Earth Science: Tectonics, Weathering, Glaciation, and Geologic Time

Comprehensive practice flashcards reviewing structural geology, fault mechanics, seismology, weathering, soils, glacial morphology, relative and absolute dating, and the geologic time scale based on lecture notes.

How are stress and strain defined and distinguished from each other in geology?

Stress is the force applied per unit area to a rock mass, whereas strain is the resulting change in shape, size, or volume of the rock as a consequence of that stress.

What are the three principal types of differential stress shown in the diagram and their characteristic effects on rock layers?

The three types are: (a) Compression, which pushes rock masses together causing shortening and thickening by folding or faulting; (b) Tension, which pulls rock masses apart causing lengthening and faulting; and (c) Shear stress, which displaces rock masses along closely spaced parallel planes in opposing directions.

How does hydrostatic or confining pressure affect rocks compared to differential stress?

Hydrostatic or confining pressure acts approximately equally in all directions, generally reducing the total volume of a rock without necessarily altering its shape.

What are the characteristics and geological results of elastic, brittle, and ductile deformation?

Elastic deformation is reversible (the rock returns toward its original shape once stress is removed); brittle deformation involves fracturing and breaking, producing joints, fractures, and faults; ductile deformation is permanent change in shape without macroscopic fracture, resulting in folds and ductile shear zones.

What environmental conditions favor brittle versus ductile deformation in rocks?

Brittle deformation is favored by lower temperatures, lower confining pressures, and rapid strain rates. Ductile deformation is favored by higher temperatures, higher confining pressures, and slower strain rates.

Which type of geological fold is depicted in this diagram, where rock layers arch upward and beds dip away from the core?

An anticline, an arch-like fold in which (in a normal, non-overturned sequence) the oldest strata are located at the core or center of the fold.

Which geological fold structure is depicted here, where rock layers form a trough and beds dip toward the core?

A syncline, a trough-like downfold in which (in a normal, non-overturned sequence) the youngest strata are located at the center or core of the fold.

How are domes, basins, and monoclines described structurally?

A dome is an upwarped circular structure where strata dip outward from the center; a basin is a downwarped circular structure where strata dip inward toward the center; and a monocline is a step-like bend or fold in otherwise horizontal sedimentary layers.

In the context of inclined faults, what distinguishes the hanging wall from the footwall?

The hanging wall is the rock block that rests directly above the inclined fault plane, whereas the footwall is the rock block situated below the inclined fault plane.

In the provided normal fault diagram, how do the hanging wall and footwall move relative to each other, and what tectonic stress causes this?

The hanging wall moves downward relative to the footwall under extensional (tensional) stress, which lengthens the crust.

What defines a reverse fault and a thrust fault?

A reverse fault forms under compressional stress, causing the hanging wall to move upward relative to the footwall; a thrust fault is a reverse fault that dips at a low angle.

What are the five consecutive steps described by the elastic rebound model for earthquake generation?

1. Tectonic forces gradually deform rocks. 2. Stress accumulates while friction prevents fault movement. 3. Stress eventually overcomes the resistance to slip. 4. The fault ruptures, releasing stored elastic seismic energy. 5. Seismic waves propagate outward from the source.

In the provided earthquake diagram, what do the terms 'focus' (hypocenter) and 'epicenter' represent?

The focus (hypocenter) is the exact location within Earth's crust where rupture initiates, while the epicenter is the geographic point on Earth's surface directly vertically above the focus.

How do P waves and S waves differ in terms of particle motion, relative velocity, and ability to travel through liquids?

P waves (primary waves) are compressional waves that alternate compression and expansion in the direction of propagation, travel the fastest, and pass through solids, liquids, and gases. S waves (secondary waves) are shear waves with transverse motion perpendicular to propagation, travel slower than P waves, and cannot travel through liquids.

Why was the absence of transmitted S waves through Earth's outer core a crucial geological discovery?

Because S waves cannot propagate through fluids (liquids), the global S-wave shadow zone provided direct seismic evidence confirming that Earth's outer core is in a liquid state.

How do Love waves differ from Rayleigh waves in surface ground motion?

Love waves produce horizontal, side-to-side surface shear motion perpendicular to wave travel, whereas Rayleigh waves produce elliptical, rolling surface motion that includes both vertical and horizontal components.

What is the difference between earthquake magnitude and earthquake intensity?

Magnitude (such as the Moment Magnitude scale, $M_w$) measures the physical size and energy released by an earthquake at its source using seismic instruments; Intensity (measured by the Modified Mercalli Intensity scale, using Roman numerals I to XII) evaluates the observed damage and degree of shaking at a specific geographical location.

By what factor do wave amplitude and released seismic energy increase for each whole-number increase in earthquake magnitude?

Each whole magnitude unit represents approximately a $10\times$ increase in measured wave amplitude and approximately a $32\times$ increase in released seismic energy.

