This list includes 82 Earth science words that start with M, from “Maar” to “Mylonite”. They cover landforms, rocks, processes, and climate terms used in teaching, mapping, and fieldwork.
Earth science words that start with M are concise technical terms and names used to describe Earth’s features and processes. For example, “maar” names a type of volcanic crater important in European geological studies.
Below you’ll find the table with Term, Definition, Category, Example, and Further reading.
Term: Lists the word itself; you can scan spelling and alphabetical order to find specific entries quickly.
Definition: Provides a concise one- to two-sentence meaning so you understand the concept without specialist background.
Category: Shows the broad field or type, like “landform” or “mineral”, helping you filter terms by subject area.
Example: Gives a short real-world instance or use so you see how the term appears in studies or maps.
Further reading: Links to reputable articles or glossaries so you can explore longer explanations and authoritative definitions.
Earth science words that start with M
| Term | Category | Related field | Typical scale/units |
|---|---|---|---|
| Magma | Molten rock | Geology/Volcanology | centimeters to kilometers; 700–1,300 °C |
| Magma chamber | Subsurface reservoir | Volcanology/Geology | hundreds of meters to tens of kilometers |
| Magmatism | Geologic process | Geology/Volcanology | regional to global; millions of years |
| Mafic | Rock composition adjective | Petrology/Geology | chemical composition; common minerals |
| Maar | Volcanic crater | Volcanology/Geomorphology | tens to hundreds of meters diameter |
| Magmatic intrusion | Geologic structure/process | Igneous petrology/Geology | meters to kilometers |
| Mantle | Earth layer | Geology/Geophysics | depth ~35–2,900 km |
| Mantle plume | Thermal upwelling | Geophysics/Volcanology | tens to hundreds of kilometers wide |
| Mantle convection | Solid-state flow process | Geophysics | regional to global; millions of years |
| Magnetic field | Planetary field | Geophysics | microteslas (µT); global |
| Magnetosphere | Space environment | Space physics/Geophysics | tens of thousands of km |
| Magnetic anomaly | Geophysical feature | Geophysics/Geology | nanoteslas to microteslas; local to regional |
| Magnetic declination | Measurement/phenomenon | Geophysics/Navigation | degrees (°) |
| Magnetic inclination | Geomagnetic angle | Geophysics | degrees (°) |
| Magnetic reversal | Geomagnetic phenomenon | Geophysics | timescales: thousands to millions of years |
| Magnetic susceptibility | Material property/measurement | Geophysics/Geology | dimensionless or SI units |
| Magnetite | Mineral | Mineralogy/Geology | particle to crystal scale; Fe3O4 |
| Mica | Mineral group | Mineralogy/Geology | micrometers to centimeters |
| Microcline | Mineral (feldspar) | Mineralogy/Geology | millimeters to centimeters |
| Muscovite | Mineral (mica) | Mineralogy/Geology | micrometers to centimeters |
| Marble | Metamorphic rock | Petrology/Geology | centimeters to kilometers outcrops |
| Metamorphism | Geologic process | Petrology/Geology | temperature °C; pressure MPa to GPa |
| Metamorphic rock | Rock type | Geology | outcrop to regional scale |
| Metamorphic facies | Classification | Petrology/Geology | pressure-temperature fields |
| Metasomatism | Chemical alteration process | Petrology/Geology | local to regional; chemical fluxes |
| Metasedimentary rock | Rock type | Stratigraphy/Geology | outcrop scale |
| Meteorology | Discipline | Meteorology/Atmospheric science | hours to decades; local to global |
| Meteor | Atmospheric phenomenon | Planetary science/Meteorology | milliseconds to seconds; meters to kilometers |
| Meteoroid | Space object | Planetary science | micrometers to meters |
| Meteorite | Extraterrestrial rock | Planetary science/Geology | grams to tonnes; centimeter to meter |
| Mesosphere | Atmospheric layer | Atmospheric science | altitude ~50–85 km |
| Mesopause | Atmospheric boundary | Atmospheric science | altitude ~80–100 km |
| Mesoclimate | Scale of climate | Climatology/Meteorology | hectares to tens of km |
| Mesoscale | Scale classification | Meteorology/Oceanography | ~2–2,000 km; minutes to days |
| Mean sea level | Reference surface/measurement | Oceanography/Geodesy | meters; global average |
| Meander | River landform/process | Fluvial geomorphology | meters to kilometers wavelength |
| Mesa | Landform | Geomorphology | tens to hundreds of meters high |
