Glossary Database

Select a Letter to view the associated terms.
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

 Glossary Term: 

Definition:

 Mafic  A mineral or rock rich in iron and magnesium silicates such as olivine and pyroxene.
 Magma  Molten rock, generally a silicate melt with suspended crystals and dissolved gases.
 Magma chamber  A reservoir of magma in the shallow part of the lithosphere from which volcanic materials are derived; the magma has ascended into the crust from an unknown source.
 Magmatic differentiation  A general term for the processes by which magmas differentiate. It includes fractional crystallization, magma mixing, and assimilation.
 Magmatic segregation  Separation of crystals of certain minerals from a magma as it cools. For example, some minerals (including certain valuable metals) crystallize while other components of the magma are still liquid. These early-formed crystals can settle to the bottom of a magma chamber and thus become concentrated there, forming an ore deposit.
 Magnetic anomaly  A deviation of observed magnetic inclination or intensity (as measured by a magnetometer) from a constant normal value.
 Magnetic field  The region of influence of a magnetized body or an electric current.
 Magnetic pole  Either of two areas near opposite ends of a magnet where the magnetic intensity is greatest.
 Magnetic reversal  A complete 180-degree reversal of the polarity of Earth's magnetic field.
 Magnetosphere  A region of the extreme upper atmosphere that is dominated by the magnetic field and charged particles are trapped in it. It acts as a type of radiation shield.
 Magnitude  A measure of the size of an earthquake, usually calculated from the common logarithm of the largest ground motion observed and corrected for distance from the earthquake focus.
 Mantle  1.) The zone of Earth's interior between the base of the crust (the Moho discontinuity) and the core. 2.)The back, wings, and scapulars of a bird (Morris 1992).
 Mantle plume  A buoyant mass of hot mantle material that rises to the base of the lithosphere. Mantle plumes commonly produce volcanic activity and structural deformation in the central part of lithospheric plates.
 Marble  A metamorphic rock consisting mostly of metamorphosed limestone or dolomite.
 Mare (pl. maria)  Any of the relatively smooth, low, dark areas of the Moon. The lunar maria were formed by extrusion of lava.
 Marine  Pertaining to the oceans.
 Mass  A measure of how much matter an object contains.
 Mass movement  The transfer of rock and soil downslope by direct action of gravity without a flowing medium (such as a river or glacial ice). Synonymous with mass wasting.
 Mass wasting  The downslope movement of material under the influence of gravity.
 Mast  the fruit of forest trees such as oak and beech used as fodder for hogs and other animals (Morris 1992).
 Matrix  The relatively fine-grained rock material occupying the space between larger particles in a rock. See also groundmass.
 Matter  Anything that has mass and takes up space.
 maxilla (maxillary)  Paired bone of upper jaw that lies just above (or behind) the premaxilla.
 Maxillary teeth  Teeth located on the two principal dermal bones of the upper jaw in reptiles and amphibians (Peters 1964).
 Meander  Broad, looping bend in a river.
 Mechanical weathering  The breakdown of rock into smaller fragments by physical processes such as frost wedging. Synonymous with disintegration.
 medial  Toward the middle.
 Medial moraine  A ridge of till formed in the middle of a valley glacier by the junction of two lateral moraines where two valley glaciers converge.
 Melange  A mixture of diverse deformed rocks formed in the accretionary prism at a convergent plate margin.
 Melanistic  is a term that refers to the black color phase of some mammals. For example, some populations of marmots are melanistic or black.
 melanophores  Black pigment cells.
 Melt (silicic melt)  A liquid, fused rock.
 Melting  The temperature at which a solid phase changes to a liquid phase.
 Menziesia  a type of shrub
 Mercalli scale  A measure of earthquake intensity determined from the effects on people and buildings, ranges from I (low) to XII (nearly total destruction).
 Mesa  A flat-topped, steep-sided high-land capped with a resistant rock formation. A mesa is smaller than a plateau but larger than a butte.
 Mesic  1. Of or relating to organisms that require moderate amounts of moisture. 2. describing a habitat with moderate moisture (Morris 1992) 3.) Medium; moderate; when pertaining to climate means moderate temperatures.
 Mesosphere  Belt of atmosphere, just above the stratosphere, from 30-50 miles(50-80km) above the earth.
 Mesozoic  1. the geologic era extending from the end of the Paleozoic era to the beginning of the Cenozoic era, dating form approximately 225 to 65 million years ago; included the Triassic, Jurassic, and Cretacious Periods. 2. the rocks formed during this era (Morris 1992). 3.)The era of geologic time from the end of the Paleozoic Era (225 million years ago) to the beginning of the Cenozoic Era (65 million years ago). View timeline of geologic events.
 Metabasalt  A basalt that has been metamorphosed.
 Metaconglomerate  A metamorphosed conglomerate.
 Metallic bond  A chemical bond in which shared electrons move freely among the atoms.
 Metamorphic   any rock derived from pre-existing rocks by mineralogical, chemical and/or structural changes; process of metamorphism
