ESCI 1001 Lecture Notes
Module 1: Why We Study Earth
What Is Geology?
Geology is "Earth knowledge", the scientific study of our planet. It encompasses:
Earth’s history: Understanding the timeline of events that have shaped the planet.
Earth’s composition: Identifying the elements and compounds that make up the Earth.
Earth’s internal structure: Studying the layers and zones within the Earth, such as the crust, mantle, and core.
Earth’s surface features: Examining landforms and geological formations on the Earth’s surface.
What is Earth Science?
"Earth knowledge,” the scientific study of our planet including:
Earth’s history: Exploring major geological events and changes over millions of years.
Earth’s composition: Analyzing the chemical and mineral makeup of the Earth.
Earth’s internal structure: Investigating the properties and dynamics of the Earth's interior.
Earth’s surface features: Describing and classifying various surface features and their formation processes.
Science for Sustainable Development
Earth is viewed as a “spaceship” with finite resources and a delicate life-support system, emphasizing the need for careful management.
"Sustainable Development": The current generation has a responsibility to maintain a hospitable planet for future generations by using resources wisely and minimizing environmental impact.
Thought Questions:
Earth’s population is expected to increase by over one billion in twenty years (approximately a 12.5% increase), raising questions about resource availability and environmental impact.
Is this sustainable? Evaluate whether current practices can support such growth.
What must humans do to achieve sustainability? Consider changes in consumption, technology, and policy.
The Roles of Earth Scientists
Find and manage NATURAL RESOURCES, including energy sources, minerals, and water, to meet societal needs.
Understand Earth processes well enough to predict NATURAL HAZARDS such as earthquakes, volcanic eruptions, and landslides, to mitigate their impact.
Protect the environment by understanding ENVIRONMENTAL AND GLOBAL CHANGE, including climate change, pollution, and deforestation, to develop strategies for conservation and remediation.
Geologist's Workplace:
Fieldwork: Conducting on-site investigations and collecting data in various geological settings.
Laboratory: Analyzing samples and conducting experiments to understand Earth materials and processes.
Computer: Using software for data analysis, modeling, and simulation of geological phenomena.
Natural Resources (and Reserves)
Discovered resources: Resources that have been identified through exploration and mapping.
Deposits known and recoverable today (reserves): Resources that are economically viable to extract with current technology.
Deposits known but not recoverable today: Resources that are known but cannot be extracted economically or with current technology.
Undiscovered resources: Resources that are hypothesized to exist but have not yet been discovered.
Hypothetical deposits: Potential resources based on geological models and regional surveys.
There is an increasing certainty of existence from undiscovered to discovered resources, as well as varying feasibility of economic recovery based on technology and market conditions.
Types of Resources
Energy (oil, coal, solar), Material (minerals, metals), Water (surface water, groundwater)
What is a renewable resource? A resource that can be replenished naturally over a relatively short period (e.g., solar, wind, water).
What is a nonrenewable resource? A resource that exists in a finite amount and cannot be easily replaced (e.g., oil, coal, minerals).
What is a sustainable resource? A resource that is used in a way that meets the needs of the present without compromising the ability of future generations to meet their own needs.
Energy Resources
Global primary energy consumption by source, showing the distribution of energy types used worldwide.
Primary energy is based on the substitution method and measured in terawatt-hours (TWh), providing a standardized way to compare different energy sources.
Oil, Coal, Traditional biomass, Nuclear, Hydropower, Wind, Solar, Modern biofuels, Other renewables: These categories represent various sources contributing to global energy consumption.
: Approximate total global primary energy consumption.
Oil Exploration / Production
Oil Rig Drilling: Extracting crude oil from underground reservoirs using drilling technology.
Seismic Surveys: Using seismic waves to create images of subsurface geological structures and identify potential oil reservoirs.
U.S. Greenhouse Gas Emissions in 2019
*Economic Sectors:
* Transportation (29%): Emissions from vehicles, aircraft, and other transportation modes.
* Electricity Generation (25%): Emissions from power plants burning fossil fuels.
* Industry (23%): Emissions from industrial processes, such as manufacturing and chemical production.
* Agriculture (10%): Emissions from agricultural activities, including livestock and crop production.
* Commercial (7%): Emissions from commercial buildings and operations.
* Residential (6%): Emissions from residential buildings, primarily from heating and cooling.
