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Stories and green tips related to nature, adventure, placemaking, and food systems, written by a beginning farmer/gardener and seasoned sustainability educator who loves to grow, cook, ferment, and eat local and ecologically happy food.

Saturday, February 27, 2010

Comet the cause of megafaunal extinction in North America?

Lately, my favorite thing to watch on TV has been Ken Burn's National Parks: America's Best Idea series. Sometimes I'm lucky enough to catch it when it's actually on TV, but many days I end up watching it On Demand. Last night, the only episode On Demand was one I've already seen, so I scanned through the other History & Nature shows on the Comcast On Demand menu and saw that there was something from PBS Nova called "Megabeasts' Sudden Death." I opened it to read the description and was so incredibly excited! It was an episode about the new theory of what killed off the megafauna (like mammoth, mastodon, giant sloth) at the end of the Pleistocene epoch, right around the time of the last ice age. If you recall, I wrote an entire research paper on this subject for my English class earlier this year, so I was very eager to watch the show.
Short-faced bear and other animals, with mastodons in the background.


It focused on the new evidence that a comet is what caused the mass extinction, which I did read about while researching for my paper. The episode raises some interesting questions and the theory seems like it could be a valid potential cause for the extinctions. My paper focused on human-caused extinctions, so I didn't discuss the newly proposed comet theory extensively. Basically they've found concentrations of iridium, a very rare Earth mineral that is found in extraterrestrial matter like comets, in layers of sediment dating from the time of the extinctions around 13,000 years ago. A comet hitting Earth would have created deadly conditions: fires that would burn both the animals themselves and their available food source, blackened skies, "shock waves" of wind from the impact points (think nuclear explosion). The theory is similar to the theory of what killed the dinosaurs. No crater has been found to support this theory, but some scientists believe the comet may have exploded before impact, scattering the debris and leaving no trace of the impact on the landscape. It may have hit the giant glacier that covered most of North America. The evidence would have disappeared in that scenario as well.I was wondering what would have happened to the Clovis people, who had arrived in North America around that time. It is believed by some that these immigrants from the Asian continent (arriving via the Bering Land Bridge) were the cause, or at least a major factor, in the demise of the many large species of mammal living in North America. The animals were unaccustomed to humans, unwary of them, and so these tool-wielding men killed off the animals remarkably fast, devastating the ecosystems and wreaking havoc on species' survival. They certainly hunted some of these mammals, as is evidenced by kill sites where their famous Clovis points have been found lodged in the ribs of these great beasts. Evidence has not been found to suggest that they hunted short-faced bears or saber-toothed cats, which did go extinct, so something else must have caused them to die off. But what would have happened to these Clovis people if a comet struck? I recall reading that the Clovis culture disappeared from the record, leaving no trace after that point in North America. Some attribute that to the fact that their food source was too scarce, so they migrated south and continued their reckless killing spree on the megafauna of South America (which did appear to have happened). But couldn't they also have been killed off from the same comet-caused conditions that killed of their meat source? It seems that it would fit in with the theory. Some cultures following the Clovis appear to decline rather suddenly, like the Redstone people. They may have been the ones affected by the comet, if such a comet existed. After this period, many other Paleoindian cultures emerged, eventually developing into the Native Americans of more modern times.What about the other animals living in North America who survived? Grizzly bears, moose, bison...they weren't severely affected. In the case of the overkill theory, their survival can be attributed to them being immigrants themselves and thus wary of humans or that they weren't so large as to be easily hunted. But a comet would have damaged their species regardless of these factors.

Comet theory scientists also wonder if the comet conditions caused a resultant ice age that took place during this time. Climate has been considered a possible factor in the species' extinction, but perhaps the comet is what caused this climate change. It would help explain why these animals were affected by this particular time of climate change when in previous climate change instances they were not.

At this point, many people are skeptical of the comet theory. It definitely is intriguing, but further evidence will be necessary to really bring it to the level of validity that overkill and climate change have as potential causes of the megafaunal extinctions. I'm really glad I happened to find the program last night On Demand. NOVA has some great episodes. I will definitely be searching the NOVA website for more information on interesting topics.
Giant ground sloth.


