Mass Extinctions On The Earth :: essays research papers

IntroSixty-five cardinal years ago, some phenomenon triggered mass extinguishings on the lands and in the oceans so lumbering that they define the geological boundary between the older Mesozoic Era, very such(prenominal) c in alled the "Age of Reptiles," and the modern Cenozoic Era, the "Age of Mammals."On a fine scale, the extinctions define the boundary between the Cretaceous (geological symbol, "K"), and Tertiary ("T") periods. This mass extinction is usually referred to as the K-T extinctions. The dinosaurs became extinct during the K-T mass extinction. To judge how the K-T extinctions fit into a broader perspective, please see the The cause of the K-T extinctions is one of the immense mysteries in science, and many scientists have proposed theories to account for it. Theories span a massive spectrum of causes including sea level change, supernova explosions, climate change, and on and on. Beginning in the 1980s, 2 new theories became th e topic of an intense scientific debate. They are the K-T impact extinction possibility originated by the Nobelist physicist, Luis Alvarez, and his team, and the K-T Deccan Traps extinction theory, which, for short, is called volcano-greenhouse theory.Details of the Impact TheoryIn the mid-late 1970s, Luis Alvarez and his impact team began searching for the cause of the K-T extinctions. His evidence of impact was enrichment of the chemical, iridium, in a thin layer of clay a few centimenters chummy at the K-T boundary. His original theory held that a giant asteroid struck earth 65 million years ago, blasting so much dust into the atmosphere that it blocked out sunlight, and plunged earth into the blackness and ratty of a sudden, short-duration, "impact winter."According to Alvarez theory, the global blackout triggered extinctions among the plant kingdom, and consequently among herbivores that depended upon plants for food, and then among the carnivores that ate the herb ivores. Those smaller animals that could hide and hibernate until the sun came out again must have sruvived and formed the animals that there are today. in that respect is other evidence for this theory there is a layer of iridium found on top of the fossils which can be found all over the world. this is important becouse there is a lot of iridium on asteroids while on earth it is only deep down indoors the crater.Details of the Volcano TheoryAnother less popular theory to explain the disappearance of the dinosaurs suggests that a drop in the oxygen levels in the lower atmosphere led to the gradual death of all kinds of species.