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fandomhigh2006-01-23 07:05 pm
dr-tommy.livejournal.com) wrote in fandomhigh2006-01-23 07:05 pm
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Paleontology, Jan 23rd (7th period)
"So, so far we’ve talked about what fossils are, how they’re made, and the geologic time scale. This week is gonna be last one before we start moving on to stuff that’s a little more, well, hands on. Today, we’re going to talk about mass extinctions. An extinction event- sometimes called an Extinction Level Event, or ELE for short- occurs when a large number of species die out in a relatively short period of time." Tommy then proceeds to give a not very exciting lecture:
"The "Big Five" mass extinctions are ones that are widely agreed upon as some of the most significant: End Ordovician (444 million years ago), Late Devonian (360 million years ago), End Permian (251 million years ago), End Triassic (200 million years ago), and End Cretaceous (65 million years ago).
So, what caused these mass extinctions? Well, that’s a good question. And the answer is- nobody really knows. Scientists have, however, come up with several hypotheses:
Impact events - The impact of a large asteroid or comet could create Megatsunamis, global forest fires, and simulate nuclear winter from the dust it puts in the atmosphere. Taken together, these and other related effects might be enough to disrupt the global ecosystem and cause extinctions. The End Cretaceous is the only extinction event to have strong evidence that points to such an occurance. Circumstantial evidence, however, is also given for the End Permian, End Ordovician, and End Jurassic ELEs.
Climate change - Rapid transitions in climate may be capable of stressing the environment to the point of extinction. However, it is worth observing the recent cycles of ice ages are only believed to have had very mild impacts on biodiversity. Extinctions suggested to have this cause include: End Ordovician, End Permian, Late Devonian, and others.
Volcanism - The outflow of millions of cubic kilometers of lava in a short duration could possibly poison the atmosphere and oceans in a way that may cause extinctions. This cause has been proposed for the End Cretaceous, End Permian, End Triassic, and End Jurassic extinctions.
Gamma ray burst - A nearby gamma ray burst (less than 6000 light years distance) could sufficiently irradiate the surface of the Earth to kill organisms living there and destroy the ozone layer in the process. From statistical arguments, approximately 1 gamma ray burst would be expected to occur in close proximity to Earth in the last 540 million years. This has been suggested as an explanation for the End Ordovician extinction event.
Plate tectonics - It has been suggested that the opening and closing of seaways and land bridges may play a role in extinction events as previously isolated populations are brought into contact and new dynamics are established in the ecosystem. This is most frequently discussed in relation to the End Permian mass extinction.
Today's discussion question is this: In the last fifty years, the rate of extinction has risen dramatically. Are we in the middle of another extinction event? If so, what do you think caused it?"
After the discussion, Tommy collects the homework and calls for presentation volunteers once again.
"The "Big Five" mass extinctions are ones that are widely agreed upon as some of the most significant: End Ordovician (444 million years ago), Late Devonian (360 million years ago), End Permian (251 million years ago), End Triassic (200 million years ago), and End Cretaceous (65 million years ago).
So, what caused these mass extinctions? Well, that’s a good question. And the answer is- nobody really knows. Scientists have, however, come up with several hypotheses:
Impact events - The impact of a large asteroid or comet could create Megatsunamis, global forest fires, and simulate nuclear winter from the dust it puts in the atmosphere. Taken together, these and other related effects might be enough to disrupt the global ecosystem and cause extinctions. The End Cretaceous is the only extinction event to have strong evidence that points to such an occurance. Circumstantial evidence, however, is also given for the End Permian, End Ordovician, and End Jurassic ELEs.
Climate change - Rapid transitions in climate may be capable of stressing the environment to the point of extinction. However, it is worth observing the recent cycles of ice ages are only believed to have had very mild impacts on biodiversity. Extinctions suggested to have this cause include: End Ordovician, End Permian, Late Devonian, and others.
Volcanism - The outflow of millions of cubic kilometers of lava in a short duration could possibly poison the atmosphere and oceans in a way that may cause extinctions. This cause has been proposed for the End Cretaceous, End Permian, End Triassic, and End Jurassic extinctions.
Gamma ray burst - A nearby gamma ray burst (less than 6000 light years distance) could sufficiently irradiate the surface of the Earth to kill organisms living there and destroy the ozone layer in the process. From statistical arguments, approximately 1 gamma ray burst would be expected to occur in close proximity to Earth in the last 540 million years. This has been suggested as an explanation for the End Ordovician extinction event.
Plate tectonics - It has been suggested that the opening and closing of seaways and land bridges may play a role in extinction events as previously isolated populations are brought into contact and new dynamics are established in the ecosystem. This is most frequently discussed in relation to the End Permian mass extinction.
Today's discussion question is this: In the last fifty years, the rate of extinction has risen dramatically. Are we in the middle of another extinction event? If so, what do you think caused it?"
After the discussion, Tommy collects the homework and calls for presentation volunteers once again.