04 Geology and Earth Resources

A dynamic planet that continually changes in structure.

Earth

The dense, extremely hot metallic interior of Earth, mostly iron; solid at the center but fluid in the outer part, generating the magnetic field.

Core

The hot, pliable rocky layer surrounding the outer core; contains lighter elements such as oxygen, silicon, and magnesium.

Mantle

The cool, brittle outer layer of rock; thin and dense under oceans, thick and light under continents.

Crust

The rigid outer layer consisting of the crust and upper mantle; brittle and elastic in nature.

Lithosphere

The weak, plastic zone beneath the lithosphere that allows tectonic plates to move.

Asthenosphere

The theory describing large-scale movements and deformation of Earth’s lithospheric plates.

Plate Tectonics

Wegener’s hypothesis that continents once formed a single supercontinent (Pangaea) and later separated.

Continental Drift

A prehistoric supercontinent meaning “all lands” that eventually split into the modern continents.

Pangaea

The creation of new oceanic crust at mid-ocean ridges as plates diverge.

Seafloor Spreading

Region where the lithosphere is being stretched and split apart, often forming new ocean basins.

Rift Zone

Location where three tectonic plates meet, such as the Afar Depression in Ethiopia.

Triple Junction

Region where one plate descends beneath another into the mantle, consuming oceanic crust.

Subduction Zone

A curved chain of volcanic islands formed at an ocean–ocean convergent boundary.

Island Arc

Uplift and deformation of Earth’s crust due to collision and convergence of plates.

Mountain Building

Fracture where two lithospheric plates slide horizontally past each other (e.g., San Andreas Fault).

Transform Fault

Plate boundary where plates move apart and new crust forms from rising magma.

Divergent Boundary

Plate boundary where plates move toward one another, forming mountains or trenches.

Convergent Boundary

A naturally occurring, inorganic, solid substance with definite chemical composition and crystalline structure.

Mineral

The most abundant mineral group composed of silicon and oxygen, often with other elements.

Silicates

A hard, weathering-resistant silicate of silicon and oxygen; used in glassmaking and construction.

Quartz

The most common minerals in the crust, composed of silicon, oxygen, aluminum, and alkali metals.

Feldspars

Dark-colored silicates containing iron and/or magnesium, such as olivine.

Ferromagnesian Minerals

Silicate minerals with sheet-like crystal structures that split easily into thin layers.

Micas

Sheet silicate minerals that can absorb or lose water; used in ceramics, construction, and drilling fluids.

Clays

Minerals grouped by common negative ions such as carbonates, sulfates, and halides.

Nonsilicates

A solid aggregate of one or more minerals or mineral materials bound together.

Rock

Rock formed by the cooling and solidification of molten magma.

Igneous Rock

Coarse-grained igneous rock formed slowly beneath Earth’s surface (e.g., granite).

Plutonic Rock

Fine-grained igneous rock formed from lava cooling quickly at or near the surface (e.g., basalt, obsidian).

Volcanic Rock

Natural volcanic glass produced by rapid cooling of lava without crystal formation.

Obsidian

Igneous rock containing large crystals (phenocrysts) in a fine-grained matrix.

Porphyry

Unconsolidated material transported and deposited by wind, water, ice, or gravity.

Sediment

Rock formed from compacted and cemented sediments near the Earth’s surface.

Sedimentary Rock

Rock composed of fragments of preexisting rocks, such as sandstone or shale.

Clastic Sedimentary Rock

Rock formed from precipitation of minerals out of solution, such as limestone.

Chemical Sedimentary Rock

Carbon-rich remains of living organisms that form materials such as coal.

Organic Sediment

Rock formed when preexisting rock is changed by heat, pressure, or chemical processes.

Metamorphic Rock

Alteration of rock caused by heat from nearby magma intrusions.

Contact Metamorphism

Widespread metamorphism resulting from high pressure and temperature during mountain building.

Regional Metamorphism

Layered texture in metamorphic rocks resulting from alignment of platy minerals.

Foliation

Fine-grained metamorphic rock derived from shale that splits easily into flat slabs.

Slate

Medium- to coarse-grained metamorphic rock rich in mica or similar minerals.

Schist

Banded metamorphic rock with alternating light and dark mineral layers.

Gneiss

Hard metamorphic rock formed from quartz-rich sandstone.

Quartzite

Metamorphic rock formed when limestone recrystallizes under heat and pressure.

Marble

Metamorphic rock dominated by amphibole minerals; indicates moderate metamorphism.

Amphibolite

The continuous process by which rocks of any type are transformed into other types through geological processes.

Rock Cycle

Study of minerals and rocks valuable for manufacturing and commerce.

Economic Mineralogy

Elements such as iron, aluminum, copper, and manganese essential for industrial use.

Metals

Mineral resources such as sand, gravel, limestone, salts, and soils.

Nonmetals

Recovery of valuable minerals from stream sediments by washing and separation.

Placer Mining

Extraction of ores from beneath the surface through tunnels and shafts.

Underground Mining

Surface mining method that removes large volumes of overburden to expose ore.

Open-pit Mining

Coal mining method that removes ridge tops, depositing waste in valleys.

Mountaintop Removal

Heating ore to extract metals; often produces significant air pollution.

Smelting

Process of dissolving metals from low-grade ore using chemical solutions like cyanide.

Heap-Leach Extraction

Effort to preserve mineral resources and minimize mining impacts.

Conservation of Geological Resources

Reuse of metals and materials to conserve energy and reduce waste.

Recycling

Small-scale steel plants that recycle scrap metal efficiently and at lower energy cost.

Minimills

Alternatives such as polymers, ceramics, and fiber optics replacing traditional metals.

New Materials

Sudden release of energy along faults causing ground movement.

Earthquake

Large sea wave generated by underwater earthquakes or landslides.

Tsunami

Opening in Earth’s crust through which magma, gases, and ash erupt.

Volcano

Rapid downslope movement of soil or rock due to gravity.

Landslide

Collective term for downslope movements of rock and soil under gravity.

Mass Wasting

Overflow of water onto normally dry land, often in river floodplains.

Flood

Natural redistribution of sand and sediments by wave motion.

Beach Erosion

Short-term local atmospheric conditions such as rain, snow, wind, or storms.

Weather

Long-term average of temperature, humidity, and precipitation patterns.

Climate

Warming of Earth caused by atmospheric gases trapping heat radiating from the surface.

Greenhouse Effect

Heat-trapping gases including water vapor, carbon dioxide, methane, nitrous oxide, and chlorofluorocarbons.

Greenhouse Gases

Long-term increase in Earth’s average surface temperature mainly due to fossil fuel combustion.

Global Warming

Long-term alteration of global or regional climate systems driven by human and natural factors.

Climate Change