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Welcome to the Cenozoic (SEN-ohZO-ic) era! This is the time after the dinosaurs. It began around 65 million years ago. So what happened to all the dinosaurs? Well, around this time, all the dinosaurs died out. In just a few thousand years, 70% of the earth’s species became extinct. Many smaller creatures including fish, plant life and mammals survived and are still with us today. But the great Age of the Dinosaurs was over. It happened so quickly that we call it an “extinction event”. We call this great extinction the “K/T Boundary”. But why did the dinosaurs die? And how did it happen so quickly? No one really knows for sure.

Most scientists agree that the earth became a lot colder around this time. The land areas – which were now separated into many continents - developed seasons. This means that instead of it being hot and dry all year long, there were winters and summers. But this does not explain why so many animals died so quickly. One theory is that a lot of volcanoes were active. When a volcano erupts, it spews ash and carbon dioxide into the air, which creates a thick, black cloud. This cloud can block out the sun and cause many of the plants to die. When the plants die, the dinosaurs don’t have anything to eat. The cloud would also have made the earth a lot colder. And since dinosaurs needed the sun to stay warm, they would freeze. Only the smaller creatures - mammals, fish and reptiles - would be able to live in the cold.

Another theory involves a huge meteorite falling to the earth. Scientists believe that about 65 million years ago, a chunk of rock about 12 miles wide fell into the sea by the Yucatan platform in Mexico. As the meteoroid fell to the earth, dust and carbon filled the air and blocked out the sun. Smaller meteors rained down on the planet as the giant rock broke up in the earth’s atmosphere. When the largest chunk hit the earth, it caused a wall of water to rise up five miles high, starting large waves and flooding all over the planet. On the northern continents, the heat caused by this impact started terrible fire storms. The “crater”, or great dent made by the meteor, is still in the northern part of Yucatán peninsula today. It is 90 miles wide and 125 miles across! This theory is called the “Bolide Impact” theory.

Pieces of rock show a change in the earth’s climate during this time. This is an important clue to the mystery of the dinosaurs’ disappearance. Scientists have discovered a layer of iridium in the rocks from the end of the Cretaceous period. Iridium is a rare mineral on earth, but it’s more common in outer space. Near the crater, scientists have also found pieces of shocked quartz. These are rocks that have been under great pressure and high heat. Many scientists believe that they were shaped by the meteor. We may never know what caused the dinosaurs to die, but scientists will continue to study the K/T boundary for years to come.






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