A unit of time in geological history defined by the existence of a specific organism or fossil group.
From bio- 'life' + Greek chronos 'time.' Developed in paleontology to measure geological epochs not by years but by the lifespan of characteristic species.
Scientists realized they could read Earth's timeline like a book where species are the chapters—the 'Age of Dinosaurs' is essentially a biochron, a time period named for which creatures dominated.
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