Columbia Encyclopedia

(Encyclopedia) period, unit of time on the geologic timescale. Periods are shorter than an era and longer than an epoch. Periods are of variable length, generally lasting tens of millions of years, with characterist...

(Encyclopedia) period, in physics: see harmonic motion; wave. ...

(Encyclopedia) chalk, mineral of calcium carbonate, similar in composition to limestone, but softer. It is characteristically a marine formation and sometimes occurs in great thickness; the chief constituents of the...

(Encyclopedia) Triceratops trīsĕrˈətŏps [key] [Gr., = three-horn face], genus of ornithischian quadruped dinosaurs of the late Cretaceous period. Because of some variations in sample fossils, it was thought...

(Encyclopedia) Deinonychus dīˌnənīˈkəs [key] [Gr.,=terrible claw], swift bipedal carnivorous dinosaur of the early Cretaceous period, approximately 119–93 million years ago. Fossil specimens have been discov...

(Encyclopedia) Iguanodon ĭgwănˈədŏn [key] [Gr., = iguana tooth], herbivorous ornithiscian dinosaur, characterized by teeth similar to those of the iguana, a horny beak, spikelike thumbs, and a powerful tail...

(Encyclopedia) Velociraptor vəlŏsˈĭrăpˌtər [key] [Gr.,=swift robber], swift bipedal carnivorous dinosaur of the late Cretaceous period. It was relatively small, being approximately 6 ft (1.8 m) long. It was s...

(Encyclopedia) Louis period styles, 1610–1793, succession of modes of interior decoration and architecture that established France as a leading influence in the decorative arts. The restraint of the later Louis ...

(Encyclopedia) Paleocene epoch pāˈlēəsēnˌ [key], first epoch of the Tertiary period in the Cenozoic era of geologic time (see geologic timescale) between 60 to 66 million years ago. In W North America, the upl...

(Encyclopedia) pterosaur tĕrˈəsôrˌ [key] [Gr., = winged lizard], extinct flying reptile (commonly called pterodactyl [Gr., = wing finger]) of the order Pterosauria, common in the late Triassic and Creta...