A long, long time ago — between 378 million and 375 million years ago — about half of all species on the planet vanished. The trigger for this mass extinction, one of five known in Earth’s history, was a lethal combination of sea level rise and invasive species, according to a new study.

“The basic processes that normally result in new species forming were blocked,” study author Alycia Stigall, a paleobiologist at Ohio University, told me today.