Humans have altered Earth so much that scientists say a new epoch in the planet's geologic history has begun. Say goodbye to the 10,000-year-old Holocene Epoch and hello to the Anthropocene. Among the major changes heralding this two-century-old man-made epoch: Vastly altered sediment erosion and deposition patterns. Major disturbances to the carbon cycle and global temperature. Wholesale changes in biology, from altered flowering times to new migration patterns. Acidification of the ocean, which threatens tiny marine life that forms the bottom of the food chain. The idea, first suggested in 2000 by Nobel Prize-winning chemist Paul Crutzen, has gained steam...