EXTINCTION OF THE DINOSAURS
Paleontologistshave argued for a long time that the demise of the dinosaurs was caused byclimatic alterations associated with slow changes in the positions ofcontinents and seas resulting from plate tectonics. Off and on throughout theCretaceous , large shallow seas covered extensive areas of the continents. Datafrom diverse sources, including geochemical evidence preserved in seafloorsediments, indicate that the Late Cretaceous climate was milder than todays.The days were not too hot, nor the nights too cold. The summers were not toowarm, nor the winters too frigid. The shallow seas on the continents probablybuffered the temperature of the nearby air, keeping it relatively constant.
At the end ofthe Cretaceous, the geological record shows that these seaways retreated fromthe continents back into the major ocean basins. No one knows why. Over aperiod of about 100,000 years, while the seas pulled back, climates around theworld became dramatically more extreme: warmer days, cooler nights; hottersummers, colder winters. Perhaps dinosaurs could not tolerate these extremetemperature changes and became extinct.
If true,though, why did cold-blooded animals such as snakes, lizards, turtles, andcrocodiles survive the freezing winters and torrid summers? These animals areat the mercy of the climate to maintain a livable body temperature. Its hardto understand why they would not be affected, whereas dinosaurs were left toocrippled to cope, especially if, as some scientists believe, dinosaurs werewarm-blooded. Critics also point out that the shallow seaways had retreatedfrom and advanced on the continents numerous times during the Mesozoic, so whydid the dinosaurs survive the climatic changes associated with the earlierfluctuations but not with this one? Although initially appealing, thehypothesis of a simple climatic change related to sea levels is insufficient toexplain all the data.
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