KT Extinction

KT extinction stands for Cretaceous-Tertiary Extinction. This is a global extinction event that witnessed the elimination of about 70% of the species living on the earth within a very short time 65 million years ago. This mass extinction is known as KT extinction.

It occurred at the end of the Cretaceous period and the beginning of the Tertiary period. It ranks third in severity among the five major mass extinctions.

The theory about the KT mass extinction proposed by Louis Alvarez and his son is widely accepted theory. They stated that an asteroid about 15 km in diameter hit the earth forming a crater at the tip of the Yucatan Peninsula in Mexico. This crater is known as Chicxulub crater.

The impact of the crater is believed to have penetrated the earth’s crust which released a large amount of dust and debris into the atmosphere and led to tsunami, fires, wind storms, acid rains, and volcanic activities. The dust must have blocked the sunlight coming to the earth which would have lowered the earth’s temperature.

90% marine species, 50% of marine genera, 85% of land species, and 56% of land genera got extinct as a result of KT extinction. This catastrophic event marked the advent of the mammalian age.

Dinosaurs form the major group of animals that got extinct during this period. However, it is not proved that the asteroid attack killed the dinosaurs. Many species of dinosaurs have diminished millions of years after the KT extinction.

The group of reptiles comprising birds, dinosaurs, and crocodilians survived the extinction and evolved into modern birds and crocodiles. Among the marine flora and fauna, only 13% of the planktons remained alive.

Also read: Evidence of Evolution

Sometimes the remains of the dead organisms are preserved as fossils. The evidence for the KT extinction can be obtained by comparing the fossils found at the end of the Cretaceous period to that at the beginning of the Tertiary period.

KT Boundary

The point between the Cretaceous (K) and the Tertiary (T) period is known as the KT boundary. This period has been dated to 65.5 million years ago by geologists. The geologists have discovered that the KT boundary has a very high concentration of iridium than normal. The iridium concentration found in the KT boundary is similar to that in the meteorites.

It was estimated that the asteroid that hit the earth would have been 10 km in diameter releasing immense energy. It not only destroyed a region up to thousands of kilometres but also formed a cloud of dust that interrupted the sunlight reaching the earth’s surface for years. The plants, the main basis of the food chain could not survive and eventually, the dinosaurs died.

Also read: Extinction

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Frequently Asked Questions on KT Extinction


What organisms lived during the Cretaceous period?

The Cretaceous period is dominated by dinosaurs, large reptiles and flying reptiles. Flowering plants also appeared in this period.


What organisms lived during the Tertiary period?

The mammals evolved dramatically in the tertiary period.


What are the eras the KT period belongs to?

The Cretaceous period belongs to the Mesozoic era and the tertiary period belongs to the Cenozoic era.

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