Earth System

The interacting parts of Earth, including the geosphere, hydrosphere, atmosphere, and biosphere.

Geosphere

The solid Earth, including the crust, mantle, and core.

Crust

The thin, outermost compositional layer of Earth.

Mantle

The thick layer between the crust and core, made mostly of silicate rock rich in iron and magnesium.

Core

The innermost layer of Earth, composed mostly of iron and nickel.

Lithosphere

The rigid outer layer consisting of the crust and uppermost mantle; divided into tectonic plates.

Asthenosphere

A weaker, hotter, ductile part of the upper mantle beneath the lithosphere that allows plates to move.

Continental Crust

Thicker and generally less dense crust that makes up the continents.

Oceanic Crust

Thinner and denser crust that makes up the ocean floor.

P Wave

A compressional seismic wave that can travel through solids and liquids.

S Wave

A shear seismic wave that travels through solids but cannot travel through liquids.

How do we know the outer core is liquid?

S waves cannot travel through the liquid outer core, creating an S-wave shadow zone.

How do seismic waves help us study Earth's interior?

Their speed and direction change when they pass through materials with different properties.

Coring

Drilling into Earth to obtain rock samples directly from shallow depths.

Xenolith

A piece of rock from deeper Earth that is carried upward by magma.

Ophiolite

A section of oceanic crust and upper mantle exposed on land.

Meteorites

Rocks from space that provide evidence about the materials that formed Earth and the solar system.

Continental Drift

The idea that continents have moved to different positions over geologic time.

Alfred Wegener

The scientist who proposed the theory of continental drift.

Evidence for Continental Drift

Matching coastlines, matching fossils, matching rock formations, and evidence of past climates.

Problem with Wegener's Continental Drift

Wegener could not provide a convincing mechanism or driving force for continental movement.

Plate Tectonics

The theory that Earth's lithosphere is divided into moving plates.

Divergent Boundary

A boundary where two plates move apart and new crust forms.

Convergent Boundary

A boundary where two plates move toward each other.

Transform Boundary

A boundary where two plates slide horizontally past each other.

Mid-Ocean Ridge

A long underwater mountain chain formed where oceanic plates diverge and new crust forms.

Rift Valley

A depression formed where continental crust is being pulled apart.

Oceanic-Continental Convergence

Oceanic crust subducts beneath continental crust, forming a trench, volcanoes, and mountains.

Oceanic-Oceanic Convergence

One oceanic plate subducts beneath another, forming a trench and volcanic island arc.

Continental-Continental Convergence

Two continents collide, producing large mountain ranges.

Transform Boundary Landforms

Fault zones and earthquakes are common where plates slide past each other.

Subduction

The process where one tectonic plate sinks beneath another into the mantle.

Evidence for Subduction

Deep earthquakes and volcanoes occur along subduction zones.

Seafloor Spreading

The process where new oceanic crust forms at mid-ocean ridges and moves outward.

Magnetic Anomalies

Alternating bands of normal and reversed magnetic polarity preserved in oceanic crust.

Why do magnetic anomalies prove seafloor spreading?

Symmetrical magnetic stripes on both sides of ridges show that new crust formed and moved outward.

Ocean-Floor Age Evidence

The youngest oceanic crust is at mid-ocean ridges and becomes older farther from the ridge.

Ocean-Floor Sediment Evidence

Sediment is thinnest near ridges and becomes thicker farther from them.

Ocean-Floor Temperature Evidence

New crust near ridges is hotter; older crust farther away is cooler.

Determining Plate Direction

Plate direction can be determined using magnetic stripes, hotspot tracks, and other geological features.

Determining Plate Speed

Plate speed can be calculated by dividing distance traveled by the amount of time.

Ridge Push

Gravity-driven force that pushes plates away from elevated mid-ocean ridges.

Slab Pull

The force produced when dense oceanic lithosphere sinks at a subduction zone and pulls the plate with it.

Suction/Rollover

Mantle flow associated with subduction that helps move the descending plate.

