bones sprinkled with radioactive dust and then a layer of algae eating up the remains. The occasional stone tool from starving people digging up the corpses for meat.
Sounds like the time my wife served Margaritas in beer steins.
Ironically in terms of the history of science, Noah's flood and the legend of Atlantis may actually turn out of be a distant memory of massive rains and flooding triggered by the debris from the Clovis comet. So while wrong about little details like the Earth only being 4,000 years old (!), the 18th century catastrophists may have been right about the reality of Noah's flood (which is but one example of many hundreds of similar flood mythologies from around the world).
A more interesting lesson is that over the last 50 or 60 years, numerous “crackpots” (and most of them no doubt were a bit cracked) came up with all sorts of odd theories focused especially on the sudden death of the mammoths. I remember reading back in the 1970s about mammoths more or less flash-frozen with their last bite of grass still in their mouths and thinking “That's odd! What in the world could kill and then suddenly freeze something as large as a mammoth?” And yup, crackpot theories or no, it was odd. So much as they can annoy us at times, we should raise our glass to the crackpots among us for helping to keep interest in this particular mystery alive.
This is a little dry (it's an actual for real scientific conference panel discussion) but full of great info:
It's a youtube clip from a panel discussion at the Pecos Archeological Conference Saturday, August 9, 8:00 am to 10:00 am. The title of the discussion was "Comet Theory, End of Clovis and the Black Mat." The chair of the panel was Dr. Christian E. Downum, Northern Arizona University. Guests were: Mark Boslough, Sandia National Laboratories, Carolyn Shoemaker, Co-Discoverer of Comet Shoemaker-Levy 9, John McCone, Planetary Geologist Arizona State, Allen West, GeoSciences Corporation, and Ted Bunch, former chief Exobiology, NASA.
The panel discusesses the context of the Clovis Comet impact in Southwestern archeology and C. Vance Haynes paper in PNAS concerning the Black Mat termination boundary.
The link is to part 1, which lasts about 10 minutes but youtube's navigation will find the other parts for you.
I watched the program (it's available for sale via the above link in June, 2009) and thought it was quite good. In only an hour, there was some ground they couldn't cover (e.g. the “peppered tusks” evidence). It did a great job of covering the passion of scientific argument and discovery, had some great visuals, and did a nice job of presenting the basic theory. I watched it with some professional geologist friends and they were initially skeptical, but quite impressed by the nano-diamond evidence.
And boy, if Bobby Jindahl discovers that people are spending so much time, money, and energy and using so much fancy equipment researching what killed the Mammoths, is he ever going to be mad!
I'll put some links up here from time to time, often to BBC stories, since their links should last until the next catastrophe.
Right in keeping with Clube & Napier's idea of coherent catastrophism...
More evidence that an impact may have been involved in the extinctions of the Wooly Mammoth and other large Ice Age critters of North America.
yet another BBC story (reporting on a peer-reviewed paper in Science) strengthening the Clovis comet theory.
And here's another fun catastrophe: Megaflood 'made Island Britain' ("Britain became separated from mainland Europe after a catastrophic flood some time before 200,000 years ago, a sonar study of the English Channel confirms. The images reveal deep scars on the Channel bed that must have been cut by a sudden, massive discharge of water.")
A future catastrophe -- the collapse of Cumbre Vieja, a volcano in the Canary Islands will likely produce a huge tsunami devastating much of the U.S. East coast: http://www.es.ucsc.edu/~ward/papers/La_Palma_grl.pdf. By the time the waves get to Florida, they will be “only” 20 to 25 meters high (about 60 to 80 feet).
Interesting poster session paper on the possibility that a impact-related tsunami took place in the NYC area 2,300 years ago: http://www.lpi.usra.edu/meetings/lpsc2009/pdf/2276.pdf. The lead author is a college undergraduate - nice job!