Prehistoric meteor shower? |
Prehistoric meteor shower? |
Dec 13 2007, 07:02 PM
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Member Group: Members Posts: 688 Joined: 20-April 05 From: Sweden Member No.: 273 |
A real weird news story from Nature about meteor damage to pleistocene fossils:
http://www.nature.com/news/2007/071212/ful...s.2007.372.html If traces of this meteor shower has been found in both Siberia and Alaska as the story implies, then multiple impactors must have been involved. Such small meterites would lose speed quickly so the airburst must have occurred at fairly low altitude. |
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Dec 19 2007, 02:45 PM
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Member Group: Members Posts: 656 Joined: 20-April 05 From: League City, Texas Member No.: 285 |
I wonder whether this may have more to do with the mammoth using their tusks to dig in the ground (as I seem to recall that modern elephants do) and in the process embedding the metal fragments from a meteorite which just happened to be buried in the soil. In this case the "burn marks" may simply be oxidation rings and/or due to inflammation around the embedded fragments. This may also correlate with the dorsal distribution of the fragments - I would envision the mammoth pushing the tusks into the ground, then lifting. The same explanation works for the bison horns. I'm having a really tough time accepting them as due to the impact event, as any event which yields small particles moving fast enough to do this would likely also be throwing out a lot of big rocks and heat, and the bigger rocks would travel further than the small particles.
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Dec 19 2007, 03:34 PM
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Senior Member Group: Members Posts: 3516 Joined: 4-November 05 From: North Wales Member No.: 542 |
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Dec 19 2007, 04:44 PM
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Dublin Correspondent Group: Admin Posts: 1799 Joined: 28-March 05 From: Celbridge, Ireland Member No.: 220 |
Maybe not if they are fallout from a mushroom cloud. Small particles falling out of a debris\mushroom cloud will never exceed the terminal velocity for such a particle which will be too slow to penetrate flesh and bone. Some examples: Nickel Iron fragment - Density 8000kg/m^3, 1cm diameter, mass 4g, volume 0.5cc, Drag Coeff 0.7, Terminal Velocity 35m/sec (80mph) Drop that to a 1mm diameter and the terminal velocity drops to 11m/sec (25mph) Drop that to 0.1mm diameter and the terminal velocity drops to 3.5m/sec (8mph) I need a bit more time to figure out range vs initial velocity but rest assured that it happens very fast. If you take the 1mm grain and assume an initial velocity of 5km/sec the initial deceleration due to drag is just below 2000 km/sec^2. That's not going very far - frankly I'd be surprised if it went more than 50m before hitting it's terminal velocity. There is also the fact that the loss in kinetic energy needs to be bled off as heat and at higher velocities the particle will just atomize. |
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