Earth's External Processes

• Earth's external processes include weathering, mass wasting, and erosion, which shape the Earth's surface.

Weathering

• Weathering involves chemical and physical processes that disintegrate rocks on Earth's surface.

Mass Wasting

• Mass wasting is the movement of rock, soil, and regolith downhill due to gravity.

Erosion

• Erosion is where mobile agents remove broken-down materials.
• Mobile agents include water, wind, ice, and gravity.

Types of Mechanical Weathering

• Frost wedging: water freezes and expands in cracks.
• Salt crystal growth: salt crystals grow and exert pressure.
• Sheeting/unloading: reduces pressure, causing expansion and fracturing.
• Biological activity: plants and animals break down rocks.

Types of Chemical Weathering

• Dissolution: minerals dissolve in water.
• Oxidation: minerals react with oxygen.
• Hydrolysis: minerals react with water, changing its chemical structure.

Controls of Soil Formation

• Parent material: the original rock that breaks down to form soil.
• Time: how long the soil has been developing.
• Climate: temperature and precipitation patterns.
• Plants and animals: organic matter and biological activity.
• Topography: the shape and slope of the land.

Soil Profile

• O horizon: organic matter.
• A horizon: topsoil, rich in organic matter.
• E horizon: zone of leaching (eluviation), where minerals are dissolved and carried away.
• B horizon: subsoil, accumulation of leached minerals.
• C horizon: partially altered parent material.
• True soil consists of O, A, E, and B horizons.

Types of Sedimentary Rocks

• Detrital sedimentary rocks: formed from fragments of other rocks.
• Chemical sedimentary rocks: minerals precipitate out of solution.

Detrital Sedimentary Rocks

• Composed of physical fragments such as sand, silt, clay, or gravel.
• Examples include shale, sandstone, conglomerate, and breccia.

Chemical Sedimentary Rocks

• Formed when minerals precipitate from a solution, often water.

• Examples include limestone, chert, and rock salt.

• Shale is the most common sedimentary rock.

• Limestone is the most common chemical sedimentary rock.

• Travertine is the most common inorganic limestone.

Diagenesis

• Encompasses the chemical, physical, and biological changes that occur after sediment deposition and burial.

Lithification

• Lithification transforms loose sediments into solid rock.
• Compaction occurs as sediments are pressed together under their own weight.
• Cementation is the process of minerals crystallizing among sediment grains.

Agents of Metamorphism

• Heat
• Confining pressure
• Differential stress
• Chemically active fluids
• Heat is the most important agent.

Metamorphic Textures

• Foliated: minerals are aligned in a parallel manner.
• Non-foliated: minerals are not aligned.

Foliated Metamorphic Textures

• Rock or slaty cleavage: rocks split into thin sheets.
• Schistosity: platy minerals are visible and aligned.
• Gneissic: minerals are segregated into bands.

Non-Foliated Metamorphic Textures

• Porphyroblastic: large crystals in a fine-grained matrix.
• Marble.
• Quartzite.

Common Foliated Metamorphic Rocks

• Shale transforms into slate.
• Slate becomes phyllite.
• Phyllite becomes schist.
• Schist becomes gneiss.

Common Non-Foliated Rocks

• Marble forms from limestone.
• Quartzite forms from sandstone.
• Hornfels forms from shale.