Since the origin and diversification of life on Earth, there have been five episodes of mass extinction of species. How is the sixth extinction, which is in progress, different from the previous episodes ?

Mass‑extinction events in Earth’s history—such as the Ordovician‑Silurian, Late Devonian, Permian, Triassic, and Cretaceous events—were characterized by a sudden loss of many species over relatively short geological intervals.

Scientists estimate the background (pre‑human) extinction rate by examining the fossil record. Over millions of years, the average rate at which species disappear is about one extinction per million species per year (often expressed as 1 E ‑⁶ yr⁻¹).

Modern observations, however, show that human activities (habitat destruction, climate change, invasive species, pollution, overexploitation, etc.) have dramatically accelerated this rate.

Current studies compare the number of species known to be extinct in recent decades with the background rate. The calculations indicate that species are disappearing at a pace that is roughly 100 to 1 000 times faster than the long‑term natural baseline.

For example, if the natural background predicts about 0.01 species lost per year for a given taxonomic group, present data suggest a loss of 1 to 10 species per year for the same group—an acceleration of two to three orders of magnitude.

This rapid, human‑driven loss distinguishes the ongoing “sixth extinction” from the previous five mass‑extinction episodes, which were driven by natural catastrophes rather than sustained, anthropogenic pressures.

Therefore, the correct distinction is that the present species extinction rates are 100 to 1 000 times faster than in pre‑human times.