The greatest extinction event in Earth's history, the Latest Permian Extinction, saw a loss of more than 90% of the planet's species. Second to the mystery of what caused this extinction is why life on Earth took a prolonged five-million years to recover (referred to as the Early Triassic period).
Previous work has suggested that the world's oceans had remained anoxic and uninhabitable during this time (no dissolved oxygen in sea water for life). However, this new work by S.E. Grasby and colleagues demonstrates that Earth's oceans quickly returned to habitable conditions and were then driven back to anoxia several times during the Early Triassic.
This caused several failed attempts by life to recover until the age of the dinosaurs finally began. The cause of these repeated stresses remains uncertain, but Grasby and colleagues point to evidence for a series of major volcanic eruptions during that time.
They suggest that emissions of volcanic gases in addition to nutrients and toxins could have had significant and repeated impacts on the global ecosystem.
Paper: S.E. Grasby et al., doi: 10.1130/G33599.1