A tourist was visiting New Mexico and was amazed at the dinosaur（恐龙） bones lying about.How old are these bones? the tourist asked an elderly Native American, who served as a guide.Exactly one hundred million and three years old.How can you be so sure? inquired the tourist.Well, replied the guide, a geologist（地质学家） came by here and told me these bones were one hundred million years old, and that was exactly three years ago.