I know there are disasters just over the horizon--terrorism, climate change, the rapture--but some ends to the human race are so profoundly unavoidable that they deserve further scrutiny, even if it's just to satisfy my need for some kind of secular eschatology. Back in May, a pair of researchers led by Mikhail Medvedev* at the University of Kansas proposed a unique solution to the puzzling periodicity of mass extinctions on Earth--which happen about once every 62 million years.
According to Adrian Melott, professor of physics and astronomy at KU, the motion of the solar system exposes Earth to an onslaught of cosmic rays on a schedule that is synchronized to the mass extinctions.* credit: Mikhail Medvedev That white dot is us, oscillating through the periphery of our parent galaxy along that helpfully-illustrated snaky green path. Of doom. Like Baltimore, St. Louis or (insert economically depressed city here) writ large, the galaxy has a good side of town and a bad side. Keep this in mind the next time you're piloting a faster-than-light spaceship home after a few too many: The bad side of the Milky Way is the north side.
The KU researchers hypothesize that the leading, north side of the Milky Way generates a shock wave as the galaxy plunges through the universe. When the solar system periodically journeys up to the north boundary of the galaxy -- about once every 64 million years -- the galactic shock wave exposes Earth to a huge dose of high-energy radiation.In other words, the earth is periodically irradiated like a steaming heap of potentially contaminated ground chuck, only it ain't just the salmonella that are wiped out. The one thing that was left out of much of the original reporting on the story, the Letters section of the July 14 issue of Science News informs me, is when we're due for another trip to the wrong side of the tracks:
"We've just passed the mid-plane of the galaxy," said Melott. "We're on the way up and we'll reach a peak in about 10 or 12 million years. That's when the radiation should start getting bad again -- if our idea is right.""As for the next die-off, there is plenty of time to prepare," cheerfully notes the pr department of the University of Kansas. *UPDATE: Mikhail Medvedev, the other researcher who conducted this study, would really, really like you to know that he was co-responsible for this paper. Attention Mikhail's tenure committee: don't ignore his work on the potential extinction of the human race just because he wasn't quoted in the press release, as this harried blogger did! In fact, here's his homepage. His primary interest is theoretical astrophysics. He's also responsible for the figure used here, which, you have to admit, is pretty rad for a science paper figure, which tend to look like this. UPDATE II: Frequent commenter Chris Eldridge, who has left enough helpful information on this blog to very nearly warrant his own blog, did some extra research on this. Unfortunately our comment system is acting up (it's due to be ripped out and completely replaced in a few months, so hold tight, folks) so he had to send along his work by e-mail. Thanks Chris!
I decided to actually write Mikhail Medvedev about my concerns over this theory and he was very happy to respond in detail about this theory. I was hoping he'd post his response here. Feeling that his response was indeed important I'll try my best to post a few notes from it. From what I gathered, the cosmic radiation received at the northernmost point of our oscillation would NOT be outright deadly. He wrote that the level of CR would only be a few times higher than normal. What he seems to indicate to me is that over millions of years this is a long term stress on the biosphere which may make other events like volcanic eruptions and asteroid impacts all the more catastrophic. something that does indeed seem very logical. "There are some hints that there were episodes of increased diversification following the extinction episodes. Maybe these can be attributed to "good" mutations (thus supporting the CR hypothesis), though other explanations are equally possible." He addressed my major concern in that their paper in no way tries to show a connection with their theory and the mass die off of the dinosaurs. "This is a good hypothesis and, in fact, quite plausible. Our paper neither rules it out nor contradicts it." We cross the mid-plane twice per cycle though -- once every 31 million years so -- to me this may sort of limit how much the plane crossing actually disrupts things since the mass extinction cycle is 62 million years. I tried not to misquote or misrepresent his letter. If I have it was purely by accident but I think I got the general context about right.