Earth Science Tri A Exam Review

Vocabulary study cards covering Earth's internal structure, plate tectonics, volcanoes, earthquakes, and astronomy based on the Tri A Earth Science exam review sheet.

Crust

The thin, solid, rocky outermost layer of Earth; oceanic crust is generally basaltic, while continental crust is generally granitic.

Mantle

A very thick layer of hot silicate rock beneath the crust that is mostly solid but can slowly deform and flow over long periods.

Upper mantle

The upper portion of the mantle that includes both the rigid mantle section of the lithosphere and the softer asthenosphere beneath it.

Lower mantle

The deeper, hotter, higher-pressure region of the mantle composed of solid rock that slowly flows over geologic time.

Outer core

A layer of liquid iron and nickel whose motion helps generate Earth's magnetic field.

Inner core

A solid iron-nickel sphere at Earth's center that remains solid due to immense pressure.

Lithosphere

The rigid outer shell of Earth consisting of the crust plus the uppermost rigid mantle; it is broken into tectonic plates.

Asthenosphere

The hot, weak, and ductile part of the upper mantle directly beneath the lithosphere that can slowly flow, allowing plates to move over it.

Density

Mass divided by volume ($D = m \div V$); a denser tectonic plate is more likely to sink during subduction.

Convection currents

Slow circulation in the mantle driven by heat differences, where hotter, less-dense material rises and cooler, denser material sinks.

Radioactive decay

A process where an unstable atomic nucleus changes into a more stable form and releases energy and particles, contributing to Earth's internal heat.

Wilson Cycle

The long-term cycle of opening, widening, closing, and eventual re-forming of ocean basins as continents split and collide.

Convergent boundary

A plate boundary where plates move toward each other, causing collision, subduction, trenches, volcanic arcs, mountain building, and earthquakes.

Divergent boundary

A plate boundary where plates move away from each other, allowing magma to rise and form new crust at mid-ocean ridges or continental rift valleys.

Transform boundary

A plate boundary where plates slide horizontally past each other along faults, producing earthquakes without creating or destroying crust.

Trench

A long, deep depression in the seafloor formed where one plate subducts beneath another at a convergent boundary.

Seafloor spreading

The process at divergent ocean boundaries where tectonic plates pull apart, allowing mantle material to rise and cool into new oceanic crust.

Passive margin

A continental border, such as the east coast of the United States, that is not currently situated next to a major active plate boundary.

Active margin

A continental border near active plate boundaries, such as much of the U.S. west coast, where faults, earthquakes, and volcanoes are common.

Magma

Molten rock located beneath Earth's surface.

Lava

Molten rock that has reached Earth's surface.

Shield volcano

A broad, gently sloping volcano built mostly from fluid, low-viscosity basaltic lava that travels long distances.

Composite volcano (stratovolcano)

A steep-sided volcano constructed from alternating layers of lava and fragmented material, often producing explosive eruptions from viscous, gas-rich magma.

Basaltic lava

Lava with relatively low silica content and lower viscosity, allowing it to flow more easily.

Rhyolitic lava

Lava with high silica content and high viscosity that flows slowly, traps gas, and frequently contributes to explosive eruptions.

Tephra

All solid fragments ejected into the air during a volcanic eruption, ranging in size from fine ash to large blocks and bombs.

Tephra fallout

Volcanic tephra that settles back to the ground from an atmospheric eruption plume.

Ash

Volcanic tephra fragments measuring less than $2\,\text{mm}$ across.

Lapilli

Volcanic tephra fragments ranging between $2\,\text{mm}$ and $64\,\text{mm}$ in diameter.

Blocks

Solid rock fragments larger than $64\,\text{mm}$ that are ejected during an eruption while already solid.

Bombs

Tephra fragments larger than $64\,\text{mm}$ that are molten or partly molten when ejected into the air.

Lahar

A fast-moving volcanic mudflow composed of water, volcanic ash, and debris that behaves like wet concrete.

Pyroclastic flow

A ground-hugging, extremely hot, and fast-moving avalanche of gas, ash, and volcanic rock fragments.

Hot spot

A stationary area where unusually hot mantle material rises to melt overlying rock, creating a chain of volcanoes as a plate moves over it.

Earthquake

Ground shaking caused by the sudden release of stored energy, commonly occurring when rocks slip along a fault.

Elastic rebound theory

The explanation of how stress builds up along a locked fault, deforming rocks until they suddenly slip and rebound toward a less-deformed shape.

Focus (hypocenter)

The specific point inside Earth where an earthquake rupture begins.

Epicenter

The geographic point on Earth's surface located directly above an earthquake's underground focus.

P waves (primary)

The fastest seismic body waves that move with compressional push-pull motion, arrive first, and can travel through solids, liquids, and gases.

S waves (secondary)

Slower seismic body waves with shear side-to-side or up-and-down motion that arrive second and can travel through solids, but not liquids.

Surface waves (L waves)

Seismic waves that propagate along Earth's exterior surface, arrive after body waves, and typically produce the strongest, most damaging shaking.

Seismometer (seismograph)

The instrument used to detect and record seismic ground motion caused by earthquakes.

Seismogram

The visual recording or traced line produced by a seismometer showing ground motion.

Richter scale

A logarithmic magnitude scale based on wave amplitude, where each whole-number increase indicates a $10\times$ increase in wave amplitude and about $31.6$ (rounded to $32$) times the energy.

Mercalli Intensity Scale

An earthquake scale that describes the observed ground shaking and structural damage at a specific location.

Shadow zone

A geographic zone where specific seismic waves are absent because $S$ waves are blocked by the liquid outer core and $P$ waves are refracted.

Seismic tomography

An imaging technique that analyzes seismic-wave velocities to construct three-dimensional internal models of Earth, similar to a CT scan.

Big Bang

The event approximately $13.8\text{ billion years}$ ago that marked the beginning of the universe from an extremely hot, dense initial state that expanded and cooled.

Cosmic Microwave Background (CMB)

Faint remnant thermal radiation from the early universe that was released when space became transparent roughly $380{,}000\text{ years}$ after the Big Bang.

Nebula

A large interstellar cloud of gas and dust where stars can form.

Singularity

A mathematical term used in classical physics to describe an initial Big Bang state of extreme density.

Doppler effect

A change in observed wave frequency due to relative motion between source and observer; light redshifts when moving away and blueshifts when moving closer.

Fusion

The nuclear process of combining lighter atomic nuclei into heavier nuclei, releasing energy that powers stars.

Supernova

A violent stellar explosion that creates and disperses heavy elements into surrounding space.

Dark energy

The unknown physical mechanism or force responsible for the observed accelerating expansion of the universe.

Contour lines

Lines drawn on a map connecting points of equal elevation, where closely spaced lines indicate steep terrain and widely spaced lines indicate gentle slopes.