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period, in geologic time
(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...fossil fuel
(Encyclopedia)fossil fuel: see energy, sources of; fuel. ...Lepidodendron and Sigillaria
(Encyclopedia)Lepidodendron sĭjĭlârˈēə [key], two principal genera of an extinct group of primitive vascular trees. They dominated the forests of the early Carboniferous period until the ferns gained ascendan...badlands
(Encyclopedia)badlands, area of severe erosion, usually found in semiarid climates and characterized by countless gullies, steep ridges, and sparse vegetation. Badland topography is formed on poorly cemented sedime...Pitch Lake
(Encyclopedia)Pitch Lake, pool of pitch (asphalt), c.114 acres (46 hectares), SW Trinidad island, Trinidad and Tobago, near La Brea. The lake is believed to be formed and supplied by the seepage of natural pitch, a...Permian period
(Encyclopedia)Permian period pûrˈmēən [key] [from Perm, Russia], sixth and last period of the Paleozoic era (see Geologic Timescale, tablegeologic timescale, table) from 250 to 290 million years ago. Many ma...fuel
(Encyclopedia)fuel, material that can be burned or otherwise consumed to produce heat. The common fuels used in industry, transportation, and the home are burned in air. The carbon and hydrogen in fuel rapidly comb...stromatolite
(Encyclopedia)stromatolite, layered structures produced by the binding together of sediments by a thin layer of cyanobacteria. The layers, which are deposited very slowly, gradually produce rounded or hummocklike f...La Brea
(Encyclopedia)La Brea lə brāˈə [key], area, S Calif., formerly in Rancho La Brea. The La Brea asphalt pits, which yielded prehistoric animal and plant remains, are in Hancock Park, Los Angeles. The first fossil...Proconsul, in zoology
(Encyclopedia)Proconsul, extinct group of apes. Proconsul fossils have been discovered in E Africa. It had a mixture of ape and Old World monkey characteristics, and lived from 23 to 25 million years ago. ...Browse by Subject
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