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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."
What an incoherent rant. Perhaps you should lay off the vino before posting to slashdot.
Take a look at wikipedia's graph of extinctions from the article about the history of life. I haven't done any actual signal analysis on this data.
I would buy that there is a bit more energy in the per 62 million years signal, but I wouldn't call it clockwork-like regularity. If they came up with a p-value of 0.01, I'd say that there must be something happening, but I would expect a little more consistency out of a big cosmic event like the one they're describing.
There's not really enough time to evolve another species to our level from scratch.
Well, perhaps not from scratch, but even the most massive of mass extinctions wouldn't destroy all life. There'd be plenty of bacteria, amoebas, and various other "simple" organisms around. Given that the majority of evolutionary time was spent developing these basic organisms, life would start out with a rather large head start as compared with starting from nothing.
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.
Well, not necessarily. Fossil fuels aren't completely nonrenewable - they're just nonrenewable on any sort of human timescale. 60 million years is about the age of the coal and oil we're burning now. If there was a 95% extinction today, then the next sentient species would start out at with about the same amount of fossil fuel reserves that we had.
We all know what to do, but we don't know how to get re-elected once we have done it
How about calling them hypotheses?
Let's reserve "theory" for something that actually has solid evidence.
That would go over well in a scientific forum. OTOH, in the mass media and the general population, "theory" is used the same way that scientists use "hypothesis", for a guess that's consistent with known data but hasn't been tested.
So the question is: Is slashdot a scientific or a general-reader forum? The best answer is "both". There are lots of techie geeks here; there are lots of non-techie readers with an interest in tech stuff. So we get what you'd expect: Different people use the terminology differently, and most of them can't be bothered to make their definitions clear.
I get as annoyed as others here at the frequent blatant disregard for the proper scientific terminology. But I remind myself that this isn't really a scientific forum; it's a general-reader forum with an emphasis on techological issues. So getting our terminological act together here is probably hopeless. A large fraction of the readers don't understand such issues. And a small fraction are actively opposed to correct terminology. All this is quite normal for a mixed-level forum such as this. And we need such forums to get better information out to the public than the mass media can provide.
Still, it probably doesn't hurt to occasionally point out the technical definition of a term, for the benefit of non-tech readers who are amenable to such details. In this case, we could just point out that in scientific circles, "theory" refers to a hypothesis that has been fairly thoroughly tested, has passed the tests, and is generally accepted as the best explanation we have at present. Something that explains all known data but hasn't been tested much isn't a "theory"; it's a "hypothesis".
We have good theories of cloud formation in low-level weather phenomena. For clouds at higher altitudes (>10 or 20 km), we mostly have hypotheses. People have done a lot of mathematical modelling, which is interesting but doesn't qualify as scientific testing, so the results aren't proper (scientific) theories yet. But to the mass media, they are theories, since the media is using a different dictionary.
Those who do study history are doomed to stand helplessly by while everyone else repeats it.
Your grade school called - they've revoked your graduation certificate. The arms don't rotate around the galactic center. We don't move with the arms. We're also not currently in one of the arms. So you're batting a thousand there - got everything in your statement completely wrong.
All the stars in the galaxy orbit the center. The arms are merely a density wave in the disc. As stars enter the wave, they slow down and "bunch up", forming the "arms". As they leave, they speed up and spread out. It exactly the same phenomenon as traffics jams on the freeway, and scientists use the same math when doing calculations on both.
Anywho, our solar system passes through the arms about once every 200 million years, and the last one we passed through was about 60 million years ago. Scientists don't think it's a coincidence that the last time we passed through an arm was also when the dinosaurs went extinct.