Wilson Cycle

The repeating cycle of continental rifting, ocean-basin opening, ocean-basin closing, and continental collision.

Wilson Cycle: Rifting

Continental crust begins pulling apart and a rift valley can form.

Wilson Cycle: Ocean Opening

Seafloor spreading creates new oceanic crust and an ocean basin grows.

Wilson Cycle: Subduction

Old oceanic lithosphere begins sinking into the mantle, causing the ocean basin to shrink.

Wilson Cycle: Continental Collision

Continents collide after the ocean closes, forming mountains.

Wilson Cycle Periodicity

The Wilson Cycle repeats over hundreds of millions of years.

Mineral

A naturally occurring, inorganic solid with an ordered atomic structure and a specific chemical composition.

Chemical Bonds

Forces that hold atoms together in minerals.

Ionic Bond

An attraction between positively and negatively charged ions.

Covalent Bond

A bond formed when atoms share electrons.

Luster

The way a mineral reflects light from its surface.

Streak

The color of a mineral in powdered form.

Hardness

A mineral's resistance to being scratched.

Specific Gravity

A mineral's density compared with the density of water.

Cleavage

A mineral's tendency to break along specific planes of weakness.

Fracture

A mineral's tendency to break irregularly rather than along cleavage planes.

Crystalline Structure

The orderly, repeating arrangement of atoms in a mineral.

Color

A visible mineral property, but often less reliable for identification because impurities can change it.

Silicates

Minerals containing silicon and oxygen; they make up most of Earth's crust.

Carbonates

Minerals containing a carbonate ion combined with other elements.

Sulfides

Minerals containing sulfur combined with a metal.

Oxides

Minerals containing oxygen combined with another element.

Sulfates

Minerals containing a sulfate ion.

Halides

Minerals containing halogen elements such as chlorine or fluorine.

Most Common Elements in Earth's Crust

Oxygen and silicon are the two most abundant elements, followed by aluminum and iron.

Igneous Rock

Rock formed when molten rock cools and crystallizes.

Magma

Molten rock beneath Earth's surface.

Lava

Molten rock that reaches Earth's surface.

Intrusive Igneous Rock

Igneous rock that crystallizes below Earth's surface.

Extrusive Igneous Rock

Igneous rock that forms when lava cools at Earth's surface.

Intrusive vs. Extrusive

Intrusive rocks cool slowly underground; extrusive rocks cool rapidly at the surface.

Felsic

High-silica composition; generally lighter colored and more viscous.

Intermediate

Composition between felsic and mafic.

Mafic

Lower-silica composition rich in iron and magnesium; generally darker and less viscous.

Ultramafic

Very low-silica composition with abundant magnesium and iron.

Silica and Viscosity

More silica generally produces higher magma viscosity.

High-Viscosity Magma

Thick magma that resists flowing and can trap gases.

Low-Viscosity Magma

Runny magma that allows gases to escape more easily.

Magma at Mid-Ocean Ridges

Forms mainly by decompression melting of hot mantle as it rises.

Magma at Hotspots

Forms from melting associated with unusually hot mantle rising toward the surface.

Magma at Subduction Zones

Water released from the subducting slab lowers the melting temperature of mantle rock.

Effect of Pressure on Melting

Decreasing pressure can cause hot mantle rock to melt without adding heat.

Effect of Water on Melting

Water lowers the melting temperature of mantle rock.

Bowen's Reaction Series

Shows the sequence in which different minerals crystallize as magma cools.

Fractional Crystallization

Early-forming crystals are removed from magma, changing the composition of the remaining melt.

Why does fractional crystallization produce different rocks?

Removing certain minerals changes the remaining magma's composition, producing different igneous rocks.

Dike

An igneous intrusion that cuts across existing rock layers.

Sill

An igneous intrusion that forms parallel to existing rock layers.

Oceanic Lithosphere Composition

From bottom to top: peridotite, gabbro, and basalt.

