Milky Way's Spiral Arms Could Not Have Caused Climate Change 86
KentuckyFC writes "One of the puzzles of Earth's climate history is an apparent 140-million-year cycle in the climate record. Various astronomers think this can be explained by the passage of the Sun through the spiral arms of the Milky Way, which also seems to have had a period of about 140 million years. The thinking is that in regions of denser star populations, supernovas would have been more common, bathing the Earth in cosmic rays more often. These cosmic rays would then have seeded the formation of clouds that cool the planet. But in recent years, astronomers have mapped out the structure of the galaxy in much more detail. And now a pair of US astronomers have reanalyzed this climate change idea in light of the new evidence. Their conclusion is that the climate change cycle cannot possibly have coincided with the movement of the Sun through the spiral arms. So whatever caused the 140-million-year climate change cycle on Earth, it wasn't the Sun's passage through the galaxy."
Re:Heh (Score:3, Interesting)
Unfortunately, Miss Daisy will still cite it as one of the many reasons she shouldn't have to keep her damn cat inside.
Re:Since these comments are going to suck.... (Score:1, Interesting)
Again, FINITE RESOURCE.
Coal isn't renewable. That's kind of the point. We will just be down the same path and the same ultimate consequences at a more accelerated rate. You are thiinking on the span of what, maybe 50, 100 years? I am thinking a bit longer term.
Just invalidates Cosmic Ray cloud seeding. (Score:2, Interesting)
A lot of the invalidations of these spaced theories tend to focus on the effects of cloud formation by cosmic rays, but are they so sure that these are the only effects that space could have? Space is pretty big, and the earth is pretty complex, and I would be willing to bet that there's going to be something out there in space, besides the obvious asteroid, that screws us.
Not Arms (Score:3, Interesting)
In 1978 is was suggested that a galactic density wave, rather than passage through the arms, was responsible for the 140 My events. This wave, with a period 1/2 that of galactic rotation, eminates from the galactic core. http://www.springerlink.com/content/k1t6v868227t7403/ [springerlink.com]
The solar system doesn't just orbit the galaxy. It oscillates up and down through the galactic plane with a period of 88 +/- 5 My. This too has been suggested as being involved in extinctions, since the galactic plane is denser than the regions outside it.
I'm glad they got a better galactic map, and I'm sure it shows what they say. But the arms themselves aren't the only things hypothesized to be involved.
Re:Not Arms (Score:4, Interesting)
One of the problems with the suggestion of moving through the galactic plane being a major issue is that the Sun is currently very close to the main galactic plane at the moment. That is something that has to be explained if you want to use this concept to prove or disprove a hypothesis regarding the orbit our solar system takes through the galaxy.
What I would be curious about is the "CO2 data" that they are using, and the assumption that global temperatures have a direct correlation to this substance, not to mention the reliability of the measurement process over the scale of billions of years to calculate what levels of this gas were through more than just a couple of galactic years. Yes, I know there are attempts to measure global temperatures over time using the geologic record, but it seems to me that both the CO2 measurements as well as measurements of the orbit of the solar system have such huge margins of error that doing a statistical comparison of the two could give you virtually any kind of conclusion that you want.
I have to assume that this paper addresses these issues in some detail (I would love to read the original paper).
One other thing that struck me, in looking at the supposed solar system orbit that they plotted in this paper, is if they have accounted for the fact that the galaxy is a dynamic and not a static place? They calculated the path of the Sun over apparently three galactic years, but at the same time all of the objects that they used for measuring protuberance of the orbit are also moving in their own galactic orbits. If there is a model that they were able to develop that shows the galactic evolution of the Milky Way over the past 500 million years. Seriously, I had no idea that stellar parallax measurements (to accurately plot the positions of stars) were so accurate and have been for long enough to not only get a good fix on the position of a large number of stars in the Milky Way to be able to also plot the apparent trajectories of this many stars and galactic nebulae. That is some trick, and such a model would have a great many other uses besides trying to prove anthropogenic global warming (or disproving an alternative hypothesis).
My understanding was that stellar parallax measurements were only good to about 1 or 2 significant digits and getting the order of magnitude down. That may have improved with the Hubble and some other star surveys with really accurate telescopes, but I don't think it is too much better than that.
Re:It is difficult to say who is right (Score:2, Interesting)