 Metamorphic rock  Any rock formed from preexisting rocks by solid state recrystallization driven by changes in temperature and pressure and by chemical action of fluids.
 Metamorphism  Alteration of the minerals and textures of a rock by changes in temperature and pressure and by a gain or loss of chemical components.
 Meteorite  Any particle of solid matter that has fallen to Earth, the Moon, or another planet from space. Compare to asteroid.
 Mica  A group of silicate minerals exhibiting perfect cleavage in one direction.
 Microcontinent  A relatively small, isolated fragment of continental crust. Example: Madagascar.
 Microtopography  topography on a smaller scale
 Middens  a large refuse heap containing such materials discarded materials, food remains, bones, and so on (Morris 1992).
 Midocean ridge  Broad fractured swell in the ocean basins. New oceanic crust is formed at this type of divergent plate boundary. Synonymous with oceanic ridge.
 Migmatite  A mixture of igneous and metamorphic rocks in which thin dikes and stringers of granitic material interfinger with metamorphic rocks.
 Migrate  To travel at regular intervals in large numbers in a particular direction, typically north or south.
 Migration  1. in general, any movement of an animal from one location to another. 2. specifically, a predictable, recurring group movement that is characteristic of the members of a given species, and that occurs regularly in response to seasonal changes in temperature, precipitation, and so on (Morris 1992)
 migration corridor  The path of rivers and streams followed by salmon in their journeys to and from natal (hatching grounds)streams.
 milt  Male salmon sperm and semen.
 Mine Tailings  the decomposed outcrop of a bed or vein of valuable material (Morris 1992).
 Mineral  A naturally occurring inorganic solid having a definite internal structure and a definite chemical composition that varies only within strict limits. Chemical composition and internal structure determine its physical properties, including the tendency to assume a particular geometric form (crystal form).
 Mineralogy  The study of minerals. Their formation, occurrence, composition, and properties.
 Miogeocline  A prograding wedge of shallow water sediment at the continental margin.
 Mitochondria  self-replicating organelles, bounded by two membranes, that are found in the cytoplasm of all eukaryotic cells and produce cellular energy in the the form of ATP via the oxidative phosphorilation reactions (Morris 1992).
 Mohorovicic discontinuity  The first global seismic discontinuity below the surface of the Earth. It lies at a depth varying from about 5 to 10 m beneath the ocean floor to about 35 km beneath the continents. Commonly referred to as the Moho.
 Moh's relative hardness scale  A scale of mineral hardness divided into 10 steps using a common mineral, determined by scratching the sample with some common item such as a penny or nail.
 Molecule  The smallest amount of chemical substance that can exist alone. It is made of two or more atoms.
 Molt  1. to shed hair, outer skin, feathers, or horns before replacement of parts of new growth. 2. an act, instance, or process of molting (Morris 1992). 3.)The shedding of the exoskeleton (skin) of a caterpillar allowing for growth. Caterpillars experience several molts before pupating.
 Molten  Melted by heat.
 Monocline  A bend or fold in gently dipping horizontal strata.
 Monoestrus  refers to a mammal having only one estrus cycle in a year. Elk are a good example.
 Monogamous  Prolonged and exclusive pair bond with a single member of the opposite sex in order to raise young (Gill 1995).
 Monogamy  a mating pattern in which males and females are paired one to one for at least one reproductive season usually associated with parental care by both parents (Morris 1992).
 Moraine  A mound or ridge of till deposited directly by glacial ice.
 Morph  A distinct, readily observeable type of a given species. For example, within the species Colias occidentalis, there are both yellow and orange morphs.
 Mortality  refers to death rate. We often use the term mortality factors, which are factors that cause the death of an animal. Starvation could be a mortality factor.
 Mountain  A general term for any landmass that stands above its surroundings. In the stricter geological sense, a mountain belt is a highly deformed part of Earth's crust that has been injected with igneous intrusions and the deeper parts of which have been metamorphosed.
 Mud  A mixture of water with silt- or clay-sized earth material, ranging from semi-fluid to soft and plastic.
 Mud crack  A crack in a deposit of mud or silt resulting from the contraction that accompanies drying.
 Mudflow  A flowing mixture of mud and water.
 Mudstone  A sedimentary rock composed of mineral fragments finer than those in a siltstone.
 Multi-ring basin  A large crater (on the Moon they are more than 300 km in diameter) containing a series of concentric ridges and depressions. Example: the Orientale basin on the Moon.
 Muskeg  1. a bog characterized by scattered and stunted evergreens. 2. broadly, any area of wetland vegetation (Morris 1992).
 Mycorrhizal Fungi  the symbiotic relationship between certain nonpathogenic or weakly pathogenic fungi and the living cells of roots of certain higher plants (Morris 1992).
 Mylonite  A foliated metamorphic rock formed by intense shearing and deformation of preexisting grains. Formed in the transition between brittle fracture and ductile flow.