Gases:
Carbon Dioxide (80%): The most significant greenhouse gas, mainly from burning fossil fuels.
Methane (10%): A potent greenhouse gas, emitted from natural gas and agricultural activities.
Nitrous Oxide (7%): A greenhouse gas emitted from agricultural and industrial activities.
Fluorinated Gases (3%): Synthetic greenhouse gases used in various industrial applications.
The Extra Cost of Using Nonrenewables: Acid Rain
, : Chemical formulas for sulfuric acid and nitric acid, the primary components of acid rain.
, , : These compounds are precursors to acid rain, formed from emissions of nitrogen oxides and sulfur dioxide.
Mineral and Raw Material Resources
Annual U.S. consumption (Gt) includes:
Stone, sand, gravel: Used in construction and infrastructure projects.
Industrial minerals: Minerals used in various industrial applications, such as fertilizers and ceramics.
Metals: Used in manufacturing, construction, and electronics.
Nonrenewable organics: Fossil fuels used for energy and manufacturing.
Agricultural, fishery, and forestry products: Resources from agriculture, fishing, and forestry sectors.
Increasing Prices of Metal Resources
Iron Ore Price (USD/Pound): Tracks the cost of iron ore, an essential raw material for steel production.
Copper Price (USD/Pound): Monitors the cost of copper, a widely used metal in electrical and construction applications.
The Cost of Resource Exploration
South Africa Mine dumps: Illustrates the environmental impact of mining activities and the accumulation of waste materials.
Water Resources
Water is a vital resource to all life and will continue to be a valuable resource, essential for drinking, agriculture, and industry.
Lake Powell, Utah: Drought lowers lake level, demonstrating the vulnerability of water resources to climate change and overuse.
Groundwater: An Example
Ogallala aquifer supplies much of the southern Great Plains with fresh water, supporting agriculture and communities in the region.
Thought Questions
Can you think of any environmental costs of the resources that you use? Consider pollution, habitat destruction, and resource depletion.
Are there any resources that you use that you did not know were associated with geology? Reflect on the origin of everyday items and their connection to Earth resources.
What Earth resources do you use in your everyday life? List the resources you consume and how they are used.
Natural Hazards
Geologists seek to understand Earth processes well enough to predict NATURAL HAZARDS and evaluate their risks to society, enabling better preparedness and mitigation efforts.
Examples:
End of Cretaceous asteroid impact: A massive impact event that caused widespread extinction.
Hurricanes: Tropical cyclones that bring strong winds, heavy rain, and storm surges.
Flooding: Overflow of water onto land that is normally dry.
Earthquakes: Sudden release of energy in the Earth's crust that creates seismic waves.
Volcanoes: Openings in the Earth's crust through which molten rock, gases, and ash erupt.
Landslides: Movement of rock, soil, or debris down a slope.
Bolides: Large meteors that explode in the atmosphere.
California Area Earthquake Probabilities
Magnitude 6.7: >99% (30-Year Probability): High likelihood of an earthquake of this magnitude occurring in the next 30 years.
Magnitude 7.0: 94% (30-Year Probability): Significant chance of a major earthquake in the near future.
Magnitude 7.5: 46% (30-Year Probability): Moderate probability of a severe earthquake.
Magnitude 8.0: 4% (30-Year Probability): Low but non-negligible risk of a great earthquake.
Probabilities do not include the Cascadia Subduction Zone, which could produce even larger earthquakes.
Thought Questions
What happened in this image? Analyze a provided image to identify geological events or hazards.
How can this example be used to help you make an educated decision about purchasing a home? Consider geological risks when making real estate decisions.
Environmental and Global Change
Humans have had a profound impact on Earth’s environment for thousands of years, leading to significant alterations in ecosystems and climate.
Antarctic stratospheric ozone hole: Depletion of the ozone layer due to human-produced chemicals.
Effects of acid rain: Damage to ecosystems and infrastructure due to acidic precipitation.
Global Climate Change
Global surface warming (°C) has been observed and predicted, indicating a clear trend of rising temperatures worldwide.
Observed twentieth-century warming and predicted twenty-first-century warming: Data showing past and future temperature increases.
Thought Question
What part of your life is affected by the work of geologists? Think about how geology influences resource availability, hazard management, and environmental policies.
Key Terms and Concepts Module 1
Acid rain: Precipitation that is made acidic by atmospheric pollution.
