Earth Science: Weathering, Erosion, and Water Distribution

Endogenic processes

Internal geological forces within Earth that shape its structure through plate boundaries, volcanism, and more.

Exogenic processes

External forces at Earth's surface that wear down rocks and reshape landscapes.

Weathering

The physical breakdown (disintegration) and chemical alteration (decomposition) of rocks at or near Earth's surface.

Erosion

The removal of weathered rocks and minerals by moving water, wind, glaciers, and gravity.

Mass wasting

Movement of earth materials (soil, rocks, etc.) downslope primarily under the influence of gravity.

Angle of repose

Maximum slope or steepness at which loose material remains stable without sliding.

Suspension

Particles carried in water.

Solution

Dissolved minerals.

Traction

Rolling along the riverbed.

Saltation

Bouncing of particles.

Chemical Weathering

Decomposition of rocks through chemical reactions.

Physical/Mechanical weathering

Breaks rocks into pieces without changing chemical composition.

Frost wedging

Rainwater enters cracks, freezes, expands, and causes cracks to widen.

Dissolution

Slightly acidic rainwater dissolves minerals, such as in limestone dissolution.

Abrasion

Particles like sand strike rock surfaces, wearing them down.

Temperature

Cause rocks to expand and contract, leading to cracking and breaking.

Biological Activities

Plants, animals, and microorganisms contribute to weathering.

Root wedging

Plant roots grow into cracks and break rocks.

Mining

Deep rocks exposed; machinery causes physical disturbance.

Deforestation

Removes protection from water/wind and increases exposure to erosion.

Salt Crystal Growth

Salty water in cracks evaporates, crystals grow, and put pressure on rock.

Exfoliation

Large rock masses exposed to lower pressure expand and crack into thin layers.

Oxidation

Oxygen reacts with minerals, forming oxides like rust on iron-rich rocks.

Hydrolysis

Water reacts with minerals, forming new minerals and breaking down rock.

Biological Weathering

Caused by living organisms, can be physical (root wedging) or chemical (acids from decaying matter).

Acidic Rain

Dissolves minerals, roughening surface (solution/dissolution).

Relative Dating

Sequencing rock layers (which formed first).

Absolute Dating

Determining actual age of rocks/fossils using radiometric methods.

Faunal Succession

Fossils succeed one another in a predictable order → useful for relative dating.

Geologic Time Scale (GTS)

Timeline of major Earth events from formation (~4.6 billion years ago) to present.

Water cycle

Movement of water between oceans, land, and atmosphere through evaporation, condensation, precipitation, and runoff.

Brackish water

Mix of salt and freshwater; found in estuaries, deltas, mangroves, coastal wetlands.

Paradox of plenty

Earth looks water-rich, but usable freshwater is scarce.

Polarity

Oxygen slightly negative, hydrogen slightly positive → allows hydrogen bonding.

Cohesion

Water sticks to itself → droplets.

Adhesion

Water sticks to surfaces.

High specific heat

Resists temperature changes.

Universal solvent

Dissolves many substances.

Capillary action

Movement through narrow spaces without gravity; essential for water transport in plants.

Evaporative cooling

Heat loss through evaporation → regulates temperature in organisms.