The record from the seafloor

Anton Petrov points to an r-process event. That's neutron capture associated with the "kilonova" merger of neutron-stars. Some of the physics was fine-tuned last month.

Kilonovae be rare these days. This one happened 100-90 Mya. They can tell from the decay of Plutonium-244, actually fairly long lived, but rare here because most of our plutonium is made: for critical-mass. Kilonova should also create Curium-247 but this one has run out already.

As a side note, the Iron-60 spikes from 7 and 2 Mya are also found. And better-constrained, they say.