Geology Exam 1

What markers of human civilization can geologists use as evidence?

Plastics, chemical layers, banded iron formations, and stromatolites

What are stromatolites?

Layered structures formed by mats of algae (cyanobacteria) trapping and binding sediments. They are some of the earliest evidence of life on Earth.

How old is Earth, and when did primitive life appear?

Earth is about 4.6 billion years old; primitive anaerobic prokaryotes appeared by 3.8 billion years ago.

What are the three main rock types and how do they form?

• Igneous – Form from cooling magma/lava.

• Sedimentary – Form from erosion, deposition, and cementation of particles.

• Metamorphic – Form when preexisting rocks are changed by heat and pressure without melting.

Mnemonic for rock layers

Mnemonic: “I See Mountains”

• I = Igneous (fire-born)

• S = Sedimentary (stacked layers)

• M = Metamorphic (morphed by heat/pressure)

Define metamorphism

The process by which preexisting rocks are altered by heat, pressure, or chemically active fluids, without complete melting

Define subduction

A geologic process where one tectonic plate is forced beneath another into the mantle, recycling crustal material and driving volcanism and earthquakes

What evidence supports the Big Bang theory?

The redshift of galaxies (Doppler Effect), cosmic microwave background radiation, and computer models

What is the Doppler Effect and why is it important in geology/astronomy?

The change in wavelength of waves (sound or light) caused by the motion of the source relative to the observer. For light, objects moving away stretch to longer wavelengths (redshift). This shows that the universe is expanding, supporting the Big Bang theory.

How old is the universe estimated to be?

About 13.7 billion years

What are chondrite meteorites and why are they important?

Stony meteorites that contain small, round mineral grains called chondrules. They are chemically similar to the material that formed the solar system, making them valuable for dating the age of the Earth and Sun.

What defines a mineral?

A naturally occurring, inorganic solid with a definite chemical composition and crystal structure.

What are silicates and why are they important?

Minerals that contain silicon and oxygen, the two most abundant elements in Earth’s crust. They are the most common mineral group and include quartz and feldspar, which form the building blocks of most rocks.

What does the principle of superposition state?

Older layers are deposited first, younger layers are on top

What is the principle of cross-cutting relationships?

Any feature cutting across a rock layer is younger than the rock it cuts.

What are index fossils, and why are they useful?

Fossils of species that were widespread but only existed for a relatively short period. They help date rock layers and correlate strata across different regions.

What is porosity vs. permeability?

• Porosity: % of void space in a rock

• Permeability: How easily fluids move through it

What are the three main types of stress in rocks?

Tensional (pulling apart), compressional (squeezing), and shear (sliding past)

How does Montgomery connect stress and strain to hazards?

Stress and strain explain how rocks deform and break, which helps us understand earthquakes, landslides, and other natural hazards.

What is the biggest global environmental challenge?

Exponential human population growth (affects sustainability, economy, and Earth’s carrying capacity).

What are Earth’s four main systems?

HABG: Hydrosphere, Atmosphere, Biosphere, Geosphere.

What is uniformitarianism?

The principle that geologic processes operating today have also operated in the past (“the present is the key to the past”).

When did oxygenation of the atmosphere occur, and why is it important?

2.3 billion years ago; it allowed eukaryotes and multicellular life to evolve.

When did “hard parts” (like shells and bones) appear?

About 0.5 billion years ago.

How are the rock cycle and plate tectonic cycle connected?

Plate tectonics drive volcanism (igneous), metamorphism, uplift/weathering (sediments), and subduction, fueling the rock cycle.

Who proposed convection cells drive plate motion?

Harry Hess.

What is convection?

Heat causes material to become less dense and rise, cool, become denser, and sink — creating a cycle that moves Earth’s plates.

Why is plate tectonics called the “grand unifying theory”?

Because it explains volcanism, earthquakes, mountain building, and the rock cycle.

What is the sulfur cycle?

Movement of sulfur through atmosphere, hydrosphere, biosphere, and geosphere, controlled by biological and geological processes.

How do cycles work in geology?

Elements aren’t lost or destroyed; they move through natural reservoirs (rocks, oceans, atmosphere) by various fluxes.

How to remember the sulfur cycle steps?

“VANS” → Volcanic release → Atmospheric transport → Nutrient uptake → Sediment burial.