What are the focal depth categories for earthquakes, and what are Wadati-Benioff zones?

Focal depths are shallow ($0\text{ to }70\text{ km}$), intermediate ($70\text{ to }300\text{ km}$), and deep ($300\text{ to }700\text{ km}$). Wadati-Benioff zones are dipping planar zones of seismicity where deep earthquakes trace the descent of subducting lithospheric slabs into the mantle.

What is the fundamental distinction between weathering and erosion?

Weathering is the in situ physical disintegration or chemical alteration of rocks at or near Earth's surface, whereas erosion is the dynamic removal and downslope transport of weathered materials by agents such as water, wind, glacial ice, or gravity.

What mechanical weathering process is illustrated in the diagram, in which water repeatedly freezes, expands, and dislodges rock fragments?

Frost wedging (freeze-thaw weathering), where liquid water enters existing cracks, expands upon freezing, exerts pressure against the rock walls, and progressively widens fractures until rock fragments fall away.

What physical weathering process produces the sheet-like fracture slabs parallel to the rock surface visible on this granitic dome?

Exfoliation (sheeting), caused by unloading and confining pressure release as overlying rock layers are removed by erosion, allowing the rock mass to expand outward and fracture in curved sheets.

What physical weathering process is shown in this image where tree roots grow into fractures and split the rock?

Root wedging, a biological-mechanical weathering process where the growth and radial expansion of plant roots inside pre-existing joints exerts mechanical pressure that forces the rock apart.

How does mechanical weathering enhance the rate of chemical weathering?

Mechanical weathering physically breaks rock masses into smaller fragments, substantially increasing the total surface area exposed to reactive fluids and the atmosphere.

What are the key chemical weathering reactions: dissolution, hydrolysis, oxidation, carbonation, and hydration?

Dissolution: minerals dissolve into solution (e.g., halite); Hydrolysis: water reacts with silicate minerals (e.g., feldspar altering to clay); Oxidation: electron loss involving oxygen to form oxides (e.g., iron-bearing minerals forming iron oxides); Carbonation: carbonic acid reacts with minerals (e.g., limestone dissolution); Hydration: water is directly incorporated into the crystal structure of minerals.

What is the chemical reaction showing the hydrolysis of potassium feldspar into kaolinite clay?

$2\text{KAlSi}_3\text{O}_8 + 2\text{H}^+ + 9\text{H}_2\text{O} \rightarrow \text{Al}_2\text{Si}_2\text{O}_5(\text{OH})_4 + 4\text{H}_4\text{SiO}_4 + 2\text{K}^+$, demonstrating that chemical weathering alters mineral chemistry to produce entirely new secondary minerals.

How does mineral stability at Earth's surface relate to Bowen's reaction series?

Susceptibility to chemical weathering generally follows the reverse of Bowen's reaction series: minerals that crystallize at the highest temperatures and pressures (such as olivine and Ca-rich plagioclase) are least stable and weather most rapidly, whereas low-temperature minerals (like quartz) are highly resistant.

What five major factors govern soil formation according to the acronym CLORPT?

CL — Climate, O — Organisms, R — Relief (topography), P — Parent material, and T — Time.

According to this soil profile diagram, what are the letters assigned to the soil horizons from top to bottom?

O (Organic layer / humus), A (Topsoil with mixed minerals and humus), E (Eluviation layer of leached minerals and organic matter), B (Subsoil zone of accumulation), C (Parent rock / partly weathered rock), and R (Bedrock / unweathered parent rock).

How do eluviation and illuviation differ within a soil profile?

Eluviation is the washing out and leaching of fine clay, iron, or aluminum from upper horizons (such as the E horizon) by percolating water; illuviation is the subsequent deposition and accumulation of these leached materials in lower horizons (such as the B horizon).

What dominant weathering processes and typical soil materials characterize warm humid tropical climates versus arid climates?

Warm, humid tropical climates experience intense chemical weathering and leaching that produce kaolinite, iron- and aluminum-rich residual soils, and laterites. Arid climates experience limited leaching and dominant physical weathering, leading to the accumulation of soluble salts, caliche, and gypsum.

What is the difference between residual soil and transported soil parent material, and what are alluvium and colluvium?

Residual soil forms in place from the underlying bedrock. Transported soil develops on materials moved from elsewhere: alluvium is sediment transported and deposited by flowing water, while colluvium is mass-wasted sediment moved downslope primarily by gravity.

What primary sources of energy drive the global hydrologic cycle?

Solar energy (which drives evaporation and atmospheric air circulation) and gravity (which drives precipitation, runoff, stream flow, and groundwater percolation).

What type of river channel pattern is shown in this aerial photograph, characterized by multiple interconnected channels divided by sediment bars?

