Dinosaurs Extinction

There are different theories on dinosaurs extinction.

Sixty five million years ago, dinosaurs all suddenly died out.

Many other animals species got extinct too, but dinosaurs, once the most successful animals on the Earth, disappeared completely.

A Group of Feathered Carnivorous Velociraptors from the Cretaceous Period on Earth
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There are many different theories about why this happened, but mainly there are two ways of thinking: some scientists believe in a gradual extiniction while others believe in a more sudden extinction due to a catastrophe (even though in geological terms, "sudden" can still mean half a million years).

Artist's Concept of an Alien Planet
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Gradualists believe that because the climate had been very stable for most of the Cretaceous period, animals would have adapted to that special climate and got too specialised, so that when in the end of Cretaceous the climate started to change, it was too much for them. Others believe that the gradual movement of continents would have brought continents together and animals could get to new continents and carry diseases that the population there weren't adapted to.

Artist's Concept of the Extinction of Prehistoric Earth
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The more popular theories are those that suggest dinosaurs were wiped out by a catastrophe. When in the 1970s it was discovered that about the time when dinosaurs got extinct (in the end of the Cretaceous), there was a sediment bed that was rich in Iridium - an element that is rare on the Earth's surface, but quite common in meteorites.

Hadrosaurs Graze Peacefully as Burning Meteors Fall Through the Sky
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So a new theory suggested that a massive meteorite had struck the Earth, sending fires and shock waves, and masses of dust into the atmosphere, which blocked the sunlight out for a long time. And, on the Yukatan Penisnula in Mexico, there is a large meteorite crater that dates back from the end of Cretaceous period.

A Mighty T. Rex Roars from Overhead as a Giant Fireball Falls from the Sky
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Another theory suggests that iridium, which also is found in the Earth's mantle, could have been bought out by volcanic activity. And it is known that at the time there was quite a lot of volcanic activity, intensive enough that it could have sent enough smoke and fumes to cut out the sunlight. It has also been suggested that the meteorite and the volcanic activity together could have caused dinosaurs extinction.

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