Overview 1: General

The extinction of the dinosaurs is believed to have occurred between 65 and 66 million years ago. This period is known as the K-T extinction. The K is the geological symbol for the Cretaceous period, while the T stands for the Tertiary period.

Scientists have developed many different theories to explain what happened to the dinosaurs. However, the two major theories are:

• Gradual climate change, and
• The asteroid theory
  

The Climate change theory states that: "towards the end of the Cretaceous period, the shallow seas dried up and the climate became more varied everywhere around the globe. Winters became too cold and summers too hot for dinosaurs to survive. Dinosaurs were too large to hibernate in dens, and they had no fur for protection against the cold. They also probably had difficulty cooling off in hot weather." -- World Book, 2007, Volume 5.

The Asteroid theory states that: "a large asteroid hit Earth at the end of the Cretaceous. This asteroid impact would have thrown billions of tons of dust and debris into the atmosphere. Heat from the impact may have cause huge fires worldwide. Together, the clouds of smoke and debris would have blocked sunlight from reaching the surface of the Earth for many months. Although the seeds and roots of plants had a good chance of surviving this light less period, the plants themselves stopped growing and died. Because such a catastrophe would have been severe and widespread, plant-eating dinosaurs would have starved to death. As the plant-eaters died, so did the meat eating dinosaurs that fed on them. In addition, the darkened skies caused land temperatures to drop below freezing for 6 to 12 months in many parts of the world." -- World Book, 2007, Volume 5.

Most scientists agree that no single theory completely explains why the dinosaurs suffered near complete extinction. They argue that a combination of causes attributed to the disappearance of dinosaurs.

However, scientists agree that not all dinosaurs became extinct. They regard birds as living dinosaurs that survived the extinction. We can also see the link between dinosaurs and certain modern animals, such as crocodiles and lizards.