Wikipedia:Today's featured article/March 13, 2008

Artist's reconstruction of a major impact event

The Cretaceous–Tertiary extinction event was the large-scale mass extinction of animal and plant species in a geologically short period of time, approximately 65.5 million years ago (mya). It is associated with a geological signature, usually a thin band dated to that time and found in various parts of the world, known as the K–T boundary. The event marks the end of the Mesozoic Era, and the beginning of the Cenozoic Era. Non-avian dinosaur fossils are only found below the K–T boundary and became extinct immediately before or during the event. Mosasaurs, plesiosaurs, pterosaurs and many species of plants and invertebrates also became extinct. Mammalian and bird clades passed through the boundary with few extinctions, and radiation from those Maastrichtian clades occurred well past the boundary. Many scientists theorize that the K-T extinctions were caused by one or more catastrophic events such as massive asteroid impacts or increased volcanic activity. Several impact craters and massive volcanic activity in the Deccan traps have been dated to the approximate time of the extinction event. These geological events may have reduced sunlight and hindered photosynthesis, leading to a massive disruption in Earth's ecology. Other researchers believe the extinction was more gradual, resulting from slower changes in sea level or climate. (more...)

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