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coal mining

(Encyclopedia)coal mining, physical extraction of coal resources to yield coal; also, the business of exploring for, developing, mining, and transporting coal in any form. Coal has been historically important indus...

solar energy

(Encyclopedia)solar energy, any form of energy radiated by the sun, including light, radio waves, and X rays, although the term usually refers to the visible light of the sun. Solar energy is needed by green plants...

Oligocene epoch

(Encyclopedia)Oligocene epoch ŏlˈəgōsēnˌ [key], third epoch of the Tertiary period in the Cenozoic era of geologic time, lasting from 38 to 24 million years ago. More of North America was dry land during the ...

Polypodiophyta

(Encyclopedia)Polypodiophyta pŏlˌēpōˌdēŏfˈətə [key], division of the plant kingdom consisting of the plants commonly called ferns. The ferns are vascular plants with stems, roots, and leaves. The small an...

Homo erectus

(Encyclopedia)Homo erectus hōˈmō ērĕkˈtəs [key], extinct hominin living between 1.6 million and 250,000 years ago, possibly as late as c.110,000 years ago. Homo erectus is thought to have evolved in Africa f...

carbon cycle

(Encyclopedia)CE5 Carbon cycle carbon cycle, in biology, the exchange of carbon between living organisms and the nonliving environment. Inorganic carbon dioxide in the atmosphere is converted by plants into sim...

teeth

(Encyclopedia)CE5 A. Upper and lower teeth of an adult B. Cross section of a molar teeth, hard, calcified structures embedded in the bone of the jaws of vertebrates that perform the primary function of masticat...

sea level

(Encyclopedia)sea level, the level of the sea, which serves as the datum used for measurement of land elevations and ocean depths. Theoretically, one would expect sea level to be a fixed and permanent horizontal su...

walnut

(Encyclopedia)CE5 Black walnut, Juglans nigra walnut, common name for some members of the Juglandaceae, a family of chiefly deciduous, resinous trees characterized by large and aromatic compound leaves. Species...

Rhodophyta

(Encyclopedia)Rhodophyta rōdŏfˈətə [key], phylum (division) of the kingdom Protista consisting of the photosynthetic organisms commonly known as red algae. Most of the world's seaweeds belong to this group. Me...