A type of igneous rock that is made mostly of dense, dark minerals, such as olivine and pyroxene.
magma
Molten rock deep inside the Earth.
magma chamber
A region below a volcano where magma and gases collect.
magnetic field
A field produced by a magnetic object that exerts a force on other magnetic materials or moving electrical charges. Earth’s magnetic field behaves as if a magnet were contained within the planet.
magnetic polarity
The direction of the Earth’s magnetic field. A compass today will point north, which is normal polarity; south is reversed.
magnetite
A magnetic mineral that takes on Earth’s magnetic polarity as it crystallizes.
magnetometer
An instrument that measures the magnetic field intensity.
magnetosphere
Charged particles beyond the atmosphere that are held in place by Earth’s magnetic field.
main sequence star
A star that is fusing hydrogen atoms to helium; a star in the main portion of its “life.”
manganese nodule
Rocks on the seafloor that contain valuable minerals, especially manganese.
mantle
The middle layer of the Earth; made of hot rock that circulates by convection.
map
A 2-dimensional representation of Earth’s surface.
maria
The dark parts of the Moon’s surface, made up of ancient basaltic eruptions.
marine regression
The falling of sea level so that seas no longer cover the continents.
marine transgression
The rising of sea level over the continents.
maritime climate
A moderate climate dominated by a nearby ocean.
marsh
A shallow wetland with grasses and reeds, but there no trees. Water may be fresh, saline, or brackish.
mass movement
Erosion in which soil or rock move downslope due to gravity.
mass wasting
Erosion in which soil or rock move downslope due to gravity.
mathematical model
A set of mathematical equations that simulates a natural system.
meander
A bend or curve in a stream channel.
mechanical weathering
Weathering that breaks rocks into smaller pieces without altering their chemical composition.
medial moraine
Lateral moraines that join together within a main glacier as tributary glaciers merge.
mesosphere
Layer between the stratosphere and thermosphere; temperature decreases with altitude.
metabolism
The chemical work of cells; the chemical reactions a living organism needs to live, grow and reproduce.
metamorphic rock
A rock that forms from a previous rock that is exposed to heat and/or pressure.
metamorphism
A solid state change in an existing rock due to high temperature and/or pressure that creates a metamorphic rock.
meteor
Material from outer space that burns up as it enters Earth’s atmosphere.
meteor shower
An area of frequent meteors appearing to originate in a particular part of the sky.
meteorite
Fragments of planetary bodies such as moons, planets, asteroids, and comets that strike Earth.
meteoroid
A small rock in interplanetary space that has not yet entered Earth’s atmosphere.
microbe
A microorganism.
microclimate
A local climate that is different from the regional climate.
microcontinent
A fragment of crust that is smaller than a continent.
microfossil
A fossil that must be studied with the aid of a microscope.
microwave
The shortest wavelength radio waves.
mid-latitude cyclone
A cyclone that forms in the middle latitudes at the polar front.
mid-ocean ridge
A large, continuous mountain range found within an ocean basin. It is the location on the seafloor where magma upwells and forms new seafloor.
Milankovitch cycles
Cycles adding up to variations of around 100,000 years regarding Earth’s position relative to the Sun that affect global climate.
Milky Way Galaxy
The spiral galaxy in which Earth and our solar system reside.
mineral
A naturally occurring inorganic, crystalline solid with a characteristic chemical composition.
mineralogist
A scientist who studies minerals.
model
A representation of an object or system that is easier to study and manipulate.
mold
An impression made in sediments by the hard parts of an organism.
molecular mass
The mass of all the atoms in a molecule.
molecule
The smallest unit of a compound; it is made of atoms.
monocline
A bend in a set of rocks that causes them to be inclined relative to the horizontal.
monsoon
Hot land draws cool air off a nearby sea creating large winds and often rain.
moon
A celestial object that orbits a planet.
moraine
Linear deposit of unsorted, rocky material on, under, or left behind by glacial ice.
mountain breeze
A wind that blows from a mountain to a valley at night when mountain air is cooler.
mouth
Where a stream enters a larger body of water such as a lake or an ocean.
mudflow
Saturated soil that flows down river channels.
mutation
A change in the genetic makeup of a population of organisms that can be beneficial, harmful, or neutral.
mutualism
A symbiotic relationship between two species in which both species benefit.