Earth Science: Metamorphism, Plate Tectonics, and Geologic Dating

Agents of metamorphism

Factors that cause changes in the mineralogy, texture, and chemical composition of rocks, including temperature, pressure, and chemically active fluids.

Geothermal gradient

The rate at which temperature increases with depth in the Earth's crust, typically measured in degrees Celsius per kilometer.

Metamorphic Grade

A classification of metamorphic rocks based on the intensity of metamorphism, which affects the mineral composition and texture.

Protolith

The original, unmetamorphosed rock from which a metamorphic rock forms.

Changes during metamorphism

Alterations in mineral composition, texture, and structure of rocks due to changes in temperature, pressure, and chemical environment.

Metamorphic textures (e.g., foliation)

The physical arrangement of minerals in metamorphic rocks, with foliation referring to the parallel alignment of platy minerals.

Index minerals

Minerals that are stable under specific temperature and pressure conditions, used to determine the metamorphic grade of rocks.

Metamorphic Zones

Regions within the Earth's crust where specific metamorphic conditions prevail, often defined by the presence of certain index minerals.

Contact vs. Regional Metamorphism

Contact metamorphism occurs due to heat from nearby molten rock, while regional metamorphism occurs over large areas under high pressure and temperature.

Alfred Wegener

A German meteorologist and geophysicist known for proposing the theory of continental drift.

Evidence for Continental Drift

Fossil distribution, geological similarities, and the fit of continental margins support the theory that continents were once joined.

Pangea & Gondwana

Pangea is the supercontinent that existed during the late Paleozoic era, while Gondwana was a southern supercontinent that included present-day Africa, South America, and Antarctica.

Strike & Dip

Strike is the direction of the line formed by the intersection of a horizontal plane with an inclined surface, while dip is the angle at which the surface inclines from the horizontal.

Stress vs. Strain

Stress is the force applied to a material, while strain is the deformation that occurs as a result of that stress.

Elastic, Plastic, Ductile, Brittle

Elastic materials return to their original shape after stress, plastic materials deform permanently, ductile materials can be stretched, and brittle materials fracture.

Brittle vs. Ductile

Brittle materials break under stress, while ductile materials can deform without breaking.

Joints vs. Faults

Joints are fractures in rocks without movement, while faults are fractures where movement has occurred.

Dip-Slip vs. Strike-Slip

Dip-slip faults involve vertical movement, while strike-slip faults involve horizontal movement.

Normal, Reverse & Thrust Faults

Normal faults occur when the hanging wall moves down, reverse faults occur when the hanging wall moves up, and thrust faults are a type of reverse fault with a low-angle fault plane.

Transform Faults

Faults where two tectonic plates slide past each other horizontally.

Hanging Wall vs. Footwall

The hanging wall is the block of rock above a fault, while the footwall is the block below.

Motion of walls in each fault

In normal faults, the hanging wall moves down; in reverse faults, it moves up; and in strike-slip faults, the walls move horizontally.

Compression or extension vs. fault type

Compression leads to reverse and thrust faults, while extension leads to normal faults.

Right-lateral vs. Left-lateral

In right-lateral faults, the opposite side moves to the right, while in left-lateral faults, it moves to the left when viewed from one side.

Anticline vs. Syncline

Anticlines are upward-arching folds, while synclines are downward-arching folds in rock layers.

Folds: Axis, Limb, Hinge, Axial Plane

The axis is the line along which a fold is bent, limbs are the sides of the fold, the hinge is the point of maximum curvature, and the axial plane divides the fold symmetrically.

Domes & Basins

Domes are upward bulges of rock layers, while basins are downward depressions.

Position vs. Age of rocks in anticlines & synclines

In anticlines, older rocks are found at the center, while in synclines, younger rocks are at the center.

Mountains

Elevated landforms that rise prominently above their surroundings, often formed by tectonic forces.

Continental Shield

A large area of exposed Precambrian crystalline rocks that form the ancient geological core of continents.

Active vs. Passive Margins

Active margins are tectonically active with earthquakes and volcanoes, while passive margins are stable and have little tectonic activity.

Orogenesis & Orogeny

Orogenesis refers to the process of mountain building, while orogeny is a specific event that contributes to the formation of mountains.

