Just before the dinosaurs first emerged, Earth suffered a mass extinction that wiped out nearly 90 percent of all species. The planet took millions of years to recover. Then, 65 million years ago, virtually all dinosaurs were wiped out in another sudden mass death. What caused their mysterious disappearance?
ATTACK FROM ABOVE
In 1980, an American scientist named Luis Alvarez made an amazing discovery. Studying rocks that formed at around the time the dinosaurs disappeared, he found that the level of iridium (a metal that’s rare on Earth but common in meteorites) was 100 times higher than normal. He found the same high level all over the world and concluded that a massive meteorite or asteroid must have slammed into Earth. Such a huge impact could have wrecked Earth’s climate and killed off the dinosaurs.
What did the meteorite do?
A huge meteorite smashing into Earth would have created a worldwide cloud of dust and fumes, choking animals and blocking out the Sun’s light and warmth. The planet’s climate would have changed dramatically, making life impossible for many species.
A meteorite produces a crater, and a meteorite big enough to change the world’s climate would produce a giant crater, so where is it? The answer came in the 1970s when scientists searching for oil found a vast crater buried more than half a mile (1 km) underground on the coast of Mexico. The space rock that left this scar was an estimated 6 miles (10 km) wide and would have hit the Earth with tremendous force, sending shockwaves all over the world.
The meteorite impact almost certainly contributed to the death of the dinosaurs, but other catastrophic events were going on at the same time, and some scientists believe that it was a chain of events rather than simply one meteorite that caused the mass extinction. Heavy volcanic activity in western India was sending up huge clouds of gas that would have contributed to climate changes.
“No land animal larger than a dog survived the mass extinction that killed the dinosaurs”
There are been five major extinctions in the past 550 million years. A mass extinction means that more than 50 percent of animal species die at one time. The mass extinction that ended the Mesozoic Era (the time of the dinosaurs) was the most recent, and more than 80 theories have been put forward to account for what happened.
DID YOU KNOW?
Not all animals perished. Those that survived included:
■ Sharks and other fish