Dating Principles

“Some Old Laws Count” → Superposition, Original Horizontality, Lateral Continuity, Cross-cutting.

What is the Doppler Effect in light and sound?

A shift in wave frequency due to relative motion.

• For sound: an ambulance siren sounds higher when approaching, lower when moving away.
  
  

For light: galaxies moving away show redshift, proving cosmic expansion.

 What is the solar system mostly made of?

Hydrogen and helium, with small amounts of lithium, beryllium, boron, and higher levels of iron.

What explains the odd-even differences in element abundance?

Elements with even atomic numbers are more common because they are more stable during nuclear fusion in stars.

What happens in stars like our Sun after hydrogen is used up?

Helium burning begins, creating carbon “ash.” The star expands into a red giant, eventually shedding material.

What happens in stars more massive than the Sun?

They burn hydrogen quickly, fuse heavier elements up to iron, and develop an “onion-like layered structure.”

How are elements heavier than iron formed?

By novae and supernovae explosions (nucleosynthesis beyond iron).

What is the implication of nucleosynthesis?

Our Sun is at least a second-generation star, formed from supernova debris mixed with primordial hydrogen and helium.

What is the Solar Nebular Theory?

Planets formed from a rotating disk of gas and dust around the young Sun (~4.6 billion years ago).

Evidence:

1. Planetary orbits are in a flat disk.
   
   

2. Rocky planets are near the Sun; gas giants farther away.
   
   

3. Planets orbit in the same direction.
   
   

Mnemonic:“OCP” → Orbits, Composition, Plane.

What caused Earth’s seasons?

A giant impact that formed the Moon also tilted Earth’s axis.

What are chondrite meteorites?

Primitive stony meteorites with silicate minerals that preserve early solar system material.

What are the main meteorite types?

• Stony – silicate minerals
  
  

• Iron – metallic iron
  
  

Stony-Iron – a mix of both

 How old are meteorites, Moon rocks, and Earth rocks?

Meteorites: ~4.56 Ga, Moon rocks: ~4.5 Ga, oldest Earth rocks: ~4.37 Ga.

What is Earth’s differentiation?

Separation of materials by density: heavy metals sank to the core, lighter silicates formed crust

How did the Moon form?

From debris after a Mars-sized impact with early Earth; this also tilted Earth’s axis.

What did early Earth look like?

Hot with rapid mantle heat flow, small tectonic plates, and proto-continents forming.

What are the 5 defining characteristics of a mineral?

Naturally occurring, inorganic, solid, definite chemical composition, crystalline structure.
Mnemonic: NISDC → “Nice Ice Solid, Defined Crystals”

What are the main physical properties used to identify minerals?

Color, hardness, density, cleavage, streak.
Mnemonic: CHaD CaS (Color, Hardness, Density, Cleavage, Streak).

What are ferromagnesian silicates?

Silicates containing iron/magnesium, dark-colored, weather easily (e.g., olivine).

 Name the 6 groups of non-silicate minerals with examples.

• Oxides → Hematite (Fe₂O₃)

• Carbonates → Calcite (CaCO₃)

• Sulfates → Gypsum (CaSO₄)

• Sulfides → Pyrite (FeS₂)

• Halides → Halite (NaCl)

Native elements → Gold (Au)
Mnemonic:OCCSSH → “Only Cool Scientists Study Hard Native-elements.

How do igneous rocks form?

From cooling and solidification of magma/lava.

What’s the difference between intrusive and extrusive igneous rocks?

Intrusive = cool slowly underground → large crystals.
Extrusive = cool quickly at surface → small crystals or glassy.
Mnemonic: ICE → Intrusive = Crystals Enlarged.

Diagram (Plutonic vs Volcanic): Shows magma cooling underground → big crystals; lava cooling at surface → fine or glassy texture.

What are sediments and how are they deposited?

Loose material deposited by water, air, ice, or gravity.

What are the 3 types of sedimentary rocks?

 Clastic (mechanical weathering), chemical (precipitation), biogenic (biological shells).
Mnemonic: CCB → “Clastic, Chemical, Biogenic”.

Why are sedimentary rocks important?

Cover 75% of land, preserve Earth’s history (fossils, past environments).

Diagram (Sediment Types): Side-by-side images of sand grains (clastic), fossil shells (biogenic), and halite crystals (chemical)

How do metamorphic rocks form?

From preexisting rocks under heat and pressure without melting.