Terrane

A fragment of crustal material that has a distinct geological history, often differing from the surrounding areas.

Weathering vs. Erosion

Weathering is the breakdown of rocks at their location, while erosion is the movement of weathered material from one location to another.

Physical Weathering

The mechanical breakdown of rocks into smaller pieces without changing their chemical composition.

Chemical Weathering

The breakdown of rocks through chemical reactions, altering their mineral composition.

Mechanical Weathering

The process of physically breaking rocks into smaller fragments without changing their chemical structure.

Dissolution

The process by which minerals dissolve in water, often leading to the formation of caves.

Hydrolysis

A chemical weathering process where water reacts with minerals to form new minerals and soluble salts.

Oxidation

A chemical weathering process where minerals react with oxygen, often resulting in rusting of iron-bearing minerals.

Regolith

The layer of loose, unconsolidated material covering solid rock, including soil and broken rock.

Soil

The upper layer of earth in which plants grow, consisting of organic matter, minerals, gases, liquids, and organisms.

Humus

The organic component of soil formed by the decomposition of plant and animal matter.

Soil Formation

The process by which soil develops from weathered rock and organic material over time.

Soil Profile

A vertical section of soil that displays its layers, called horizons, which vary in composition and characteristics.

Turbidity Current

A fast-moving flow of sediment-laden water that occurs underwater, often triggered by disturbances like earthquakes.

Graded Bed

A sedimentary layer that shows a gradual change in grain size from coarse at the bottom to fine at the top.

Deep-Sea Fan

A fan-shaped deposit of sediment that forms on the ocean floor at the base of a continental slope.

Alluvial Fan

A fan-shaped deposit of sediment formed where a river flows from a steep area onto a flatter plain.

Relative vs. Numerical Dating

Relative dating determines the sequence of events, while numerical dating provides an actual age or date for an event.

Geologic principles

Fundamental concepts used to understand geological processes and the history of the Earth, including uniformitarianism and superposition.

Uniformitarianism

The principle that the processes operating in the present are the same as those that operated in the past.

Included Fragments

Pieces of older rock that are found within a younger rock layer, indicating the relative ages of the rocks.

Biotic Succession

The principle that different types of organisms succeed one another in a predictable manner over geological time.

Biostratigraphy

The branch of stratigraphy that uses fossil organisms to date and correlate rock layers.

Index fossils

Fossils of organisms that were widespread but only existed for a short geological time, used to date rock layers.

Stratigraphic range

The time span during which a particular fossil or rock layer is found in the geological record.

Types of Unconformities

Discontinuities in the geological record, including angular unconformities, disconformities, and nonconformities.

Geologic Time Scale (Eon, etc.)

A system of chronological dating that relates geological strata to time, divided into eons, eras, periods, epochs, and ages.

Radioactive Decay

The process by which an unstable atomic nucleus loses energy by emitting radiation, leading to the transformation into a different element.

Parent vs. Daughter

In radioactive decay, the parent is the original unstable isotope, while the daughter is the stable product of the decay.

Radioactive Half-Life

The time required for half of the radioactive atoms in a sample to decay into their daughter isotopes.

Thermohaline circulation

The global circulation of ocean water driven by differences in temperature and salinity, affecting climate and weather patterns.

Upwelling

The process where deep, cold, nutrient-rich water rises to the surface, often supporting high biological productivity.

Downwelling

The process where surface water sinks into the ocean, often occurring in areas where water becomes denser.

Climate change

Long-term alterations in temperature, precipitation, and other atmospheric conditions on Earth.

Greenhouse effect

The warming of the Earth's surface due to the trapping of heat by greenhouse gases in the atmosphere.

Coriolis

The apparent deflection of moving objects (like air and water) due to the rotation of the Earth.

Ekman

A concept in oceanography describing the effect of wind on ocean currents, resulting in a spiral movement of water.

Reservoir

A natural or artificial lake where water is stored, often used for water supply, irrigation, or hydroelectric power.

Flux

The rate of flow of a property (such as energy or mass) through a surface or across a boundary.

Oxygen Isotopes

Variants of oxygen atoms with different numbers of neutrons, used in paleoclimatology to infer past temperatures.

Weather vs. Climate

Weather refers to short-term atmospheric conditions, while climate refers to the long-term average of weather patterns in a region.