Flips have happened as close together as 50,000 years, though the last one was 780,000 years ago. But, as discussed at the Greenland Space Science Symposium, held in Kangerlussuaq this week, the signs are that another flip is coming soon.
One of those signs is that the strength of the field has been falling by 5% a century recently. A similar (though more rapid) diminution accompanies the reversing of the sun's magnetic field, which happens every 11 years or so. Other evidence comes from old navigation records. Researchers such as Nils Olsen, of the Danish National Space Centre, have used such records to chart the growth of patches of abnormal magnetism. They are able to do so because these records use both compass bearings and astronomical observations to locate a vessel. The changing relationship between the two shows that patches of abnormal magnetism have been growing off south-east Africa and in the South Atlantic.
Just when the magnetic field will flip is impossible to predict from what is known at the moment; the best guess is that there are still several centuries to go. Nor is it clear how long its protective shield will be down. (The record in the rocks is little help, since a geological eyeblink represents many human lifetimes.) But understanding how the magnetosphere works now should help to deal with the consequences if and when it vanishes.
I'm wondering if all the recent exposure (Economist, USA Today, History Channel, Hollywood movies) is a good thing, because some people with money or influence might be convinced to do something, or bad because it is over-popularizing, dumbing-down and making it all sound a bit crackpot.
Tuesday, October 16, 2007
Did a comet wipe out North American mammals?
I read this New Scientist article with great interest, as I have always maintained that the most likely cause of the 10,000BC North American cataclysm was a pole shift. To me that was far more likely than "the Indians killed 22 million animals for food" theory.
New evidence shows that the cause may have been a comet:
Citing several lines of evidence, the team suggests that a wayward comet hurtled into Earth's atmosphere around 12,900 years ago, fractured into pieces and exploded in giant fireballs.
...immense wildfires scorched North America in the aftermath, killing large populations of mammals and bringing an abrupt end to the Clovis culture. "The entire continent was on fire,"
... the evidence lies in a narrow 12,900-year-old carbon-rich layer of sediment found at eight well-dated Clovis-era sites and a peppering of sediment cores across North America, as well as one site in Belgium.
In this layer the team detected several different types of extraterrestrial debris, including nanodiamonds that are only ever found on Earth in meteorites; tiny carbon spherules that form when molten droplets cool rapidly in air; and cage-like carbon molecules containing the rare isotope helium-3, far more abundant in the cosmos than on Earth.
According to one website, nanodiamonds can be found "in meteorites, protoplanetary nebulae, and interplanetary dust." Other hints that it may not necessary arrive on earth via a comet are:
"it is unclear what fraction of the nanodiamond population is actually associated with supernovae" (found here)
"An astrophysicist from Lawrence Livermore National Laboratory's Institute for Geophysics and Planetary Physics has found that some nanodiamonds, the most famous and exotic form of stardust, may instead have formed within the inner solar system." (found here)
Interestingly, the same scientists were previously promoting a supernova as the orginal cause (see my blog entry), and this is not mentioned at all in the New Scientist article! Could it be a conspiracy.....
New evidence shows that the cause may have been a comet:
Citing several lines of evidence, the team suggests that a wayward comet hurtled into Earth's atmosphere around 12,900 years ago, fractured into pieces and exploded in giant fireballs.
...immense wildfires scorched North America in the aftermath, killing large populations of mammals and bringing an abrupt end to the Clovis culture. "The entire continent was on fire,"
... the evidence lies in a narrow 12,900-year-old carbon-rich layer of sediment found at eight well-dated Clovis-era sites and a peppering of sediment cores across North America, as well as one site in Belgium.
In this layer the team detected several different types of extraterrestrial debris, including nanodiamonds that are only ever found on Earth in meteorites; tiny carbon spherules that form when molten droplets cool rapidly in air; and cage-like carbon molecules containing the rare isotope helium-3, far more abundant in the cosmos than on Earth.
According to one website, nanodiamonds can be found "in meteorites, protoplanetary nebulae, and interplanetary dust." Other hints that it may not necessary arrive on earth via a comet are:
"it is unclear what fraction of the nanodiamond population is actually associated with supernovae" (found here)
"An astrophysicist from Lawrence Livermore National Laboratory's Institute for Geophysics and Planetary Physics has found that some nanodiamonds, the most famous and exotic form of stardust, may instead have formed within the inner solar system." (found here)
Interestingly, the same scientists were previously promoting a supernova as the orginal cause (see my blog entry), and this is not mentioned at all in the New Scientist article! Could it be a conspiracy.....
Subscribe to:
Comments (Atom)