A braided river, which develops in settings with high sediment load, variable discharge, and readily erodible banks.

What conditions are required for a river delta to form?

A delta forms where a sediment-laden river enters a standing body of water (such as an ocean or lake), provided the rate of sediment deposition exceeds the rate of sediment removal by waves, currents, and tides.

What are the two major mechanisms by which glacial ice flows downhill?

Internal plastic deformation (internal shear and recrystallization of ice crystals within the glacier) and basal sliding (the entire glacier sliding over bedrock facilitated by liquid meltwater at the base).

How are the accumulation zone, ablation zone, and equilibrium line of a glacier defined?

The accumulation zone is the upper area where annual snowfall exceeds melting; the ablation zone is the lower area where mass loss (melting, sublimation, calving) exceeds snowfall; and the equilibrium line (snowline) is the boundary where annual accumulation equals ablation.

What distinctive glacial landform features are illustrated in this schematic of a glaciated valley?

A glaciated U-valley (U-shaped valley) featuring steep, nearly straight bedrock walls, a broad flat valley floor (often occupied by a river), hanging valleys perched high above the main valley floor, and remnant glacial features.

Identify the sharp, steep-sided alpine landforms produced by glacial erosion shown in this diagram.

Cirques (steep-walled amphitheater basins at valley heads), arêtes (serrated, knife-edge rock ridges between adjacent valleys), cols (low saddles or passes along arêtes), and horns (steep, pyramid-shaped mountain peaks carved by three or more converging cirques).

What is the key sedimentological distinction between glacial till and glacial outwash?

Till is unsorted, unstratified sediment deposited directly by melting glacial ice, whereas outwash is stratified, sorted sand and gravel deposited by glaciofluvial meltwater streams.

What are drumlins, eskers, and kettle lakes in glacial depositional environments?

A drumlin is an asymmetrical, streamlined hill of glacial drift shaped beneath moving ice; an esker is a long, sinuous ridge of stratified sand and gravel deposited by subglacial meltwater streams; and a kettle lake is a water-filled depression formed when a stagnant, buried block of ice melts within glacial drift.

How do glacial expansion and retreat cause eustatic sea-level changes?

During glacial maxima, large volumes of water evaporate from the oceans and become trapped as ice sheets on land, substantially lowering global mean sea level; during interglacials, ice melt returns water to the ocean basins, raising global sea level.

What is the age of Earth, and what are the four formal eons of the geologic time scale?

Earth formed approximately $4.54\text{ Ga}$ ($4.567\text{ Ga}$ begin of Hadean). The four eons are the Hadean ($4.567\text{--}4.031\text{ Ga}$), Archean ($4.031\text{--}2.5\text{ Ga}$), Proterozoic ($2.5\text{ Ga--}538.8\text{ Ma}$), and Phanerozoic ($538.8\text{ Ma to present}$).

What percentage of Earth's total geological history is represented by the Precambrian?

Nearly $88\%$ of Earth's history, spanning the Hadean, Archean, and Proterozoic eons prior to the beginning of the Cambrian period.

What are the three eras that comprise the Phanerozoic Eon, along with their numerical age boundaries?

The Paleozoic Era ($538.8\text{--}251.9\text{ Ma}$), the Mesozoic Era ($251.9\text{--}66.0\text{ Ma}$), and the Cenozoic Era ($66.0\text{ Ma to present}$).

Which fundamental geological principle is depicted here, stating that in an undeformed sequence, the oldest layers are at the bottom and youngest at the top?

The Principle (or Law) of Superposition.

Which geological principle is illustrated by layers being deposited flat before undergoing tilting?

The Law of Original Horizontality, which states that layers of sedimentary rock are originally deposited in approximately flat, horizontal beds under the influence of gravity.

Which stratigraphic principle explains why sedimentary rock layers on either side of an erosional canyon can be correlated as formerly continuous strata?

The Principle of Lateral Continuity, which establishes that sedimentary layers originally spread out laterally in all directions until they pinch out, thin, or reach the margin of their depositional basin.

According to the principle demonstrated in this block diagram, what is the age relationship between intrusive dikes or faults and the sedimentary rock layers they cut across?

According to the Principle of Cross-Cutting Relationships, an igneous intrusion (e.g., Dike A, Dike B) or fault (e.g., Fault A, Fault B) must be younger than the rock units or geological structures that it cuts across.

What does the Principle of Inclusion state regarding the relative age of the rock clasts versus the host rock containing them?

The Principle of Inclusion states that clasts or fragments of older rock contained within another rock are older than the host rock that encloses them, because the source rock had to exist before the fragments could be weathered, eroded, and incorporated.

In the context of the depicted magmatic intrusion, what are xenoliths and the 'baked' zone?

