We like to believe that, in our lifetime, the human condition is improving.
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In coastal waters rich in runoff, plankton can swarm densely, a million in a drop of water. They color the sea brown and green where deltas form from big rivers, or cities dump their sewage. Tiny yet hugely important, plankton govern how well the sea harvests the sun's bounty, and so are the foundation of the ocean's food chain.