Anthropogenic: Resulting from or influenced by human activity.
Aquifer: An underground layer of permeable rock or sediment that holds water.
Biosphere: The regions of the surface, atmosphere, and hydrosphere of the earth (or analogous parts of other planets) occupied by living organisms.
Bolide: A large meteor that explodes in the atmosphere.
Earthquake: A sudden and violent shaking of the ground, sometimes causing great destruction, as a result of movements within the earth's crust or volcanic action.
Environment: The surroundings or conditions in which a person, animal, or plant lives or operates.
Flood: An overflow of a large amount of water beyond its normal limits, especially over what is normally dry land.
Fossil fuel: A natural fuel such as coal or gas, formed in the geological past from the remains of living organisms.
Geology: The study of the structure of the earth and its rocks, and of the processes that form them.
Global change: Planetary-scale changes in the Earth system, including climate change, ozone depletion, and land degradation.
Greenhouse gas: A gas that contributes to the greenhouse effect by absorbing infrared radiation.
Groundwater: Water held underground in the soil or in pores and crevices in rock.
Hurricane: A tropical cyclone with sustained winds of 74 miles per hour or greater.
Landslide: The sliding down of a mass of earth or rock from a mountain or cliff.
Natural hazards: A natural event such as a flood, earthquake, or hurricane that causes great damage or loss of life.
Natural resources: Materials or substances such as minerals, forests, water, and fertile land that occur in nature and can be used for economic gain.
Nonrenewable resource: A resource of economic value that cannot be readily replaced by natural means on a level equal to its consumption.
Renewable resource: A resource that can be replenished naturally over a relatively short period of time.
Module 2: How We Study Earth
The Scientific Method
A procedure used to discover how the universe works through systematic observations and experiments, ensuring that conclusions are based on evidence and rigorous testing.
Steps:
Initial Observation: Noticing a phenomenon or problem that needs explanation.
Hypothesis: Formulating a testable explanation for the observation.
Test: Conducting experiments or collecting data to evaluate the hypothesis.
Revised Hypothesis: Modifying the hypothesis based on the results of testing.
Prediction: Making specific statements about what should occur if the hypothesis is correct.
Geoguesser - an example of hypothesis formation and testing, where observations and iterative guesses lead to a conclusion.
Thought Questions
At a fundamental level we all use the scientific method in our every day lives, often without realizing it.
Provide an example of how you have utilized this systematic approach to address a problem in your life, illustrating the practical application of the scientific method.
Science of Geology
Geologists utilize the scientific method in order to understand Earth processes and history:
In the field: Collecting data and making observations in natural settings.
In the laboratory: Performing experiments and analyzing samples to understand Earth materials and processes.
Science of Geology: Disciplines
Geoscience: An umbrella term for all sciences related to the Earth.
Geology: The study of the Earth's physical structure and substance, its history, and the processes that act on it.
Geophysics: The study of the Earth's physical properties and processes using physics.
Geochemistry: The study of the chemical composition and processes of the Earth.
Geobiology: The study of the interactions between the Earth and its biosphere.
Principle of Uniformitarianism
Processes that occur on modern Earth have worked in much the same way during the geologic past (James Hutton), allowing scientists to interpret ancient events based on present-day observations.
“The present is the key to the past.” (Charles Lyell): This phrase encapsulates the idea that current processes can explain past events.
Allows geologists to interpret Earth’s geologic record by assuming that the same physical and chemical laws have operated throughout time.
Physics and chemistry Principles
Physics and chemistry the same today as in past, underpinning the predictability and understanding of Earth processes.
Rates of Earth Processes: Slow to Fast
Over millions of years, layers of sediments built up over the oldest rocks. The most recent layer-the top-is about 250 million years old.
*The rocks at the bottom of the Grand Canyon are 1.7-2.0 billion years old.
About 50,000 years ago, the explosive impact of a meteorite (perhaps weighing 300,000 tons) created this 1.2-km-wide crater in just a few seconds, demonstrating the range of time scales in geological processes.
Rates of Earth Processes
Typical lab conditions, Strain rate : This formula represents the rate at which materials deform under stress.
*Shear strain rate regimes
Processes to Products: Geological processes, from slow sedimentation to rapid meteorite impacts, produce a wide range of geological features.
Meet Planet Earth: The Surface
Himalaya: A major mountain range formed by the collision of tectonic plates.
