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Galactic Origin For 62M-Year Extinction Cycle?
Hugh Pickens writes "Cosmologist Adrian Mellott has an article in Seed Magazine discussing his search for the mechanism behind the mass extinctions in earth's history that seem to occur with a period of about 62 million years. Scientists have identified nearly 20 mass extinctions throughout the fossil record, including the end-Permian event about 250 million years ago that killed off about 95 percent of life on Earth. Mellott notes that as our solar system orbits the Milky Way's center, it oscillates through the galactic plane with a period of around 65 million years. 'The space between galaxies is not empty. It's actually full of rarefied hot gas,' says Mellott. 'As our galaxy falls into the Local Supercluster, it should disturb this gas and create a shock wave, like the bow shock of a jet plane,' generating cascades of high-energy subatomic particles and radiation called 'cosmic rays.' These effects could cause enhanced cloud formation and depletion of the ozone layer, killing off many small organisms at the base of the food chain and potentially leading to a population crash. So where is the earth now in the 62-million year extinction cycle? '[W]e are on the downside of biodiversity, a few million years from hitting bottom,' writes Mellott."
theory about 20 years ago. However that one suggested the reason for the mass extinctions was because the stars in the galactic plane are much closer together so the likely hood of being in close proximity to a supernova and all the incumbent radiation that entails is much higher. This also explains why occasionally mass extinction skips a beat. Of course the 2 scientists who postulated this theory were promptly laughed at and ridiculed by the scientific community in that very grown up way that scientists do.
Cold fusion anyone?
Build a Man a Fire, and He'll Be Warm for a Day. Set a Man on Fire, and He'll Be Warm for the Rest of His Life.
Niven & Pournelle's "Lucifer's Hammer" started out with a nice description of this happening.
There is a war going on for your mind.
This should help our understanding.
Chime in here with any information on this.
I was lead to believe at one point that the Mayan Calendar's "Beginning of time/End of time", December 21 2012, corresponded to when our Solar System transverses the plane of the Milkway.
Where these people a few million years off? (Amongst other things)
Eric Baird
So the next thing would be an area of knowledge which deals with precisely this. Not philosophically, but more in terms of optimizing knowledge acquisition and management - or something like that. Or, speaking of reinventing the wheel, perhaps there already is?
The sun at this point is well over halfway through its yellow-phase lifetime. Earth only has a few billion more years left to reach whatever culmination it's going to. There's not really enough time to evolve another species to our level from scratch. A mere 95% extinction wouldn't be as bad, but if it's only 60-some-odd million years from now the next sentient species is going to have to make due with dramatically fewer energy reserves left on the planet to bootstrap its civilization.
In short, if you value sentience we're a pretty valuable resource for the solar system.
E pluribus unum
Hrm, I'm only glancing over the article in question, but I was just last week at a conference (North American Paleontological Conference, held in Cincinnati) where this work was presented.
As others have pointed out, cycles of diversity in the fossil record have been pointed out before, as have cycles in extinction rates. Dave Raup and Jack Sepkoski did some very important work in this. However, paleontologists have gone back and forth on whether that cyclicity really exists or not.
Melott and Bambach (Richard Bambach... a very very important paleoecologist!) presented work at NAPC that they have found the 62 mya cycle in a number of very different datasets of fossil diversity. This is important... it means the signal is very likely to be real.
I can't speak as to the astronomical mechanism they postulate; in the talk at NAPC, they suggested it might have to do with continental erosion rates (which is related to an idea Bambach has pushed many times before, particularly in a paper entitled "Seafood through Time" in the journal Paleobiology).
It will be more interesting, as Mike Foote (UChicago) pointed out at NAPC, to see if this cyclicity exists in the seperate origination and extinction rates, the combination of which produce the changes in diversity. Melott and Bambach were not at NAPC however, and the person they asked to substitute for them to present their paper (Eugenie Scott, head of an important science education taskforce) could not speak on the details of their work.