EARTH-SCIENCE MIDTERMS

Geosphere

The solid part of Earth, including the crust, mantle, and core; encompasses rocks, soils, landforms, and the processes that shape Earth’s surface.

Biosphere

All living organisms on Earth; interacts with the atmosphere, hydrosphere, geosphere, and cryosphere; includes humans.

Hydrosphere

All water on Earth (oceans, rivers, lakes, groundwater, glaciers) existing in liquid, solid, or gaseous forms.

Atmosphere

The gaseous envelope around Earth, about 500 km thick, composed mainly of nitrogen and oxygen; protects living things and regulates climate.

Cryosphere

Portion of Earth where water is frozen—ice sheets, glaciers, snow—affecting landscapes and freshwater availability.

Plate Tectonics

Theory that Earth’s lithospheric plates move slowly, reshaping continents, mountains, earthquakes, and volcanoes.

Mohorovicic Discontinuity (Moho)

The boundary between the crust and mantle where seismic velocities increase.

Crust

Outermost Earth layer, divided into continental and oceanic crust; varies in thickness and composition.

Continental Crust

Thicker, less dense crust made mostly of granitic rocks; roughly 30–50 km thick (up to 70 km in mountains).

Oceanic Crust

Thinner, more dense crust made primarily of basalt; about 5–10 km thick.

Mantle

Layer beneath the crust, divided into upper mantle, transition zone, and lower mantle; extends to about 2900 km.

Asthenosphere

Part of the upper mantle that can flow slowly, enabling plate movement.

Upper Mantle

Section from the Moho to about 660 km depth; includes rigid rocks and the asthenosphere.

Transition Zone

Region between ~410–660 km depth where mineral structure changes under pressure.

Lower Mantle

Hot, solid rock layer from ~660 km to ~2900 km depth; moves slowly over geological time.

Outer Core

Liquid iron–nickel layer from ~2900 to ~5150 km depth; generates Earth’s magnetic field via geodynamo.

Inner Core

Solid sphere of iron–nickel at Earth's center, about 5150–6371 km radius; extremely hot but solid due to immense pressure.

Geodynamo

Convection of liquid iron in the outer core that creates Earth’s magnetic field.

Water Cycle

Continuous movement of water among the hydrosphere and atmosphere via evaporation, condensation, precipitation, and collection.

Evaporation

Process by which liquid water is transformed into water vapor and rises into the atmosphere.

Condensation

Process by which water vapor cools and forms tiny droplets, creating clouds.

Precipitation

Rain, snow, sleet, or hail that falls to Earth from clouds.

Collection

Water gathering in bodies or seeping into the ground, restarting the cycle.

Exosphere

Outermost layer of the atmosphere where most satellites orbit; transition to space.

Thermosphere

Layer above the mesosphere; can reach very high temperatures and responds to solar radiation.

Mesosphere

Middle layer where most meteors burn up due to friction with gases.

Stratosphere

Layer above the troposphere; contains the ozone layer and warms with altitude.

Troposphere

Lowest atmospheric layer; contains most weather and water vapor; where everyday life occurs.

Ozone

O3 molecule concentrated in the stratosphere that absorbs UV radiation.

Ozone Layer

Region of high ozone in the stratosphere that shields Earth from UV radiation.

Nitrogen

About 78% of Earth's atmosphere; stabilizes atmospheric pressure.

Oxygen

About 21% of the atmosphere; essential for respiration and combustion.

Water Vapor

Gaseous water in the atmosphere; varies from 0–4% and drives greenhouse effect and weather.

Greenhouse Gases

Gases such as CO2 and methane that trap heat in the atmosphere, influencing climate.

Ozone Depletion

Reduction of ozone in the stratosphere caused by pollutants like CFCs; recovering due to international agreements.

Montreal Protocol

International treaty to phase out ozone-depleting substances to protect the ozone layer.

Weather

Short-term atmospheric conditions in a region (temperature, humidity, wind, precipitation).

Climate

Long-term average of weather patterns in a region over decades.

Soil

Part of the geosphere that provides nutrients and a medium for plant growth; supports habitats.

Erosion

Wearing away of rocks and soils by wind, water, or ice, shaping landforms.

Ecosystem

A community of organisms and their physical environment interacting as a system.

Mineral Resource

A concentration or occurrence of solid material of economic interest in the Earth's crust in such form, grade, or quality and quantity that there are reasonable prospects for eventual economic extraction.

Metallic mineral deposits

Deposits containing metals such as gold, silver, copper, platinum, and iron.

Nonmetallic resources

Minerals like talc, fluorite, sulfur, sand, and gravel.

Magmatic ore deposits

Concentrations formed in an igneous body through magmatic processes (crystal fractionation, partial melting, crystal settling).

Hydrothermal ore deposits

Concentrations produced by hot aqueous fluids moving through fractures and pore spaces in rocks, often derived from magma crystallization or heated groundwater.

