Monday, September 24, 2007

Comet Got Da Mammoth

At the end of the Pleistocene era, wooly mammoths roamed North America along with a cast of fantastic creatures – giant sloths, saber-toothed cats, camels, lions, tapirs and the incredible teratorn, a condor with a 16-foot wingspan.

About 12,900 years ago, these megafauna disappeared from the fossil record, as did evidence of human remains. The cause of the mass extinction and the human migration is a mystery. Now a team of scientists, including Brown University planetary geologist Peter Schultz, provides evidence that an asteroid impact likely caused the sudden climate changes that killed off the mammoths and other majestic beasts of prehistory.

In the Proceedings of the National Academy of Sciences, the international team lays out its theory that the mass extinctions in North America were caused by one or more extraterrestrial objects – comets or meteorites – that exploded over the Earth or slammed into it, triggering catastrophic climate change.

The scientists believe that evidence for these extraterrestrial impacts is hidden in a dark layer of dirt sometimes called a black mat. Found in more than 50 sites around North America, this puzzling slice of geological history is a mere three centimeters deep and filled with carbon, which lends the layer its dark color. This black mat has been found in archeological digs in Canada and California, Arizona and South Carolina – even in a research site in Belgium.

The formation of this layer dates back 12,900 years and coincides with the abrupt cooling of the Younger Dryas period, sometimes called the “Big Freeze.” This coincidence intrigued the researchers, led by Richard Firestone of Lawrence Berkeley National Laboratory, who thought that the black mat might be related to the mass extinctions.

So the researchers studied black mat sediment samples from 10 archeological sites dating back to the Clovis people, the first human inhabitants of the New World. Researchers conducted geochemical analysis of the samples to determine their makeup and also ran carbon dating tests to determine the age of the samples.

Directly beneath the black mat, researchers found high concentrations of magnetic grains containing iridium, charcoal, soot, carbon spherules, glass-like carbon containing nanodiamonds and fullerenes packed with extraterrestrial helium – all of which are evidence for an extraterrestrial impact and the raging wildfires that might have followed.

Schultz, professor of geological sciences at Brown and an impact specialist, said the most provocative evidence for an extraterrestrial impact was the discovery of nanodiamonds, microscopic bits of diamond formed only from the kind of intense pressure you’d get from a comet or meteorite slamming into the Earth.

“We don’t have a smoking gun for our theory, but we sure have a lot of shell casings,” Schultz said. “Taken together, the markers found in the samples offer intriguing evidence that North America had a major impact event about 12,900 years ago.”

Schultz admits that there is little decisive evidence about the actual details about the impact and its effects. Scientists suspect that a carbon-rich asteroid or comets were the culprits. The objects would have exploded over North America or slammed into it, or both, shattering and melting ice sheets, sparking extreme wildfires, and fueling hurricane-force winds – all of which could have contributed to changes in climate that led to the cooling of the Younger Dryas period.

Those CrAZy Impactists...let's see if this stands up. Please note that the impact cannot have been that big AND David Raup's Kill Curve seems to have fallen apart multiple times. I'll wait and see. Even though this is supported by Co-Labbies - yes, we're rather strong supporters of Impact Derived Extinctions around here - I'm not buying this one as yet.


Zach said...

Anytime somebody posits a comet impact as an extinction theory, I wince. It's just become the lazy way out (not that there's not evidence for it, but you get my meaning). Let's see...a few extinction events that I know of that have been blamed on comets:
Now this one. *sigh*

Anonymous said...

Will, you list as an interest "Alternative History." This event would provide hard evidence for a number of heretofore speculative alternative human histories, including Plato's. The timing is the same. You should not dismiss this just yet.

And no, Zach, I dont get your meaning.

Will Baird said...

Unfortunately, it is of those YAGUMET[1]. Impacts have exactly one Mass Extinction that fits (KT). Vulcanism has one of those that fits (PT). The LT is tipping strongly to vulcanism but its not decided.
The rest are very undecided. The FF Boundary in the Devonian might be an impact too, but the Late Devonian as a whole is probably not due to a series of impacts.

The fact of the matter is that Impact/vulcanism have distinct signatures. They're VERY different from each other. I fscking wish that people would stop trying to shoe horn every last extinction into their model.

After I do the KT Extinction here, I am going to write a generalized what needs to be looked for in either case.

1. Yet Another Grand Unified Mass Extinction Theory.

Will Baird said...

Hola anon:

I am not dismissing this. I am just very skeptical. VERY skeptical. They have some good points for them, BUT previous attempts to connect fullerenes et al to impacts have failed.

Will Baird said...

PS this has nada related to AH, btw. This gets put under my paleo and mass extinction interest.

Anonymous said...

So which issue of PNAS is this in? I can't find it. Got a Lit Cite? Thanks

Anonymous said...

Dang, leave out eurasia,australia and south america eh?!?