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Skyrocketing animal diversity a half-billion years ago was linked to spikes and dips in marine oxygen levels, according to a detailed geological study.
Researchers hope that the genes of a glowing squid can illuminate how animals evolved organs for beneficial bacteria.
Layered deposits of coral skeletons hold vast stores of environmental data from thousands of years ago, including annual records of ocean temperatures, water pollution and storm activity.
For decades, researchers have commonly assumed that higher oxygen levels led to the sudden diversification of animal life 540 million years ago. But one iconoclast argues the opposite: that new animal behaviors raised oxygen levels and remade the environment.