Marianas Trench: The deepest part of the world's oceans, formed by subduction.
Topography and Bathymetry: The study of the Earth’s surface and underwater features.
Mt. Everest: The highest point on Earth.
Typical elevation of land surface is 0-1 km.
Challenger Deep: The deepest known point in the ocean.
Typical depth of ocean is 4-5 km.
Meet Planet Earth: The Interior
A Layered Earth: The Earth consists of distinct layers with varying compositions and properties.
Crust (0-40 km): 0.4% of Earth's mass: The outermost solid layer of the Earth.
Mantle (40-2890 km): 67.1% of Earth's mass: The thickest layer of the Earth, composed mainly of silicate rocks.
Liquid iron outer core (2890-5150 km): 30.8% of Earth's mass: A liquid layer composed mainly of iron and nickel.
Solid iron inner core (5150-6370 km): 1.7% of Earth's mass Density variations throughout: A solid sphere composed mainly of iron and nickel.
The Inner Core
Primarily IRON and NICKEL: The main components of the inner core.
Solid: Due to immense pressure.
The Outer Core
Primarily IRON and NICKEL with sulfur and oxygen: The chemical composition of the outer core.
Liquid: Allowing for convection currents that generate Earth's magnetic field.
The Mantle
Primarily SILICATES (silicon and oxygen) with abundant magnesium: The primary minerals in the mantle.
Plastic-like solid: Able to flow slowly over long periods.
The Crust
Primarily SILICATES (silicon and oxygen) with abundant aluminum: The main components of the crust.
Rigid solid: The solid outermost layer of the Earth.
The Crust: Two Varieties
Continental vs. Oceanic Crust Less dense continental crust floats on denser mantle: Differences in density and composition between continental and oceanic crust.
Continental crust is less dense and thicker than oceanic crust and therefore rides higher, leading to the formation of continents.
Thought Question
The continental crust, upon which we live, has an average density of 2.8g/cc. At the end of the eighteenth century, Henry Cavendish calculated that the average density for Earth is 5.5g/cc. How does your understanding of the internal structure of our planet explain this discrepancy? The denser core and mantle contribute to the overall higher average density of the Earth.
Earth as a System
Open system: Exchange energy and mass, allowing for interactions between different components of the Earth system.
Three primary sources of energy: Solar, trapped, radioactivity Open and interacting geosystems: Energy sources that drive Earth’s processes.
Positive and negative feedbacks between the systems, regulating and influencing Earth’s climate and geological activity.
Climate System
Earth’s climate is variable and is influenced by many components of the Earth system, including the atmosphere, oceans, and land surfaces.
Plate Tectonic System
Convection in the mantle drives the movement of Earth’s surficial plates, leading to the formation of mountains, volcanoes, and earthquakes.
Note: Plates are composed of lithosphere, which is the crust and upper, rigid mantle.
Geodynamo System
Magnetic field generated by convection in the outer core, protecting the Earth from harmful solar radiation.
Magnetic reversals have occurred in the past, providing evidence of the dynamic nature of the Earth's interior.
Thought Question
Explain how an increase in heat flux and associated increased mantle convection would influence both the plate tectonic and climate systems. Increased convection could lead to more frequent volcanic activity and changes in plate movement, impacting climate and geological processes.
Geologic Time and Earth Systems
Key events timeline: Earth and planets form, moon forms, oldest lunar rocks, evidence of erosion by water, fossils of primitive bacteria, etc., providing a chronological framework for understanding Earth’s history.
Key Terms and Concepts
Asthenosphere: The ductile part of the upper mantle just below the lithosphere, allowing for plate movement.
Climate: The long-term average of weather conditions in a region.
Climate system: All parts of the Earth system and their interactions that determine climate.
Core: The central part of the Earth, composed mainly of iron and nickel.
Crust: The outermost solid layer of the Earth.
Earth system: All of the interacting physical, chemical, and biological processes on Earth.
Fossil: The remains or impression of a prehistoric organism preserved in petrified form or as a mold or cast in rock.
Geodynamo: The process by which Earth generates its magnetic field through convection in the outer core.
Geologic record: The information preserved in rocks that documents Earth's history.
Geosystem: A system of interacting geological elements and processes.
Hypothesis: A testable explanation for a phenomenon.
Inner core: The solid central part of the Earth.
