Cretaceous-Tertiary extinction event

The Cretaceous-Tertiary (K-T or KT) extinction event, also known as the KT boundary, was a period of massive extinction of species, about 65.5 million years ago. It corresponds to the end of the Cretaceous Period and the beginning of the Tertiary Period. (K is the traditional abbreviation for the Cretaceous period. Cretaceous comes from the Latin for chalk, creta. The K comes from the German word for chalk kreide, or possible Greek kreta. The K is used so as to avoid confusion with the Carboniferous period which uses the letter C.)

Impact event and iridium

In 1980, a team of researchers led by Nobel-prize-winning physicist Luis Alvarez, his son, geologist Walter Alvarez, and a group of colleagues discovered that fossilized sedimentary layers found all over the world at the Cretaceous-Tertiary boundary, 65.5 million years ago, contain a relatively high concentration of iridium, hundreds of times greater than normal. The end of the Cretaceous coincided with the end of the dinosaurs and was in general a period of extraordinary mass extinction, leading to the Tertiary Period of the Cenozoic Era, in which mammals came to dominate on Earth. The paper suggested that the dinosaurs had been killed off by the impact of a ten-kilometer-wide asteroid on Earth (see impact event). Two facts supporting this conclusion are that

Related Topics:
Luis Alvarez - Walter Alvarez - Concentration - Iridium - Cenozoic Era - Asteroid - Impact event

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• iridium is relatively abundant in asteroids, and
• the isotopic composition of iridium in K-T layers resembles that of asteroids more closely than that of terrestrial iridium.

Iridium is very rare on Earth's surface, but much more common in the Earth's interior as well as in extraterrestrial objects, such as asteroids and comets. Furthermore, chromium isotopic anomalies are found in Cretaceous-Tertiary boundary sediments which strongly supports the impact theory and suggests that the impactor must have been an asteroid or a comet composed of material similar to carbonaceous chondrites.

Related Topics:
Comet - Chromium - Carbonaceous chondrite

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The resulting blast would have been hundreds of millions of times more devastating than the most powerful nuclear weapon ever detonated, may have created a hurricane of unimaginable fury, and certainly would have thrown massive amounts of dust and vapor into the upper atmosphere and even into space. A global firestorm may have resulted as the incendiary fragments from the blast fell back to Earth. Analyses of fluid inclusions in ancient amber suggest that the oxygen content of the atmosphere was very high (30 - 35%) during the late Cretaceous http://minerals.cr.usgs.gov/gips/na/0amber.htm#amber. This high O2 atmospheric content would have supported massive combustion. The level of atmospheric O2 plummeted in the early Tertiary. In addition the worldwide cloud would have choked off sunlight for years, resulting in a "long winter" that wiped out many existing species, as well as creating "acid rains" that would have inflicted further hardship on the environment.

Related Topics:
Fluid inclusions - Amber - Oxygen

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Although further studies of the "Cretaceous-Tertiary" or "K-T" layer consistently showed the excess of iridium, the idea that the dinosaurs had been exterminated by an asteroid remained a matter of controversy among geologists and paleontologists for over a decade.

Related Topics:
Geologist - Paleontologist

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