Carl Sagan was American astronomer who popularized science and tried to make it more accessible to the public. Sagan dedicated his whole live in reasearch of areas like astronomy, cosmology, planetary science, space exploration, and the philosophy of science, but he was especially interested in the origin of life on Earth and in the possibility of life elsewhere in the universe (Astrobiology). He also worked to bring science to the public through lectures, television shows, and popular books. In the late 1960s Sagan helped show that the variations in color on the surface of the planet Mars were not caused by the presence of life. Earlier observers of Mars had suggested that the dark, greenish areas might be vegetation of some sort. Sagan proposed that the dark areas were hills, which the Martian wind stripped of the finer, lighter-colored dust particles that collected in the valleys. Sagan’s theory was confirmed by the Mariner 9 spacecraft’s visit to Mars. During the 1970s Sagan studied the present atmosphere of Earth. He studied the way that winds circulated dust through the atmosphere and how large amounts of dust, such as that from volcanic explosions, might affect Earth’s climate. His study of Earth’s atmosphere led him to formulate the idea of nuclear winter with American scientists Paul and Anne Ehrlich in the 1980s. Sagan and the Ehrlichs theorized that the dust and ash thrown into the atmosphere by the explosions of a nuclear war and the ensuing fires might be so thick and widespread that it would block the Sun’s light for months or years. The damage that a nuclear winter would cause to crops and Earth’s ecosystems would be at least as devastating as the nuclear explosions. The idea of nuclear winter was met with much controversy, and scientists have continued debating the theory. He won the 1978 Pulitzer Prize for his book The Dragons of Eden: Speculations on the Evolution of Human Intelligence. In 1980 Sagan cowrote and hosted...
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