Lithosphere: The rigid outer layer of the Earth, consisting of the crust and upper mantle.
Magnetic field: A field of force surrounding a magnetic object or moving electric charge.
Mantle: The layer of the Earth between the crust and the core.
Outer core: The liquid layer surrounding the inner core.
Plate tectonic system: The theory that the Earth's lithosphere is divided into plates that move and interact at their boundaries.
Principle of uniformitarianism: The idea that the same geological processes operating today operated in the past.
Scientific method: A systematic approach to discovering how the universe works through observation and experimentation.
Seismic wave: An elastic shock wave that travels through the Earth.
topography: he arrangement of the natural and artificial physical features of an area.
Module 3: Plate Tectonics: The Unifying Theory of Geology
Discovery of Plate Tectonics
Alfred Wegener (1915) proposed that all of the continents were once part of a large supercontinent – Pangaea, based on multiple lines of evidence.
Similarities in shorelines: The coastlines of continents, such as South America and Africa, appear to fit together.
Terrestrial geologic evidence: Similar rock formations and mountain ranges found on different continents.
Distinctive fossil groups found in Africa and South America: Fossils of the same species found on widely separated continents suggest they were once connected.
Paleontological Evidence
No mechanism to transport across ocean: The absence of a plausible explanation for how species could have crossed vast oceans.
Divergence of species following break-up: The evolution of distinct species on different continents after they separated.
Problems with Continental Drift
Wegener proposed a mechanism for drift: Continents plowed through solid ocean floor, Tidal forces drove the motion,
Tidal forces are know to be too weak to move continents.
However, the hypothesis was largely rejected due to an inadequate mechanism of continental movement, as Wegener's proposed mechanisms were physically impossible.
Seafloor Spreading
Original evidence for continental drift was from continental rocks, but lacked a viable mechanism.
Technological advances in the 1940s, 1950s, and 1960s allowed investigation of the seafloor, providing new insights into Earth's dynamics.
New data provided intriguing new information!
Geology of the Ocean Floor
Bathymetry of the ocean basins: Sonar revealed ridge system in ocean basins. Ridge system is continuous around the entire globe. There is a central RIFT VALLEY within the ridge.
The Ocean Floor & Seafloor Spreading
Hess and Dietz propose “seafloor spreading” hypothesis in which new crust is formed as older crust separates along rifts associated with mid-ocean ridges, providing a mechanism for continental drift.
Recycling of seafloor was proposed at margins of the Pacific through subduction, balancing the creation of new crust at mid-ocean ridges.
Thought Questions
What can you say about the RATE of new seafloor production as compared to the RATE of seafloor recycling? What ramifications does your answer have with respect to the size of our planet? The rates are approximately equal, maintaining a constant surface area of the Earth.
Seafloor Spreading: Testing the Hypothesis
The “seafloor spreading” hypothesis presents a testable hypothesis in which seafloor adjacent to the ridges should be younger than the seafloor far away from the ridges, and that the ages should be symmetric on either side of the ridges.
Vine and Matthews (1963) tested this hypothesis using magnetism.
Magnetic polarity reversals are recorded in ocean floor basalt: Magma cools, forming new crust. Polarity at time of cooling is preserved. Old crust is pushed aside.
Normal and Reversed Magnetic Polarity
Geographic north / Magnetic north: The Earth's magnetic field periodically reverses, with the magnetic north pole becoming the magnetic south pole and vice versa.
Seafloor Ages Support the Seafloor Spreading Hypothesis
Younger rocks are found closer to the ridge, supporting the idea that new crust is formed at mid-ocean ridges.
Spreading history can be reconstructed by knowing the ages of the seafloor, providing a record of plate movements over millions of years.
Plate Tectonic Theory
The surface of Earth (lithosphere) is divided into individual hard, continuous shells called plates, which includes both the crust and the uppermost part of the mantle.
The plates move about, with deformation confined to the boundaries of plates, where most geological activity occurs.
Plate Tectonic Theory: Plate Boundaries
Divergent boundaries: plates move apart and create new lithosphere, typically at mid-ocean ridges.
Convergent boundaries: plates move together, oceanic lithosphere is recycled back into the mantle, continental plates are deformed, leading to mountain building.
Transform-fault boundaries: plates slide horizontally past each other, causing earthquakes.
All plate boundaries have earthquakes: Resulting from the movement and interaction of plates.