Some related articles:
- The end of an (ice) age (Oregon Daily Emerald)
- Comet theory collides with Clovis research, may explain disappearance of ancient people (University of Southern Carolina News)
- Comet theory proof found? (Canada.com)
- New Clovis-Age Comet Impact Theory (Space Daily.com)
- New Theory: Did a Prehistoric Comet 'Kill' North America? (Santa Barbara Newsroom)
- Diamonds May Offer Proof That a Comet Struck North America (Abazias.com)
- The Clovis Comet That Wasn’t? Mystery Deepens (Anthropology.net)
- The "black mat" theory (Newspaper Rock)
- End of the Big Beasts (NOVA)

Dire wolf and peccary.


Green Gal

---

"Every creature is better alive than dead, men and moose and pine trees, and he who understands it aright will rather preserve its life than destroy it."
-- Henry David Thoreau

7 comments:

  1. I've always been fascinated by stuff like this. I saw one episode of "how the earth was made" on the history channel a couple of weeks ago that talked about a huge extinction event before mammals had even evolved. Apparently all of Siberia opened up and became a giant volcano. They found ash from the eruptions as far away as South Africa and it wiped out 95% of life on earth, but also paved the way for mammals to evolve.

    P.S. I watched all those National Parks shows too, they were on PBS once a week. Thank god for DVR's. They were great.

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  2. really interesting. the clovis people however don't sound too different from modern people - come in, kill everything, destroy resources? i told a friend last night who didn't like the fact that i said the best thing for our planet would be the extinction of the human race. hmm.

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  3. Yeah. We tend to be problematic. I think today, though, if we were a much smaller species that could manage itself better and be educated about how to co-exist--because some people do have knowledge of how to, it's just a matter of educating the majority of the world about it--we would be less damaging. It's our enormous population that today is making things extra bad I think :/

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  4. And Christopher, that sounds really interesting! I'll have to look it up.

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  5. An interesting discussion. I live in the middle of a 300 million year old meteor impact zone. Even though it was a small meteor, it managed to pulverize bedrock in an area three miles across. One of my favorite books is Lucifer's Hammer by Niven & Pournelle. It's fiction, but based on the best available knowledge of the physical effects of a meteor strike. The descriptions given in the book are fascinating.

    When I was in college our Animal Behavior class reproduced a study of the effects of crowding on mouse populations. Two different populations were raised in identical 2 foot square cages. One cage began with a single pair of mice, the other with four pairs. Both cages were supplied with unlimited food and water. The population density in the second cage naturally increased more rapidly. By the time the third generation was beginning to mature, mice packed the cage and aberrant behavior was evident in every individual. The actions taken by the mice mirrored many of the criminal actions and social disorders found in human societies. In the time we had allowed to us, the first cage didn't develop a high population density and those mice led their lives in apparent normality. It was a fascinating study.

    I enjoy your posts. Keep writing.

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  6. How interesting! Thanks for sharing and thank you very much for reading my blog! :-)

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  7. I HAVE THOUGHT THAT THE MEGAFAUNA EXTINCTION WAS CAUSED BY AN IMPACT FOR AT LEAST 20 YEARS EVEN WITHOUT ANY EVIDENCE MOSTLY BECAUSE THE OVERKILL THEORY IS NOT LOGICAL TO ME. WHY? TOO DANGEROUS TO HUNT MEGAFAUNA WITH THE WEAPONS ON HAND. A WOUNDED OR DYING ONE-MAYBE. OTHERWISE THE COST BENEFIT ANALSIS WOULD HAVE BEEN TO AVOID THEM IF YOU DONT WANT TO RUN OUT OF LIVE MEN. SMALLER GAME, FISH, AND PLANTS MAKE A LOT MORE SENSE.

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I love reading comments and am always up for a discussion! Thank you!

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