How the Amazon became a crucible of life

Trudging along the bank of a shallow creek in the Peruvian Amazon, Catherine Rigsby sinks knee-deep in mud. She calmly shimmies out of the muck, then grabs a branch lying on the bank for a walking stick. As stingless bees buzz around her head and macaws screech in the trees above, the sedimentologist gingerly resumes her search for a rainforest rarity: exposed rock. One of the few outcrops in this corner of the Amazon—a day’s boat ride up the Manú River from the nearest town—is around here somewhere.

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