biodiversity comes and goes
This is a tiny bit odd: “A detailed and extensive new analysis of the fossil records of marine animals over the past 542 million years [says that] biodiversity appears to rise and fall in mysterious cycles of 62 million years for which science has no satisfactory explanation."
I jump for "alien tinkering" in this kind of situation, but the scientists involved are looking for things like exposure to galactic radiation as we move around the universe; Oort cloud meteor gravitational effects; planetary plumes of eruptions, and Improbable Stuff Like That.