Crown of Thorns Starfish, which dine on the live coral polyps, can decimate the living coral veneer as they migrate over the reef. Invasions of this coral predator are an increasingly common occurrence in the Pacific Ocean. Paleoceanographers figured out why old reefs are found on top of mountains or deserts today, and why ancient shorelines are now submerged. This tells us that the pre-Cambrian ocean environment was very different chemically than it is today. These changes wipe out certain types of animals and allow others to flourish.
Hiatuses are also clues to catastrophic events in the history of the earth.