Geography

Plate Tectonics Definition Plate tectonics is a theory that the Earth’s lithosphere (the crust and upper mantle) is divided into a number of large, platelike…

Earthquake Definition Earthquake is a sudden movement of the Earth’s lithosphere (its crust and upper mantle). Earthquakes are caused by the release of built-up stress…

Seismic Wave Definition Seismic wave is an elastic shock wave that travels through the earth, as from an earthquake or explosion; also, one of four…

Continental Crust Definition Continental crust is the solid, outermost layer of the Earth, lying above the mantle.  This layer is sometimes called sial because its…

Metamorphism Definition Metamorphism is the process by which rocks are changed in composition, texture, or structure by extreme heat and pressure. The change occurs primarily…

Metasomatism Definition Metasomatism is the process by which the chemical composition of a rock is changed through the introduction or extraction of chemicals dissolved in…

What is Permafrost? Permafrost is a thick subsurface layer of soil that remains frozen throughout the year, occurring chiefly in Polar Regions. It is defined…

Persian Gulf Oil The gulf has many fishing grounds, extensive reefs (mostly rocky, but also coral), and abundant pearl oysters, but its ecology has been…

Igneous Rock Definition Igneous rocks are formed by the cooling and hardening of molten material called magma. It is one of the three main rock…

Proterozoic Definition Proterozoic is the later of the two divisions of the Precambrian Eon, from about 2.5 billion to 540 million years ago. The Proterozoic…

Yangtze River, longest river in both China and Asia and third longest river in the world, with a length of 3,915 miles (6,300 kilometres). The…

Amazon River, the greatest river of South America and the largest drainage system in the world in terms of the volume of its flow and…