Vein deposits

A fairly well-defined, usually narrow zone of mineralization that occurs in faults, fissures, or shear zones.

Disseminated ore deposits

Ore minerals distributed as minute masses through large volumes of rock; common in porphyry copper deposits.

Massive sulfide deposit

Precipitation of sulfide minerals (e.g., sphalerite, chalcopyrite) from hot fluids at oceanic spreading centers when they meet cold groundwater or seawater.

Sedimentary ore deposits

Concentrations formed by chemical precipitation from lakes or seawater in sedimentary environments.

Placer ore deposits

Concentrations formed by gravity separation during sedimentary processes, often aided by flowing surface water; common for gold, platinum, diamonds, tin.

Residual ore deposits

Deposits formed by chemical weathering and leaching, with reduced rock volume; formation depends on climate, relief, and parent rock.

Ore deposit

A mineral deposit that has been tested and is known to be economically profitable to mine.

Ore

Naturally occurring material from which a mineral or minerals of economic value can be extracted.

Mineral occurrence

Concentration of a mineral of scientific or technical interest.

Mineral deposit

A mineral occurrence large enough in size/grade to enable extraction under favorable conditions.

Aggregate

Rock or mineral material used as filler in cement, asphalt, plaster, etc.; describes nonmetallic deposits.

Surface mining

Mining near the surface; typically more cost-effective than underground mining; suitable for near-surface minerals.

Underground mining

Mining for minerals located deep beneath the surface; commonly used for minerals like gold, lead, and silver.

Copper

Indispensable metal used in electrical wiring, with antimicrobial properties, and used in coins.

Platinum

Metal used in circuit sheets, electrical devices, fiber optics, pacemakers.

Iron ore

Iron-containing material essential for steel production and infrastructure (rails, etc.).

Silver

Precious metal used in jewelry and flatware; highly conductive and resistant to corrosion.

Gold

Valued metal used in jewelry, currency, and high-value artifacts; also a store of wealth.

Cobalt

Magnetic metal alloyed with aluminum and nickel to make strong magnets.

Bauxite

Ore used to produce aluminum; a mixture of minerals.

Lithium

Soft metal used in alloys and especially in batteries for electronics and electric vehicles.

Zinc

Metal important for corrosion protection; used in batteries, roofing, die casting, and health-related applications.

Potash

Primarily used as fertilizer (potassium); remainder used for various chemicals.

Endogenic ore formation

Ore accumulation through internal geologic activity, such as magma moving ore toward the surface.

Rock

A naturally occurring solid that forms by Earth's natural processes; typically composed of minerals or mineral-like material.

Mineral

A naturally occurring, inorganic solid with a definite chemical composition and an orderly internal crystal structure.

Naturally occurring

Formed by natural processes rather than by human intervention.

Inorganic

Not formed by or derived from living matter; minerals are inorganic.

Crystal structure

The orderly, repeating arrangement of atoms in a mineral’s solid form.

Chemical formula

A symbolic way to express the ratio of elements in a mineral (e.g., NaCl for halite, SiO2 for quartz).

Mohs hardness scale

Standard scale (1-10) ranking minerals by their resistance to scratching.

Igneous rock

Rock formed from the cooling and solidification of molten magma or lava.

Extrusive rock

Igneous rock that forms when magma erupts at the surface as lava and cools quickly, producing very fine crystals.

Intrusive rock

Igneous rock that cools slowly beneath the surface, forming large crystals.

Aphanitic

Fine-grained texture of igneous rocks, with crystals too small to see, due to rapid cooling.

Phaneritic

Coarse-grained texture of igneous rocks, with visible crystals from slow cooling underground.

Porphyritic

Texture with large crystals (phenocrysts) embedded in a finer-grained matrix.

Glassy

Texture resembling glass, formed when lava quenches rapidly and crystallization is minimal.

Pyroclastic

Rock composed of ejected volcanic fragments and ash.

Ultramafic

Igneous rocks with very dark color and high magnesium and iron content.

Mafic

Dark-colored igneous rocks rich in magnesium and iron.

Intermediate

Igneous composition between mafic and felsic.

Felsic

Light-colored igneous rocks rich in silica and feldspar/mineral silicates.

Granite

A common felsic intrusive igneous rock used in building and countertops.

Pumice

A highly vesicular, light-colored extrusive rock used as an abrasive.

Sedimentary rock

Rock formed by the compaction and cementation of sediments derived from erosion and weathering.

Erosion

Wearing away and transportation of rocks by wind, water, or ice.

Deposition

Laying down of sediment carried by wind, water, or ice.

Compaction

Compression of sediments under their own weight before cementation.

Cementation

Process by which sediments are glued together by mineral precipitation.

Conglomerate

Sedimentary rock composed of rounded gravel-sized clasts.

Breccia

Sedimentary rock with angular fragments held together by a matrix.

Shale

Soft, fine-grained sedimentary rock formed from clay/silt.

Red sandstone

Sandstone colored red due to iron oxides.