Extinction is the complete disappearance of a species from Earth. It is a natural part of evolution, but it occurs at varying rates.
The standard, low-level rate of extinction that occurs continuously throughout geological time. It is usually caused by local environmental changes, competition, or gradual loss of habitat.
A widespread and rapid decrease in biodiversity on Earth. It involves the loss of a large percentage of all living species across various groups within a relatively short geological period.
Earth has witnessed five major mass extinction events (the "Big Five").
| Event | Period | Major Impact |
|---|---|---|
| Permian Extinction | End of Permian | The "Great Dying"; ~96% of marine species lost. |
| K-T Extinction | End of Cretaceous | Extinction of Dinosaurs; allowed for the rise of mammals. |
The K-T boundary is a thin layer of sediment found worldwide, marking the end of the Mesozoic Era. It is famous for the Alvarez Hypothesis, which suggests a massive asteroid impact caused the extinction of non-avian dinosaurs.
George Gaylord Simpson, a key figure in the Modern Synthesis, explained how higher taxonomic groups (Families, Orders, Classes) originate through Quantum Evolution.
There are two primary models regarding the tempo of evolution.
The traditional Darwinian view that evolution occurs at a constant, slow, and steady rate. Transformation is continuous and incremental.
Proposed by Niles Eldredge and Stephen Jay Gould. It suggests that species remain stable for long periods (stasis), "punctuated" by brief periods of rapid change during speciation.