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."

Comments

Clouds?

[TapeCutter]

Mabye cosmic rays effect the ozone layer, I don't really know. However claiming that CR's increase cloud cover is stretching the science well beyond what is known.

Re:Clouds?

[Burnhard]

Mabye cosmic rays effect the ozone layer, I don't really know.

A recent paper shows that this may indeed by the case

However claiming that CR's increase cloud cover is stretching the science well beyond what is known.

Given that Svensmark's team has been granted an experiment slot at CERN, at least many of those in the Physics community believe it's a plausible hypothesis. There is research out there demonstrating some causal link between cloud cover and Cosmic Rays. Science is all about reaching beyond what is known. It would be pretty a pointless exercise otherwise.

Re:Not a new idea

[Cyberax]

It's unlikely. Another star (the size of our Sun) needs to pass about 2 light-years near the Sun to significantly disturb the Oort cloud. And Sun-like starts are not that common.

However, Sun's gravitational field is so weak in the Oort cloud that even _Galactic tides_ can eject objects from it. Few years ago I helped my friend to write a computer simulation of this for his thesis.

Re:Just no

[jc42]

Is it really flamebait to say that humans are the most likely cause of biodiversity downfall?

No; it's only considered flamebait in political/religious circles. ;-)

In scientific circles, it's conventional to attribute most of the current extinction event to human activity. Thus, we don't really know when humans first arrived in the Americas, and there are estimates at high as 30,000 years ago for the first. However, it does seem fairly clear that humans were rare on those continents before about 12,000 years ago, when there was a huge increase in the human population. At the same time, large numbers of large animal species went extinct. Some of those would have died out anyway, but the mass extinction is generally attributed to humans. After all, if you introduce a new major predator, you'd expect that the sort of prey it likes (large, meaty critters in this case) would start to disappear.

So the human-caused extinction has long been the default hypothesis. There are other possibilities, but if you want to argue for them, you should have some pretty good evidence, and such evidence doesn't seem to exist. Death at the hands of a new, powerful predator is just too reasonable to be dismissed without evidence, and it quite properly the primary hypothesis when there is evidence of such a predator. And, unlike in political discussions, there is rather little scientific argument about this. Rather, there are lots of scientists looking for evidence wherever they can find it. Other contributing factors have been reported, but so far nothing much that seriously challenges the primary hypothesis.

(Actually, there is a good recent example of the opposite process. Starting about 500 years ago, there was a mass extinction of humans in the Americas. It is common to attribute this to the introduction of a different human subspecies that had better weapons. But we have the evidence, and it shows that weaponry was a minor factor in the extinction, and only in the eastern coastal areas. It turns out that most of the people in the interior died from the diseases that the new humans unknowingly brought along, long before the newcomers reached the interior. Both groups of people attributed the plagues to acts of various gods, since neither had any understanding of microorganisms at the time. It wasn't until the 1800s that "germs" were understood, and the newcomers started using biological warfare in a controlled fashion against the original inhabitants. This produced a second extinction event, but it was much smaller than the one in the 1500s.)

(And it'll be interesting to see whether this gets any "flamebait" mods. There's gotta be at least a few people who'll read it that way. I've already got both "flamebait" and "insightful" for one post; now I'm trying for "flamebait" + ("informative" || "insightful") + "funny". ;-)