An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

A period of → geologic time which began at the end of the → Jurassic period approximately 145 million years ago and extended to approximately 65 million years ago.

From L. cretaceus, from cret(a) "chalk, clay," + → -aceous, because the geological remains of this period contain heightened chalk deposits.

Gacâsâ, from gac "chalk," Mid.Pers. gac + -âsâ, → -aceous.

The → mass extinction event that destroyed the dinosaurs and a majority of other species on Earth approximately 65 million years ago. This event is believed to have been the impact of a 10 km-size → asteroid or → comet nucleus and its aftereffects, including a severe → impact winter. The collision would have released the energy equivalent to 100 million megatonnes (teratonnes) of → TNT, i.e. more than 10⁹ times the energy of the atomic bomb dropped on Hiroshima on August 6, 1945. Same as the → Cretaceous-Tertiary event.

→ Cretaceous; → Paleogene; → extinction; → event.

See → Cretaceous-Paleogene extinction event.

K, representing the "→ Cretaceous period," and T the "→ Tertiary;" → event.