Here's an interesting new theory--the large mammals of America may have been wiped out by a storm from a supernova:

Richard Firestone, a nuclear scientist at the U.S. Department of Energy's Lawrence Berkeley National Laboratory, who formulated the theory with geologist Allen West, told Discovery News that a key piece of evidence for the supernova is a set of 34,000-year-old mammoth tusks riddled with tiny craters.

The researchers believe that in the sequence of events following the supernova, first, the iron-rich grains emitted from the explosion shot into the tusks. Whatever caused the craters had to have been traveling around 6,214 miles per second, and no other natural phenomenon explains the damage, they said.

Interesting, and as the article says, it's testable. If it's true, it's a new kind of threat to worry about. I wonder if there would be any warning?

I don't think that the precision in that paragraph makes sense, though--"around 6,214 miles per second"?

That's what happens when you convert 10,000 kph and don't understand "significance digits."

(The same thing happens when you convert 37°C to °F.)

D'oh. Make that "kps", but the number's the same.

Unless it's something like this mechanism, I'm not sure I understand it. Also, 10,000 km/sec doesn't make a lot of sense even as a round number; incoming material from space rarely exceeds ~70 km/sec.

> Also, 10,000 km/sec doesn't make a lot of sense even as a round number;
> incoming material from space rarely exceeds ~70 km/sec.

Cosmic rays travel much faster than that. It's very unlikely that a supernova would emit "iron-rich grains" that would make it to Earth. The only thing that makes sense is that they're talking about iron nuclei.

Reading journalese is an art.

Jay-

Thanks for the link. I knew I had read about that somewhere (and on your blog, for that matter), and that the cosmic ray theory wasn't exactly new, but I figured I'd check the comments here before spending the time on Google. Lo and behold, there's your article! :)

Now, of course, that begs the question, if this theory was posited 3 years ago, why is it a new theory in 2005? Of course, Ed's comment about about reading journalese might explain that, too...

John - It's a new theory in 2005 because not enough people read my blog. ;^)

Seriously, thanks for the thanks. And thanks to Ed for the interpretation of journo-tongues.

Sounds like tabloid science. And the original article (a press release from Lawrence Berkeley Lab) specifically mentioned iron-rich grains. This 'cratered tusk' thing really calls everything else into question as potentially junk science. Think about it... If these things are that close together that a single tusk is "peppered" with craters, then wouldn't essentially all land-based life have been sand-blasted from almost an entire hemisphere (i.e., not just the mega-fauna)? Further, if the mean distance between these grains is that small at 250 l.y. distance, then at .25 l.y. they should be a million times closer together. Do we see the supernovae with essentially a solid wall of iron coming toward us at 10000 km/sec? And let's not even get into the whole comet-like impactors somehow condensing out and traveling 250 l.y. to impact a miniscule target like Earth. Next thing you know, somebody's going to suggest that Venus was spat out of Jupiter a few thousand years ago...

(BTW, I'm not trying to downplay the radiocarbon and other isotopic evidence. It *does* appear that something (or things) happened, but those portions of the explanation seem pretty silly on the face of it.)

- Eric.

I want to know how a grain of iron traveling at 3% of the speed of light is going to survive passage through the atmosphere. It's going to be converted to rapidly-expanding superheated plasma by impacts with air molecules long before it gets to ground level. And if it can survive passing through the equivalent of 10 meters of water, why is it stopped by a tusk?

Yes, that's what has me scratching my head, too, Paul. Unless they're postulating that the earth had no atmosphere then, and these particular megafauna were vacuum breathers.

Could it be that aliens confronted by the beast while implanting rudimentary intelligence in the minds of the primitive primates they had discovered, were forced to down the monster with a particle firing ray gun. Leaving the only real evidence of ID cryptically, but obviously deliberately left behind. Only to be discovered, ironically by those that would deliberately conceal the truth in order to thwart the truth seekers. Who’s only goal is a more rounded education for the kiddies.

An interesting theory if it turns out not to be junk, but for now I'm sticking with the theory that the settlers who came across the Bering Strait hunted them to extinction. Damned ecologically ignorant (early) Native Americans.

Isn't that about the time of the earliest cave art in Europe?

Rich

Regardless of whether this particular supernova threat is real, there are still other equally ominous supernova threats. For example, a close enough supernova could actually bathe the Earth in lethal neutrino radiation. That's a scary thought for a lot of reasons. Not the least of which is that even having the Earth between you and the supernova will not substantially reduce the neutrino flux. The good news is that such supernovae have to be really close (a handful of lightyears) and you can generally tell well ahead of time before a close supernova is going to go off, and there's nothing in the neighborhood which looks to be headed that way soon. Still, it's disconcerting to think that even an incredibly advanced future human civilization might not be able to cope with this sort of thing and survive (putting the Sun between you and the supernova ought to do the trick, getting the entire human population in the right spot at the right time would be rather challenging though).

Someone please explain how a supernova 34,000 years ago could cause mammoths to become extinct 12,000 years ago.

6,214 miles per second is 32.8 million feet/second or 100,000 km/s or about 1/3 the speed of light.

If the supernova was 22,000 light years distant wouldn't that do it?

"I want to know how a grain of iron traveling at 3% of the speed of light is going to survive passage through the atmosphere."

At 3 psol, it won't have time to be ablated.

If these tusks were in fact peppered by hypervelocity grains, it only tells us what the grains were like at the time and point of impact. It doesn't tell us whether these grains entered the atmosphere as grains, or whether they were part of an object that detonated at low altitude after screaming into the atmosphere at some speed that was just a tiny fraction of the speed of light. It may have been a localized event, like Tunguska.

Just came across this thread after so, so long, but have entertained notions of such an event for over a decade, based on qualitative evidence noted on visits to prehistoric caves in the Dordogne region of France. Some of the cave art from that 18 - 35K years BC period shows "bits" raining from the sky upon dead animals and people. Official explanations surmise battles or hunting, but the pictures don't really suggest that. Also, sleeping dugouts around the mouths of the caves are roofed by enormous stone lintels, far too massive to just keep the rain off...must have been a major project to set them into place, and a good reason to do the work. The very fact of deep cave-living in such a nice climate poses questions. Supernova debris is only one possible source of extraterrestial bombardment in this period. My guess is that some stuff--particles, grains, dust--really did rain down occasionally and make life very difficult for our remote ancestors.