Mammuthus columbi, the Columbian mammoth, used to be common in America, but went extinct about 10,000 years ago. The specimen found south of Dallas is estimated to be 20,000 - 40,000 years old. Illustration by Karen Carr/Perot Museum of Nature and Science hide caption

itoggle caption Illustration by Karen Carr/Perot Museum of Nature and Science

The photographer Sebastiao Salgado, in New York City on Thursday, says we are at a "special moment" — our world now needs to be protected from climate change and other forces. Misha Friedman for NPR hide caption

itoggle caption Misha Friedman for NPR