Earth Sciences Glossary

The ductile, partially molten layer of the upper mantle on which tectonic plates float and move.

A dark, fine-grained extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in iron and magnesium.

The hypothesis proposed by Alfred Wegener that continents move across Earth's surface over geologic time.

A plate boundary where two tectonic plates move toward each other, often resulting in subduction, mountain building, or volcanic arcs.

The outermost solid layer of the Earth, composed of oceanic crust (basaltic, 5-10 km thick) and continental crust (granitic, 30-70 km thick).

A plate boundary where two tectonic plates move apart, allowing magma to rise and create new crust, as at mid-ocean ridges.

The point on Earth's surface directly above the focus (hypocenter) of an earthquake.

The transport of weathered rock and sediment by water, wind, ice, or gravity.

A fracture in Earth's crust along which blocks of rock have moved relative to each other.

The preserved remains, impressions, or traces of organisms from past geologic ages, found in sedimentary rock.

A large, persistent body of dense ice that forms from the accumulation and compaction of snow and moves under its own weight.

A coarse-grained intrusive igneous rock composed mainly of quartz, feldspar, and mica; a major component of continental crust.

A location in the mantle where a plume of exceptionally hot rock rises, producing volcanic activity independent of plate boundaries.

Rock formed by the cooling and solidification of magma or lava.

The rigid outermost shell of the Earth, comprising the crust and the uppermost part of the mantle, divided into tectonic plates.

Molten rock beneath Earth's surface. When it reaches the surface through volcanic eruptions, it is called lava.

The thick layer of silicate rock between Earth's crust and core, extending from the Moho to approximately 2,900 km depth.

The transformation of existing rock into a new form through heat, pressure, or chemically active fluids without complete melting.

An underwater mountain range formed at divergent plate boundaries where new oceanic crust is created by upwelling magma.

A naturally occurring, inorganic solid with a definite chemical composition and an ordered crystalline structure.

The supercontinent that existed from approximately 335 to 175 million years ago, encompassing nearly all of Earth's landmasses.

An instrument that detects and records ground vibrations (seismic waves) caused by earthquakes, explosions, or other sources.

The branch of geology that studies rock layers (strata), their formation, composition, distribution, and succession.

The process in which one tectonic plate descends beneath another at a convergent boundary and is recycled into the mantle.

The in-place breakdown of rocks and minerals at or near Earth's surface by physical, chemical, or biological processes.