The Cretaceous Geological Periods

Cretaceous-Tertiary Extinction Event
The Cretaceous-Tertiary extinction event (also known Cretaceous Tertiairgrens, abbreviated K-Pg boundary, or KT boundary) is the transition between the Cretaceous geological periods (K) and Paleogene (Pg). In rocks, this transition can be found as a thin layer of sediment, enriched with the rare element iridium. During this transition a mass extinction took place, involving many kinds of animals and plants disappeared. This event is the Cretaceous-Tertiary mass extinction (or extinction Cretaceous-Tertiairmassa) called. Recent datings show that the boundary 65.95 million years old.

During or just before the Cretaceous-Tertiary extinction dinosaurs all disappeared (except for some birds). A small number of dinosaur fossils in layers above the Cretaceous-Tertiary extinction found, but these are explained as fossils from older strata and eroded again switched off. Besides the dinosaurs disappeared under all other pterosaurs, plesiosaurs and Mosasaurs and many species of plants and invertebrates. By the disappearance of the dinosaurs were ecological niches free, so especially among mammals adaptive radiation could take place at the beginning of the Paleogene.

The Cretaceous-Tertiary mass extinction took short compared to other mass extinctions in geological history: only a few ten thousand years. The extinction was according to most scholars, therefore, the result of a major natural disaster. There are several large impact craters found with an age of around the Cretaceous-Tertiary extinction event and was recently cut from the Cretaceous there increased volcanic activity. The amount of dust in the atmosphere increased both in the case of a meteorite as large-scale volcanism far, reducing the sunlight reaching the earth's surface. This hindered photosynthesis, so many plants and (consequently) the animals fed with them extinct. However, there are scholars who believe that the extinction took place gradually as a result of climate change or change in sea level.



Source: http://nl.wikipedia.org/wiki/Krijt-Paleogeengrens


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