When paleontologist refer to the "big five" to what are they referring?

When paleontologist refer to the "Big Five" they are referring to the big five mass extinction events that had happened on Earth.

Explanation:

The five events;

The Ordovician-Silurian extinction event

The (Late) Devonian extinction event

The Permian-Triassic extinction event

The Triassic-Jurassic extinction event

The Cretaceous-Tertiary extinction event

dz nuts.   eeneneneeenenne

volcanoes (an event in the geosphere) release a large amount of particulate matter into the atmosphere. these particles serve as nuclei for the formation of water droplets (hydrosphere). rainfall (hydrosphere) often increases following an eruption, stimulating plant growth (biosphere).