Over Earth's long history, there have been a number of times when ice and snow covered a large part of its surface. Such periods are known as ice ages.

　　Earth is in an ice age now. It started about 2 million years ago. Despite the many warm periods since then, scientists regard the whole time as one ice age because of the continuous existence of at least one large ice sheet—the one over Antarctica.

　　The new discovery was made by Chinese and US scientists. It suggests Peking Man is probably our oldest cold weather human being, said Darryl Granger, an atmospheric scientist at Purdue University whose research appears in Thursday's edition of the journal Nature.

　　The average yearly temperature at the time in that part of China was around the freezing mark, but it was too dry for an ice sheet, Granger said.

　　This raises a question. How did Peking Man survive the cold weather?

　　Rick Potts, a Smithsonian Institution human origins expert who wasn't involved in the research, raised three possibilities：

　　First, fire. Early findings showed signs of a fire in Peking Man's cave. But there has been debate about whether the fire was accidental or controlled.

　　Second, fur. There is no evidence that Peking Man used simple tools to make more form­fitting clothes. It's more likely he wore animal fur.

　　Lastly, he may have developed gradually to handle the cold. Peking Man may have experienced physiological changes that allowed more blood to flow to his hands and legs, Potts said. “People in general who live in colder climates tend to be shorter and wider，” he explained.

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