| Mass wasting | Erosion process/hazard | Geomorphology/Geology | meters to kilometers; seconds to years |
| Mass balance | Measurement/process | Glaciology/Hydrology | meters water equivalent; years |
| Mass extinction | Biotic event | Paleontology/Geology | global; thousands to millions of years |
| Massif | Mountain block/landform | Tectonics/Geomorphology | kilometers; regional |
| Mass transport deposit | Sedimentary deposit | Marine geology/Geomorphology | meters to kilometers; local to regional |
| Mainshock | Seismic event | Seismology/Geology | magnitude scale (Mw); seconds to minutes |
| Megathrust earthquake | Hazard/earthquake type | Seismology/Tectonics | Mw typically >7; rupture hundreds of km |
| Megafan | Fluvial landform | Sedimentology/Geomorphology | tens to hundreds of kilometers across |
| Moraine | Glacial landform | Glaciology/Geomorphology | meters to kilometers |
| Mudflow | Mass-wasting/hazard | Geomorphology/Volcanology | meters to kilometers; minutes to hours |
| Mudstone | Sedimentary rock | Sedimentology/Geology | millimeters to kilometers outcrop |
| Mudrock | Sedimentary rock group | Sedimentology/Geology | outcrop scale |
| Mudflat | Coastal landform | Coastal geomorphology | meters to kilometers; intertidal zone |
| Mud volcano | Geologic feature | Geology/Geochemistry | meters to kilometers; small to large cones |
| Mylonite | Deformation rock | Structural geology | meters to kilometers; shear zones |
| Monocline | Fold type/structure | Structural geology | meters to kilometers wavelength |
| Monazite | Mineral | Mineralogy/Geology | micrometers to centimeters |
| Monzonite | Igneous rock | Petrology/Geology | outcrop scale; plutonic bodies |
| Monsoon | Climate phenomenon | Meteorology/Climatology | seasonal; months to half-year |
| Marine transgression | Sea-level/process | Stratigraphy/Geology | regional to global; thousands to millions years |
| Marine regression | Sea-level/process | Stratigraphy/Geology | regional to global; thousands to millions years |
| Marine terrace | Coastal landform | Coastal geomorphology | meters to hundreds of meters wide |
| Marginal sea | Ocean feature | Oceanography/Geography | hundreds to thousands of kilometers; regional |
| Mixed layer | Oceanic/atmospheric layer | Oceanography/Meteorology | meters to hundreds of meters; hours to months |
| Magnetostratigraphy | Dating/stratigraphic method | Stratigraphy/Geophysics | meters to kilometers; thousands to millions years |
| Mass concentration (mascon) | Gravity anomaly | Geophysics/Geodesy | microGals to mGal; regional |
| Magnitude | Measurement (earthquakes) | Seismology | moment magnitude (Mw); unitless scale |
| Mean annual temperature | Climatological metric | Climatology | °C or °F; annual average |
| Miocene | Geologic epoch | Stratigraphy/Paleontology | ~23.03–5.33 million years ago |
| Microclimate | Local climate | Climatology/Ecology | square meters to hectares; minutes to years |
| Moist adiabatic lapse rate | Thermodynamic rate | Meteorology | ~4–9 °C per km |
| Moisture | Hydrologic variable | Hydrology/Meteorology | percent, g/kg, mm of water |
| Mudcrack | Sedimentary structure | Sedimentology | centimeters to meters |
| Morainic (adjective) | Descriptive term | Glaciology/Geomorphology | feature-scale |
| Moisture content | Measurement | Soil science/Hydrology | percent by mass or volume |
| Marine sediment | Sediment type | Oceanography/Geology | millimeters to kilometers; grams to tonnes |
| Moraine-dammed lake | Glacial landform | Glaciology/Geomorphology | meters to kilometers; variable depth |
| Magmatic differentiation | Igneous process | Petrology | crystal sizes mm–cm; magma chamber scale |
| Magmatic stoping | Emplacement process | Igneous petrology | meters to kilometers |
| Meltwater | Hydrologic/cryospheric water | Hydrology/Glaciology | liters to cubic kilometers; seasonal |
| Mixture zone (ocean) | Oceanographic layer | Oceanography | meters to hundreds of meters |
| Mineral | Natural solid substance | Mineralogy/Geology | micrometers to meters |
| Mineralization | Ore-forming process | Economic geology/Geochemistry | meters to kilometers; local concentrations |
| Millennium-scale climate variability | Temporal climate concept | Climatology/Paleoclimatology | ~1,000 years |
| Mount | Landform (mountain) | Geomorphology/Tectonics | hundreds to thousands of meters elevation |
Descriptions
Magma
Molten silicate material beneath Earth’s surface that can cool to form igneous rock or erupt as lava.