What is foliation?

Banding/planes of minerals due to pressure (e.g., schist, gneiss).

Examples of metamorphic rocks

Shale → Schist, Granite → Gneiss

Diagram (Metamorphism): Shows arrows for heat/pressure turning sedimentary or igneous rocks into layered, banded metamorphic rocks.

What is the rock cycle?

The process of rocks changing between igneous, sedimentary, and metamorphic through melting, cooling, weathering, and pressure.

Step-by-step mnemonic:

1. Iggy (Igneous)

2. Said (Sedimentary)

3. Metamorphosis (Metamorphic)

4. Rules! (Cycle continues via melting & cooling)

So: “Iggy Said Metamorphosis Rules.”

What is porosity?

The % of void space in a rock.

What is permeability?

The ability of fluids to move through rock.

Which rock type usually has the highest porosity & permeability?

Sedimentary (especially sandstone).

What are the 3 main types of stress?

Compressive (squeezing), Tensile (pulling apart), Shear (sliding)

What are the 3 types of deformation (strain)?

Elastic (temporary), Plastic/Ductile (permanent bend), Brittle/Rupture (break).

What affects porosity & permeability?

• More cementation → lower P/P

• Larger, uniform grains → higher P/P

• More fractures → higher permeability

Diagram: Sandstone with big pores (high porosity), shale with tiny pores (low porosity).

What is stratigraphy?

The study of rock layers and their relationships in time and space.

 Principle of Superposition?

Oldest layers on bottom, youngest on top.

Principle of Original Horizontality?

 Sedimentary layers are originally deposited flat; tilting/folding occurs later.

Principle of Lateral Continuity?

Layers extend laterally until cut off by erosion/faulting.

Principle of Cross-Cutting Relationships?

A rock/fault cutting another layer is younger than the layer it cuts.

Diagram: Shows stacked rock layers (superposition), tilted layers (horizontality), continuous beds across valleys (lateral continuity), and an igneous dike cutting across layers (cross-cutting).

What is biostratigraphy?

Using fossils to correlate rock layers and determine relative ages.

What makes a good index fossil?

Widespread, abundant, short geologic range, easily identifiable.

Diagram: Example of a Devonian fossil (Mucrospirifer mucronatus) used to identify that time period.

What is paleomagnetism?

The study of magnetic minerals in rocks that align with Earth’s magnetic north as they form.

How is paleomagnetism used for dating?

By matching the magnetic patterns in rocks to the worldwide polarity record.

When was the last magnetic reversal?

About 780,000 years ago.

What is tephrochronology?

Dating volcanic eruptions using tephra (lava, ash, pumice, volcanic glass).

Tephra = Time from Eruption’s Fingerprint

Why is volcanic glass useful for dating?

Each eruption has a unique chemical fingerprint, which can be matched to identify when/where it occurred.

What is absolute dating?

A method to estimate a specific chronological age in years (with a margin of error).

Why is absolute dating often preferred?

Because it gives exact ages if the right material is available.

What isotopes of carbon exist?

C-12, C-13 (stable), C-14 (unstable).

What is the half-life of carbon-14?

5,730 years.

What is the useful dating range for radiocarbon?

Between 50 years and 50,000 years old.

What material is potassium-argon dating used on?

Volcanic minerals.

What is its dating range?

From 100,000 years up to the age of Earth (~4.6 billion years).

What is the half-life of Uranium-Thorium?

About 245,000 years.

How is disequilibrium dating done?

By measuring how much balance has been restored between parent ^234U and daughter ^230Th, compared with ^238U.

Why are magadi cherts useful?

They contain a lot of uranium but little initial thorium, which makes age calculation easier.

What do trapped electron dating methods measure? What is one example of this method?

Radiation exposure (from sunlight, heat, etc.) trapped in objects.

OSL (Optically Stimulated Luminescence).

Diagram descriptions (5)

• Paleomagnetism diagram (not shown but implied): Would show stripes of normal and reversed polarity in rocks, like barcodes, matched to Earth’s reversal history.

• Tephra diagram: Likely shows volcanic ash layers with chemical “fingerprints.”

• Carbon dating diagram: Usually shows exponential decay curve of C-14 vs. time.

• Potassium-Argon/Uranium diagrams: Typically show decay chains (parent isotope → daughter isotope).

• Trapped electron diagram: Often shows light signal being released when sample is stimulated.