The fossil records tell us that there have been severalmassive extinction events in the life of the Earth. We nowknow the reasons for some of them?for instance, thedinosaurs were wiped out by an asteroid that broke intopieces upon impact, producing dust which blocked the lightof the sun. Recently, a consistent 62 million yearextinction cycle has been discovered. The last greatextinction took place 65 million years ago, and the cyclemay still be in place, because earth's biodiversity hasbeen in decline for about 2.8million years, ever since the Central American land bridgeappeared and altered the flow of ocean currents around theequator. This would mean that a new extinction event beganjust about exactly 62 million years after the last one.
The rising of Central America has played a role in theclimatic instabilitythat has caused numerous radical climate shifts from warmperiods to ice ages ever since, causing species to decline.Human beings, because of our intelligence, have been able toadapt to these extreme changes of climate, and thus we havethrived while hundreds of thousands of other species havegone extinct. But now human activity has increased the speedof extinction toabout what it was at the climax of the dinosaur extinction.
Does this mean that man is about to go extinct? Somescientists fear so, but it's far more likely that ourintelligence will take us across this latest extinctionevent successfully, and we will still be here when theplanet's climate becomes stable again--although perhapschastened by the experience of the power of nature that isbeginning to unfold around us now.
The greatest mass extinction ever recorded occurred 250million years ago, between the Permian and Triassic periods,during which time 95% of life on Earth died off, didn?toccur as a result of a single event. According to Naturemagazine, Chinese fossils show that it happened in at leasttwo phases. Maybe for this to happen, all the wrong thingshave to happen in a certain sequence.
Some scientists think the extinction event was started bythe impact of a space rock of the kind that wiped out thedinosaurs much later, around 65 million years ago.Additional factors could have been excessive volcanism,sending plumes of smoke and ash into the air, and globalwarming, which may have released methane from the sea floor.
Now scientists have found a new clue to the mystery:cyanobacteria. These one-celled organisms filled the oceansduring the Permian period and were the basis of the marinefood chain. Like plankton today, they used photosynthesis togather energy from the sun, and were a major food source forhigher marine creatures. Their fossils can be found in rocksthat date from the end of the Permian period in places likeChina, Italy and Pakistan. Phytoplankton that wasn't eatenby higher organisms would have fallen to the seafloor overtime and become incorporated into these sedimentary rocks.
By examining these fossilized rocks, researchers can seethat the number of Phytoplankton peaked at two periods, attimes when the die off of higher marine animals allowed themto flourish. So while we don't know exactly why so many fishand higher marine creatures died off, we do know when ithappened, meaning we may be able to track it back tospecific events. And the Permian-Triassic mass extinctiondidn?t just affect life in the oceans?it killed off about95% of all land animals as well.
What set the whole cycle off and why should we care? Sincewe?re in the midst of a major extinction cycle right now, itmight help us to stave it off if we can figure out what wentwrong in the distant past. There may come a point when theprocess takes on a life of its own, and it becomes too lateto reverse it through ecological intervention.
Art credit: http://www.freeimages.co.uk
Sometimes science isn't just a process of research?it alsohas to do withintuition.Subscribers canstill listen to Anne Strieber?s fascinating interview ofSonia Choquette, as well as download it to an MP3 disc andlisten in the car.
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