An Etymological Dictionary of Astronomy and Astrophysics
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See → Cretaceous-Paleogene extinction event.

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

1) Third in order, rank, level, stage, formation, etc.
2) Chem.: Being or containing a carbon atom having bonds to three other carbon atoms.
3) Geology: (usually with capital initial) A term formerly used to distinguish a major period of → geologic time, from the end of the → Cretaceous period about 65 million years ago to the start of the Quaternary period about 1.6 millions years ago. The International Commission on Stratigraphy no longer sustains this term as part of the formal stratigraphic nomenclature. Instead, the → Paleogene and → Neogene periods are recommended as the primary subdivisions of the Cenozoic era.

From L. tertius, → third; → period.