Peridotite

An ultramafic rock that makes up much of the upper mantle beneath oceanic crust.

Gabbro

A coarse-grained mafic rock forming part of the lower oceanic crust.

Basalt

A fine-grained mafic rock forming the upper oceanic crust.

Volcano

A vent or landform through which magma, lava, ash, and gases reach Earth's surface.

Shield Volcano

A broad, gently sloping volcano built mainly from low-viscosity basaltic lava.

Composite Volcano

A steep volcano built from alternating lava flows and pyroclastic material.

Cinder Cone

A relatively small, steep volcano made mostly of loose volcanic fragments.

Explosive Volcanic Eruption

An eruption favored by high-viscosity magma that traps gases.

Metamorphism

The alteration of existing rock by heat, pressure, and/or chemically active fluids without melting it completely.

Regional Metamorphism

Large-scale metamorphism caused mainly by heat and pressure during mountain building and plate convergence.

Contact Metamorphism

Localized metamorphism caused mainly by heat from nearby magma.

Metamorphism at Subduction Zones

Subduction creates high-pressure conditions and can produce metamorphic rocks.

Deformation

The change in the shape, position, or volume of rock caused by stress.

Stress

A force applied to rock that can cause deformation.

Compression

Stress that squeezes rocks together.

Tension

Stress that pulls rocks apart.

Shear

Stress that causes rocks to slide past one another.

Fold

A bend in originally layered rock caused by deformation.

Anticline

An upward-arching fold with the oldest rocks toward the center.

Syncline

A downward-curving fold with the youngest rocks toward the center.

Syncline Rock Ages

Rocks become younger toward the center of a syncline.

Anticline Rock Ages

Rocks become older toward the center of an anticline.

Fault

A fracture in Earth's crust along which rocks have moved.

Normal Fault

A fault caused by tension where the hanging wall moves downward.

Reverse Fault

A fault caused by compression where the hanging wall moves upward.

Thrust Fault

A low-angle reverse fault caused by compression.

Strike-Slip Fault

A fault where rocks move mainly horizontally past one another.

Compressional Faults

Reverse and thrust faults are associated with compression.

Normal Fault Stress

Normal faults are associated with tension.

Earthquake

A sudden release of stored energy caused by movement along a fault.

Focus

The point inside Earth where an earthquake begins.

Epicenter

The point on Earth's surface directly above the earthquake's focus.

Earthquake Evidence for Subduction

Deep earthquakes form along descending slabs, tracing subducting plates into the mantle.

Outer Core

The liquid layer between the mantle and inner core, composed mostly of iron and nickel.

Inner Core

The solid, extremely dense, iron-rich center of Earth.

Why is the inner core solid?

Extreme pressure keeps the inner core solid despite its very high temperature.

How do we know what Earth's core contains?

Seismic evidence, meteorites, and laboratory experiments provide clues about its composition.

How do we study Earth's deep interior?

Seismic waves, meteorites, xenoliths, ophiolites, drilling, and laboratory experiments provide evidence.

Rock vs. Mineral

A mineral is a naturally occurring solid with a specific composition; a rock is an aggregate of minerals or other materials.

Weathering vs. Erosion

Weathering breaks down rock; erosion transports weathered material.

Felsic vs. Mafic

Felsic is higher in silica; mafic is lower in silica and richer in iron and magnesium.

Sill vs. Dike

A sill runs parallel to rock layers; a dike cuts across them.

Contact vs. Regional Metamorphism

Contact is localized near magma; regional affects large areas during tectonic activity.

Syncline vs. Anticline

Syncline bends downward with younger rocks in the center; anticline arches upward with older rocks in the center.

Normal vs. Reverse Fault

Normal faults have the hanging wall move down; reverse faults have it move up.

Compression vs. Tension

Compression squeezes rocks together; tension pulls rocks apart.

Which fault is compressional?

Reverse and thrust faults are caused by compression.

Which fault is associated with tension?

Normal faults are caused by tension.