Lessons from History: The Big Five Mass Extinctions

If an asteroid struck Earth 66 million years ago and led to the end of the dinosaur era, then that event is identified as the Cretaceous-Paleogene extinction.

If the Permian event resulted in the loss of roughly 96% of marine species and 70% of land species, then it stands as the most devastating of all the big five mass extinctions.

If iridium is rare in Earth's crust but common in asteroids, then finding a global layer of it suggests a massive impact occurred during the K-Pg extinction.

If scientists categorize the most significant drops in biodiversity over the last 500 million years, then the first four listed are included; however, the Holocene is the current era and is not part of the historical "Big Five."

If a massive ice age occurred and locked water into glaciers, then sea levels dropped and destroyed shallow marine habitats. If these habitats vanished, then the Ordovician-Silurian extinction followed.

If the majority of early life forms lived in the sea during the Ordovician and Devonian periods, then the big five mass extinctions would show their greatest impact on marine fossil records.

If we look at the geological timeline between the Triassic and Jurassic periods, then the data shows a major extinction pulse occurred about 201 million years ago.

If the Permian extinction was so extreme that it nearly wiped out all life on the planet, then it earned the nickname "The Great Dying" among the big five mass extinctions.

If an animal was small, lived in water, or could hide underground, then it had a better chance of surviving the post-asteroid climate; however, pterosaurs and ammonites went extinct.

If current extinction rates are 100 to 1,000 times higher than the normal background rate due to human activity, then this modern loss is comparable in scale to the big five mass extinctions.

If massive algal blooms or climate shifts caused the deep water to lose its dissolved oxygen, then the resulting "anoxia" killed off many marine species.

If the Siberian Traps erupted for millions of years and released massive amounts of CO2, then the resulting global warming would trigger the Permian-Triassic event, one of the big five mass extinctions.

If an extinction clears out old competitors, then the survivors have room to expand. If survivors expand into new roles, then we see rapid evolution and the rise of new dominant groups.

If a rock layer is full of specific fossils and the layer immediately above it is empty or has different species, then a mass extinction occurred in that timeframe.

If a massive percentage of life is lost, then the slow process of natural selection and speciation is required to rebuild the ecosystem. If this process is slow, then it takes millions of years to recover.

If the K-Pg extinction removed the large dinosaurs that occupied most niches, then small mammals were free to evolve into those empty roles. If mammals filled those roles, then they became the new dominant group.

If these marine invertebrates were the dominant life forms in the Ordovician, then they would suffer the most during a sea-level drop; humans and flowering plants did not exist yet.

If trilobites had been declining for millions of years and the Permian event was the most severe of the big five mass extinctions, then it provided the final blow that made them extinct.

If many new ecological roles become available at once and survivors change to fit them, then the species "radiate" into new forms. This is called adaptive radiation.

If the big five mass extinctions were triggered by volcanoes, ice, and space rocks, then the history of life is shaped by large-scale physical changes to the planet.