Xenoliths are pieces of pre-existing older country rock torn free and incorporated into invading magma without completely melting; the baked zone is the zone of country rock along the contact that was thermally metamorphosed by the heat of the intrusion.

What type of unconformity is illustrated here, where parallel sedimentary strata are separated by an erosional or nondepositional surface?

A disconformity, where the sedimentary beds above and below the erosional boundary remain parallel to one another.

Which type of unconformity is depicted, characterized by younger horizontal sedimentary layers overlying tilted, eroded sedimentary rocks?

An angular unconformity, representing a gap in the rock record produced by folding or tilting of older strata, uplift, erosion, and subsequent renewed deposition of flat-lying sediments.

In the diagram, surface 'A' separates older igneous/metamorphic rocks from younger overlying sedimentary rocks. What type of unconformity is this?

A nonconformity, which occurs where sedimentary strata are deposited directly on an eroded surface of crystalline igneous or metamorphic basement rocks.

What principle allows rock strata across separated canyon walls to be chronologically correlated using specific fossil groups?

The Principle of Faunal Succession, which recognizes that fossilized species succeed one another in a definite, recognizable chronological order through geologic time.

What characteristics make an organism an effective index fossil?

An ideal index fossil belonged to an organism that was geographically widespread, abundant, easily identifiable, and existed for a relatively short span of geologic time.

What are the parent isotopes, daughter isotopes, and half-lives of the Carbon-14 and Potassium-40 radiometric dating systems?

Carbon-14 decays to Nitrogen-14 ($\text{C-14} \rightarrow \text{N-14}$) with a half-life of $5\text{,}730\text{ years}$; Potassium-40 decays to Argon-40 ($\text{K-40} \rightarrow \text{Ar-40}$) with a half-life of $1.25\text{ billion years}$.

What are the half-lives of the Uranium-238, Uranium-235, Rubidium-87, and Samarium-147 isotopic systems?

Uranium-238 to Lead-206 ($\text{U-238} \rightarrow \text{Pb-206}$): $4.47\text{ billion years}$; Uranium-235 to Lead-207 ($\text{U-235} \rightarrow \text{Pb-207}$): $704\text{ million years}$; Rubidium-87 to Strontium-87 ($\text{Rb-87} \rightarrow \text{Sr-87}$): $48.8\text{ billion years}$; and Samarium-147 to Neodymium-143 ($\text{Sm-147} \rightarrow \text{Nd-143}$): $106\text{ billion years}$.

Why is Carbon-14 dating unsuitable for determining the age of Earth or dating non-avian dinosaur fossils?

Because Carbon-14 has a short half-life ($5\text{,}730\text{ years}$), almost all detectable parent $\text{C-14}$ decays away within approximately $50\text{,}000\text{ years}$. Since dinosaur fossils are tens of millions of years old and Earth is billions of years old, no measurable $\text{C-14}$ remains.

How do geologists determine the depositional age of sedimentary rocks using detrital zircons and volcanic ash beds?

Because detrital grains are older than the sedimentary rock containing them, the youngest detrital zircon date provides a maximum depositional age. Numerical ages of interbedded or cross-cutting volcanic ash beds are then used to bracket the precise depositional age.

What early evidence indicates the presence of liquid water on Earth by approximately 4.4 Ga?

Isotopic geochemical signatures preserved within ancient detrital zircon crystals indicate that liquid water and surface weathering likely existed on Earth by about $4.4\text{ Ga}$.

What are stromatolites and when does widely accepted evidence of microbial life first appear in the rock record?

Stromatolites are layered sedimentary structures formed by the trapping, binding, and mineral precipitation activities of microbial mats. The earliest widely accepted evidence for microbial life appears in Archean rocks approximately $3.5\text{ Ga}$.

What was the Great Oxidation Event, and when did it occur?

Occurring between approximately $2.4\text{ and }2.1\text{ Ga}$, the Great Oxidation Event was a major rise in atmospheric oxygen generated by photosynthetic cyanobacteria, which fundamentally transformed atmospheric chemistry, surface environments, and Earth's mineral diversity.

When did the Cambrian Period begin, and what biological development characterizes this boundary?

The Cambrian Period began at approximately $539\text{ Ma}$ (or $538.8\text{ Ma}$), marked by the Cambrian Explosion, an extraordinary evolutionary diversification of animal phyla and the widespread appearance of mineralized hard skeletons in the fossil record.

What are the approximate dates and identities of the 'Big Five' Phanerozoic mass extinction events?

1. End-Ordovician ($444\text{ Ma}$); 2. Late Devonian ($\approx 372\text{--}359\text{ Ma}$); 3. End-Permian ($251.9\text{ Ma}$, the largest mass extinction in Earth history); 4. End-Triassic ($\approx 201\text{ Ma}$); and 5. End-Cretaceous ($66\text{ Ma}$, famously linked to the Chicxulub asteroid impact).