Nemesis

Nemesis and the 26-Million-Year Clock

In 1984 two paleontologists counting fossil families found a rhythm in the extinction record: a beat arriving every 26 million years. Astronomers worked out what could keep time like that, named it Nemesis, and went looking. Forty years of infrared surveys have not turned it up. The beat has survived every attempt to explain it away, including a rewrite of the geological timescale underneath it.