Magma chamber
A large underground pocket where magma accumulates beneath a volcano, feeding eruptions and influencing volcanic behavior.
Magmatism
Processes that create and move magma, produce igneous rocks, and shape volcanic and plutonic features.
Mafic
Describes igneous rocks or minerals rich in magnesium and iron, typically darker and denser (e.g., basalt).
Maar
A shallow, broad volcanic crater formed by explosive interactions between magma and groundwater (common in phreatomagmatic eruptions).
Magmatic intrusion
An emplacement of magma into preexisting rock that cools to form intrusions like dikes and sills.
Mantle
Thick silicate layer between the crust and the core, driving convection, plate tectonics, and mantle melting.
Mantle plume
A rising column of hot mantle rock that can cause hotspots and large volcanic provinces.
Mantle convection
Slow circulation of mantle material driven by heat, which moves tectonic plates and redistributes Earth’s heat.
Magnetic field
The magnetic field generated by Earth’s core that protects the planet and guides compasses and migrating animals.
Magnetosphere
The region where Earth’s magnetic field dominates solar wind interaction, shaping radiation belts and aurora.
Magnetic anomaly
Local variations in Earth’s magnetic field caused by differing rock types, useful for mapping subsurface geology.
Magnetic declination
The angle between geographic north and magnetic north at a location, important for compass navigation.
Magnetic inclination
Angle between Earth’s magnetic field and the horizontal plane; varies with latitude and used in paleomagnetism.
Magnetic reversal
When Earth’s magnetic field flips polarity, recorded in rocks and used to date tectonic and volcanic events.
Magnetic susceptibility
A measure of how much a rock or mineral becomes magnetized in an external magnetic field; aids mineral exploration.
Magnetite
An iron oxide mineral that is strongly magnetic and common in igneous and metamorphic rocks.
Mica
A group of sheet silicate minerals (e.g., biotite, muscovite) known for perfect basal cleavage and shiny flakes.
Microcline
A potassium feldspar mineral common in granites and metamorphic rocks, often showing grid-like twinning.
Muscovite
A light-colored mica common in metamorphic and igneous rocks, used as an electrical insulator and indicator of metamorphism.
Marble
A metamorphosed limestone or dolostone with recrystallized calcite, used in sculpture and building stone.
Metamorphism
Alteration of rocks by heat, pressure, and fluids that produces metamorphic textures and minerals.
Metamorphic rock
Rock transformed from a preexisting rock by heat, pressure, or chemically active fluids, like schist or gneiss.
Metamorphic facies
Groups of mineral assemblages that indicate the pressure-temperature conditions during metamorphism.
Metasomatism
The chemical alteration of a rock by fluids that introduce or remove elements and change mineralogy.
Metasedimentary rock
A sedimentary rock that has undergone metamorphism but retains sedimentary features like bedding or fossils.
Meteorology
The scientific study of the atmosphere and weather processes, including forecasting and climate dynamics.
Meteor
A streak of light produced when a meteoroid burns up entering Earth’s atmosphere (a “shooting star”).
Meteoroid
A small rock or particle in space that can become a meteor if it enters Earth’s atmosphere.
Meteorite
A fragment of rock or metal from space that survives passage through the atmosphere and lands on Earth’s surface.
Mesosphere
The atmospheric layer above the stratosphere where temperatures fall with height and meteors often burn up.
Mesopause
The temperature minimum layer that separates the mesosphere from the thermosphere, often the coldest point in Earth’s atmosphere.
Mesoclimate
Local climate conditions intermediate between microclimate and regional climate, influenced by terrain and land cover.
Mesoscale
A spatial scale in atmospheric and ocean sciences covering phenomena like thunderstorms, sea breezes, and mesoscale eddies.
Mean sea level
The average sea surface height used as a vertical datum for elevations and tidal studies.
Meander
A sinuous bend or curve in a river formed by erosion and deposition, common in low-gradient channels.
Mesa
A flat-topped, steep-sided hill or plateau formed by erosion of layered rocks, common in arid regions.
Mass wasting
Downslope movement of soil and rock under gravity, including landslides, flows, and slumps.
Mass balance
Net gain or loss of mass (snow, ice, water) for a glacier, ice sheet, or watershed over time.
