When, in 1980, Luis Alvarez, a physicist, and his son Walter, a geologist, made public their theory that the dinosaurs were killed by a massive asteroid strike, it came as a curveball to palaeontologists, who believed dinosaurs had gradually died out through other means. The fa-ther-and-son team from the University of California, Berkeley, argued that evidence of the catastrophe was hiding in plain sight, the world over, as a thin layer of sediment enriched in iridium, a metal commonly found in asteroids but rare on Earth. They pointed out that no dinosaurs, with the exception of birds, were ever found beyond this critical layer and suggested a devastating impact was responsible.
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