Descriptionary

metamorphic rock rock that has changed or "meta­morphosed" into other rock through heat, pressure, or chemical processes.

metamorphism the process by which a rock is altered through heat and pressure.

microfossil a tiny fossil, often requiring study through a microscope.

mid-ocean ridge a long, elevated rise in the sea- floor, caused by the eruption of basalt and formation of new crust.

mineralization the process by which minerals infil­trate a dead organism and turn it into a fossil.

Mohorovicic discontinuity (Moho) the base of the Earth's crust, ranging from about 13 kilometers under the oceans to about 40 kilometers under the continents.

mold an impression of an organism, left behind to fossilize in rock.

monolith slender, eroded butte that eventually top­ples over.

monument a butte.

moraine a large accumulation of glacial till or drift.

oceanic trench an elongated trough on the ocean floor, caused by subduction activity.

orogeny the process by which mountains are formed.

outcrop any bedrock that has become exposed from the surrounding soil.

paleogeography the geography of a land as it was in the geologic past.

paleomagnetism Earth's magnetic field as it was in the geologic past.

Pangaea the huge, hypothetical ancient superconti- nent from which all of today's continents are thought to have split off.

Panthalassa the huge, hypothetical universal ocean surrounding the supercontinent Pangaea before it divided.

peat a deposit of decomposed plant remains from a swamp or marsh.

peneplain a flat or nearly flat land surface resulting from an advanced stage of erosion.

pingo a mound or hill, sometimes more than 100 meters high, formed by expanding permafrost, found frequently in arctic regions.

plate any one of the seven major lithospheric plates, consisting of either heavy basaltic ocean crust or lighter granitic continental crust, that cover the Earth and float on the plastic upper mantle.

plate tectonics the interaction and subsequent effects of the Earth's lithospheric plates colliding and scraping against one another.

pluton any mass of igneous rock formed beneath the Earth by the hardening of magma.

regression a recession in sea level, exposing new land.

rift a long crack in the Earth's crust.

rift valley a valley formed by faulting.

salt dome a dome formed in sedimentary rock by the upward flow of a large mass of salt.

seafloor spreading the expanding of the seafloor along mid-ocean ridges, forming new crust.

seamount a mountain under the sea.

sedimentary rock rock formed by the accumulation and bedding of silt, gravel, rocks, and organic matter, easily identified by its distinctive layering or strata.

seismic prospecting a technique of determining the nature of an underground rock structure by set­ting off explosive charges and measuring the time the shock waves take to travel varying underground paths.

seismograph an instrument that records vibrations of the Earth, particularly during an earthquake.

seismology the study of earthquakes.

sinkhole an area of ground, usually consisting of limestone or some other soluble material, that col­lapses due to water erosion.

strata collective term for layers of sedimentary rock.

stratification the layering of sedimentary rock, with changes of color or texture from one bed to the next.

stratigraphy the study of rock layers, their ages, and how they were laid down or deposited.

stratum a single layer of sedimentary rock.

subduction the descending of one lithospheric plate under another.

subduction zone the area where one lithospheric plate descends beneath another, known by a high fre­quency of earthquakes.

syncline strata bent downward in an upside-down arch; the reverse of an anticline.

taphonomy the study of the history of a fossil, from the time the organism is first preserved through when it is uncovered by a paleontologist. Skeletons, for example, may become disarticulated because of water flow, or some fossils may become flattened due to compression by a glacier or the accumulation of many layers of sediment.

tectonic referring to the actions of the Earth's crust.

terrane a piece of the Earth's crust that tears off from one tectonic plate and becomes attached to another.

thermal plume in the upper mantle, a huge column of upwelling magma located in a fixed position and therefore known as a "hot spot." Thought to be responsible for volcanic activity.

topography collective term for the layout and all of the geological features in a given area of the Earth's sur­face, including hills, mountains, valleys, lowlands, etc.