The 2010 TIME 100

Describing the fossil record, Charles Darwin wrote that "the crust of the earth is a vast museum." For 150 years, paleontologists have been searching that collection. Few expeditions have matched those of the team led by Tim White, 59, of the University of California, Berkeley.

Since 1981, they have collected thousands of fossils from a valley in Ethiopia whose sediments span 6 million years. Their masterpiece, unveiled last October, is a 4.4 million-year-old skeleton of Ardipithecus ramidus — the oldest and most complete in the human family, predating Lucy by 1.2 million years.

"Ardi," a 4-ft. female, transforms our picture of our early ancestors. Ardi was at home in trees, but she also walked upright. A woodland dweller, she refutes the belief that modern posture was an adaptation to living on the savanna. Gaps in human history remain, but White has filled a big one.

Carroll is the author of Remarkable Creatures: Epic Adventures in the Search for the Origins of Species

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