Cretaceous Extinction Event
Causes, Evidence, and Effects on Biodiversity
The most significant event of the Cretaceous era came at its end. Nearly 65 million years ago, the second most severe mass extinction in earth’s history occurred. This resulted in the loss of around 80% of species living at the time. Though nowhere near as severe as the end-Permian mass extinction, the end-Cretaceous extinction is the most well known mass extinction event. This is due to the violent event that caused it the extinction, as well as the chapter of earth’s history that it closed: the Dinosaurs. The Cretaceous Event ( often shortened to K-T event) Of the animals that were killed off were the flying reptiles (pterosaurs) and the last few mosasaurs and plesiosaurs, both early marine reptiles. Many mollusks and species of microscopic plankton were killed. Terrestrial plants suffered mass extinction as well. Almost 60% of terrestrial plants were lost. This led to high extinction rates among insect populations, especially insects that were highly specialized to feed on just a few types of plants had it the worst. It took approximately 9 million years for the global insect populations to recover from the Cretaceous extinction. Immediately after the extinction, the earth saw an explosion of short term species who respond well to fire, or other external disturbance. Evidence of the catastrophe comes from a thin rock layer deposited worldwide just after the impact. It is dominated by fossil plants whose descendants recover quickly after fires of other disturbances, such as Fire Weed in Alaska. The causes of the Cretaceous extinction are still being debated by paleontologists. Scientists agree that the main cause of the extinction was an asteroid, about 10 kilometers across, that landed in what is today the Yucatán peninsula in Mexico. The effects of the collision were catastrophic. Scientists believe that the asteroid caused a period of cold climate due to dust blocking the heat of the sun, a subsequent period of hot weather, as well as global forest fires. Regardless of what caused the extinction of the dinosaurs, the mass extinction at the end of the Cretaceous set the stage for a rapid rise to dominance of new groups of species during the following time period, the Paleocene, and then later the Cenozoic era. The species group that rose the fastest were the Paleocene Mammals, they would go on to fill many ecological niches left by the dinosaurs.
There have been many hypotheses offered about what caused the K-T extinction, however very few of them have been given serious consideration by the scientific community. The extinction poses a puzzle that paleontologists, biologists and geologists have been trying to solve for over 200 years. Scientific Hypotheses include disease, freezing cold spells, a gamma ray burst (an extremely energetic burst of x-rays released by a super-massive supernova) striking earth, heat waves resulting in populations...