Not only geologists are waking up to the influence that stray asteroids and comets have had on geological and biological evolution, but so too are politicians. Despite the minuscule chances of a sizeable body hitting the Earth within our lifetime, the devastation would be awesome. Insurance actuaries have calculated the risk from such rare events, taking into account the number of likely deaths in the same way as for airline disasters. You or I are more likely to perish in the aftermath of an asteroid or comet strike than from botulism or a fireworks accident, and the risk is comparable with that of intercontinental flying. Governments are beginning to find money to support systematic mapping of bodies that may pose a threat; not a lot, but sufficient to spot bad news and refine the risks.
On June 22, a French-US team released a first assessment of the near-Earth objects (NEOs) that pose the biggest threat; those more than 1 kilometre in diameter (Bottke, W.F. et al., 2000. Understanding the distribution of near-Earth asteroids. Science, 288, p. 2190-2194). They estimate about 900 big asteroids in orbits that will pass eventually within a few moon distances of us. “Sometime in the future, one of these objects could conceivably run into the Earth,” warns astronomy researcher William Bottke at Cornell University. “One kilometer (about .6 of a mile) in size is thought to be a magic number, because it has been estimated that these asteroids are capable of wreaking global devastation if they hit the Earth.” Much smaller objects caused the celebrated Meteor Crater in Arizona (20 000 years ago) and the Tunguska explosion (1905), and seem to pose the greatest hazard, being undetectable at present.
The Cambridge-Conference Network (CCNet) freely provides a regular electronic newsletter about research into short-lived catastrophic events, including climate change, the effects of supervolcanoes, and impacts, both in the geological record and possible in future from NEOs. To subscribe, contact the moderator Benny J Peiser at firstname.lastname@example.org .
The K-T event is back for the death of the dinosaurs
Just when those palaeontologists who don’t like ‘whizz-bang’ theories for the fossil record had begun once more to feel comfortable, the geological record has bitten back.
One of the main planks against an impact cause for the extinction of all the dinosaurs at the end of the Cretaceous Period was the raraity of their remains in the top 3 metres of the Hell Creek Formation in the Great Plains of North America. The Hell Creek Formation is noted for clear signs of the Chixculub bolide strike very close to its top, as well as for a rich dinosaur fauna. Previous workers stated that a rarity of dinosaur signs just below this signified that they were under considerable evolutionary stress before any catastrophe; support for a gradualist notion of mass extinction. A team of geologists and biologists from the US have just published the results of a painstaking survey of the Hell Creek (15 thousand hours of field survey of 11 million square meters of its outcrops in North Dakota and Montana) (Sheehan, P.M. et al., 2000. Dinosaur abundance was not declining in a “3 m gap” at the top of the Hell Creek Formation, Montana and North Dakota. Geology, 28, p. 523-526). Their work finds that the top 3 metres are just as rich in dinosaur signs as any of the strata below it, right up to the layer immediately beneath the signal of Chixculub. They do not report any findings from above the impactite, though dinosaur teeth are reported to be present by earlier workers.
As journalists say, this will run and run!