Three million years may seem like a long time. But when you consider that planet Earth is more than 4.5 billion years old, it is a pretty short period of time.
The blue whale, （weigh） more than even the biggest dinosaurs, is the largest animal has ever lived. They can grow to 30 meters long and be as heavy as 130, 000 kilograms. But for millions of years, they were not nearly that large, scientists said. "All of a sudden-'boom'-we see （they） get very big, " said scientist Nick Pyenson. He and other （researcher）recently published an article on whale size. "It's like going from whales the size of minivans （面包车）to longer than two school buses," Pyenson added.
The scientists believe caused whales to get so large was a change in the Earth's climate only about 3 million years ago. This change led to food becoming more （easy） available. oncoming ice age made the ocean water cold and （bring） more nutrients, resulting in more food for large whales. Whales which were able to quickly-eat a lot of food survived, and got （large）. "Over the next three or four million years, the blue whales grew 10 times bigger than they （be）, " the scientists said.
