The Cretaceous–Tertiary (K–T) extinction event, also known as the K–T event, was a mass extinction of some three-quarters of the plant and animal species on Earth that occurred over a geologically short period of time, approximately 66 million years ago. It marked the end of the Cretaceous period and with it, the entire Mesozoic Era, opening up the Cenozoic Era that continues today.
In the geologic record, there is evidence for at least two major periods of mass extinction. The first occurred at the boundary between the Permian and Triassic periods 251.4 million years ago (Mya), when an estimated 90% to 96% of all marine species and 70% of terrestrial vertebrate species became extinct in what is popularly known as “The Great Dying” or “The Permian–Triassic Extinction Event”. The second major episode happened 65.5 Mya during which 83% of all marine species and about 50% or more of all terrestrial vertebrate species were extinguished in what is commonly referred to as “The Cretaceous–Tertiary Extinction Event” or simply “The K-T Event”.
Of particular interest to scientists investigating this event is its timing; both extinctions happened relatively quickly, at least in geological terms. In addition, they both coincide with large-scale changes in Earth’s climate and geography: The Pangean supercontinent began breaking apart into today’s continents during the late Triassic; while during most of early Cretaceous time Earth was dominated by a single landmass called Laramidia that lay south of an inland sea called Tethys Ocean. Both episodes also have been linked to asteroid impacts: It has long been suspected that an impact played a role in causing The Great Dying—and recent evidence suggests that an asteroid may indeed have caused widespread devastation at exactly the right time to explain this ancient mystery. As for whether an impact caused The K-t Event… well, scientists are still debating that one!
What is certain is that something dramatic happened around 65.5 million years ago—something so catastrophic that it led to one of the biggest mass extinctions earth has ever seen. Here’s a look at some key facts about this fascinating moment in history:
– On behalf of an outstanding scientist