Mass extinction
A relatively rapid, widespread loss of a large proportion of Earth’s species, often linked to environmental change.
Massif
A compact group of connected mountains or a topographically high crustal block formed by uplift and faulting.
Mass transport deposit
Large deposits created by submarine landslides or slumps that transport sediment downslope.
Mainshock
The largest earthquake in a sequence, often followed by aftershocks.
Megathrust earthquake
Large earthquakes that occur at subduction zone thrust faults and often produce tsunamis.
Megafan
A very large alluvial fan deposited by rivers where gradient suddenly decreases, common near mountain fronts.
Moraine
An accumulation of glacially transported debris (till) deposited at glacier margins, forming ridges or hummocky terrain.
Mudflow
Rapid flow of water-saturated sediment (often from heavy rain or melting), capable of moving large debris and causing damage.
Mudstone
A fine-grained sedimentary rock composed largely of clay- and silt-sized particles, common in low-energy environments.
Mudrock
A broad term for fine-grained sedimentary rocks including mudstone, shale, and siltstone.
Mudflat
Flat, muddy areas exposed at low tide and inundated at high tide, rich in organic matter and habitats.
Mud volcano
A surface expression where mud and gas erupt slowly, often in petroleum-bearing basins or subduction zones.
Mylonite
A fine-grained, foliated rock formed by intense ductile shear in fault zones.
Monocline
A steep, step-like fold in rock layers that creates a local change in dip between relatively horizontal strata.
Monazite
A rare-earth phosphate mineral used for dating rocks and as an indicator of metamorphic conditions.
Monzonite
A coarse-grained intrusive igneous rock with roughly equal plagioclase and orthoclase feldspar.
Monsoon
A seasonal reversal of winds that brings distinct wet and dry seasons, especially pronounced in South and Southeast Asia.
Marine transgression
Advance of the sea over land that causes shoreline and sedimentary environments to shift landward.
Marine regression
Retreat of the sea from the land, exposing former seabeds and shifting depositional environments seaward.
Marine terrace
Flat, wave-cut platforms uplifted above current sea level, recording past sea levels and tectonic uplift.
Marginal sea
A semi-enclosed sea near a continent, like the North Sea or Mediterranean, with distinct circulation and ecology.
Mixed layer
The upper layer of the ocean or atmosphere well mixed by turbulence, controlling heat and gas exchange.
Magnetostratigraphy
Correlation and dating of rock sequences using recorded magnetic polarity reversals.
Mass concentration (mascon)
A localized high in gravitational acceleration caused by dense subsurface mass, commonly observed on planetary bodies.
Magnitude
A numeric measure of earthquake size based on energy release; commonly reported as the moment magnitude.
Mean annual temperature
The average temperature at a location computed over a year, used to characterize climate.
Miocene
A division of the Neogene Period marked by significant climate change and mammal evolution.
Microclimate
Climate conditions in a small, specific area that can differ markedly from the surrounding regional climate.
Moist adiabatic lapse rate
The rate at which saturated (moist) air cools as it rises, variable with temperature and moisture content.
Moisture
Amount of water vapor or liquid water present in air, soil, or materials; central to weather and hydrology.
Mudcrack
Polygonal cracks that form in drying mud or clay, preserved in the rock record as indicators of exposure and desiccation.
Morainic (adjective)
Relating to or formed by moraines or glacial deposition; used to describe landforms and sediments deposited by glaciers.
Moisture content
The amount of water contained in soil, sediment, or rock, important for plant growth and slope stability.
Marine sediment
Particles deposited on the ocean floor from biological, chemical, or terrigenous sources that record environmental history.
Moraine-dammed lake
A lake formed when moraines act as natural dams, common at the margins of retreating glaciers.
Magmatic differentiation
Separation of minerals from melt during cooling, producing different igneous rock types from one magma.
Magmatic stoping
A process where ascending magma breaks off and incorporates blocks of surrounding rock into an intrusion.
Meltwater
Water released from melting snow or ice that influences river flow, erosion, and glacier dynamics.
Mixture zone (ocean)
A zone where different water masses mix, affecting temperature, salinity, and nutrient distributions.
Mineral
A naturally occurring, inorganic solid with a definite chemical composition and crystal structure.
Mineralization
The process that forms mineral deposits, concentrating economically important metals in rock.
Millennium-scale climate variability
Long-term climate fluctuations occurring on roughly thousand-year timescales, seen in paleoclimate records.
Mount
A large natural elevation of Earth’s surface rising prominently above its surroundings, formed by tectonic or volcanic activity.