Volcanoes mostly at divergent and convergent boundaries: Where magma can rise to the surface.
Divergent Boundaries
Two varieties:
Oceanic plate separation Mature: Example - Mid-Atlantic Ridge.
Continental plate separation Juvenile: Example - East African Rift Valley.
Divergent Boundaries (Continental)
Early stages of divergence
Continental rifting will lead to a break-up of continents and the formation of new oceans.
Shallow earthquake focus depths As oceanic lithosphere spreads apart, new seafloor is created through volcanic processes.
Divergent Boundaries (Oceanic)
Ocean basin gradually grows as volume of oceanic crust increases.
*Shallow earthquake focus depths
*Decompression melting
Convergent Boundaries
Three varieties:
Ocean – Ocean convergence Subduction: Example - Mariana Islands.
Ocean – Continent convergence Subduction: Example - Andes Mountains.
Continent – Continent convergence Collision: Example - Himalaya Mountains.
Convergent Boundaries (Ocean - Ocean)
Subduction (recycling) of denser oceanic plate
Volcanic island arc forms on non-subducting plate.
Earthquake focus depths range from shallow to deep
Convergent Boundaries (Ocean - Continent)
Subduction (recycling) of oceanic plate
Volcanic mountain belt forms on continent.
Earthquake focus depths range from shallow to deep
Convergent Boundaries (Continent - Continent)
Continental lithosphere cannot recycle.
Over-thickening of lithosphere and large mountain ranges result.
Severe earthquakes Volcanic arc
Transform Fault Boundaries
Two varieties:
Mid-ocean ridge transform fault: Connect segments of mid-ocean ridges.
Continental transform fault: Example - San Andreas Fault.
Mid-ocean Ridge Transform
Due to the spherical nature of Earth, divergent boundaries are broken with a step-like pattern, resulting in transform motion.
Continental Transforms
At transform faults, plates slip horizontally past each other.
Plate Tectonics World Map
Convergent, Divergent, Transform Boundaries listed.
Organizing Our Thoughts about Plate Boundaries
New plate made or destroyed? Consider whether the boundary is constructive or destructive.
Volcanoes? Identify the presence or absence of volcanic activity.
Big, small, shallow, and/or deep earthquakes? Characterize the seismic activity at the boundary.
Between what types of crust? Determine whether the boundary involves oceanic, continental, or both types of crust.
How Fast Do the Plates Move?
Typical relative plate velocities are between 5-150 mm/year, varying based on the driving forces and resistance at plate boundaries.
Velocity = Distance /Time
Method #1: Seafloor Ages
Distance: Scale bar is used to determine distance between isochrons.
Time: Magnetic anomalies are used to determine age.
Velocity = Distance /Time
Method #2: Mantle Plumes and Hotspots
Mantle plumes act as fixed reference points, allowing for the measurement of plate movement relative to these stationary features.
Distance: Scale bar is used to determine distance between volcanoes/islands.
Time: Volcanic rocks are dated radiometrically.
Velocity = Distance /Time
Method #3: Global Positioning System
GPS satellites are used to determine precise location of instrument through triangulation.
*By measuring one location continuously, the distance moved over the time of measurement can be determined.
Velocity = Distance /Time
What Drives the Plates?
Internal heat and associated density differences drive plate motion through:
Mantle convection: The primary driving force, with hotter material rising and cooler material sinking.
Ridge push: The force exerted by the elevated mid-ocean ridge pushing plates away from it.
Slab pull: The force exerted by the sinking of a cold, dense oceanic plate into the mantle.
Thought Question
We spent time earlier in this lesson discussing Earth’s magnetic field and its reversals through time.
*What do you predict would happen to plate motions on Earth if the magnetic field shut down? Why? It is unlikely to impact plate motion. The magnetic field is generated deep within the Earth and has no direct impact.
Reconstructing Plate Motion
The assembly and break-up of Pangaea, illustrating the dynamic nature of continental configurations over geological time scales.
An introduction to the Wilson Cycle of supercontinents, describing the cyclical process of supercontinent formation and breakup.
Key Terms and Concepts
Continental drift
*Convergent boundary
Divergent boundary
Island arc
Isochron
Magnetic anomaly
Magnetic time scale
Pangaea
Plate tectonics
Rodinia
Seafloor spreading
Spreading center
Subduction
Transform fault