Earth's Interior and Plate Tectonics
Unit 4 Practice Test Notes
1. Earth's Interior Layers
Pie Slice Illustration: Draw a pie slice to visually represent and label the major layers of Earth's interior, which include:
Crust
Mantle
Outer Core
Inner Core
2. Major Features of Earth's Layers
Crust: A Thin and solid layer, differentiated into oceanic and continental crust.
Mantle: A Thick layer composed of semi-solid rock that flows slowly, allowing tectonic plates to move.
Outer Core: Liquid iron and nickel, responsible for Earth's magnetic field.
Inner Core: Solid iron and nickel, extremely high pressure and temperature.
3. Differences Between Oceanic and Continental Crust
Oceanic Crust:
Thinner (about 7 km)
Denser (composition mainly of basalt)
Younger (a few million years old)
Continental Crust:
Thicker (up to 70 km)
Less dense (composition mainly of granite)
Older (up to billions of years old)
4. Temperature and Pressure in Earth's Layers
Temperature and Pressure Influence:
As depth increases in Earth, both temperature and pressure increase, affecting the physical state of materials.
Crust: Solid due to low temperature and pressure.
Mantle: Semi-solid (asthenosphere) capable of flow due to increasing temperature and pressure.
Outer Core: Liquid state due to high temperatures,
Inner Core: Solid due to immense pressure despite high temperatures.
5. Types of Seismic Waves and S-P Time Calculation
Types of Seismic Waves in Seismogram:
P-Waves (Primary Waves): Compressional waves that travel through solids and liquids.
S-Waves (Secondary Waves): Shear waves that only travel through solids.
S-P Time Calculation: Measure the difference in arrival times of P-waves and S-waves to determine the distance to the earthquake epicenter.
6. Characteristics of Seismic Waves
P-Waves:
Fastest seismic waves.
Travel through both liquids and solids.
Particle motion is parallel to wave direction.
S-Waves:
Slower than P-waves.
Only travel through solids.
Particle motion is perpendicular to wave direction.
7. S-Wave and P-Wave Shadow Zones
Shadow Zones:
P-Wave Shadow Zone: Zone where no P-waves are detected, indicating the presence of liquid outer core.
S-Wave Shadow Zone: Zone where S-waves do not arrive, confirming the liquid nature of the outer core.
8. Convection in the Mantle and Mid-Ocean Ridge
Sketch and Label: Illustrate how convection currents in the mantle lead to the formation of mid-ocean ridges, where tectonic plates diverge, causing magma to rise and form new crust.
9. Evidence for Seafloor Spreading
Five Major Pieces of Evidence:
Mid-Ocean Ridges
Age of Seafloor
Ocean Floor Sediments
Magnetic Reversal Patterns
Fossil Distribution
10. Magnetic Reversals and Seafloor Spreading
Geomagnetic Reversals:
Occur over geological time scales, leaving patterns on either side of mid-ocean ridges that mirror each other, suggesting seafloor spreading.
Sketch: Include a diagram showing the magnetic patterns on opposite sides of a ridge.
11. Thickness of Seafloor Sediments
Evidence of Seafloor Spreading: Thickness of sediments increases with distance from mid-ocean ridges; thinner sediments indicate younger seafloor, while thicker sediments indicate older seafloor.
Sketch: Illustrate sediment thickness in relation to distance from mid-ocean ridges.
12. Rate of Seafloor Spreading Calculation
Average Rate: Calculate the average rate of seafloor spreading over the past 3 million years by measuring the distance between features on the ocean floor and dividing by time (in years).
Formula:
Rate = \frac{Distance}{Time} \text{ in centimeters/year}
13. Glacial Striations and Pangea
Glacial Striations: Evidence from scratches left by glaciers that show historical movement directions, supporting the theory of continental drift.
14. Major Types of Plate Boundaries
Three Major Types:
Divergent Boundaries: Plates move apart, creating new crust (e.g., Mid-Atlantic Ridge).
Convergent Boundaries: Plates collide or move toward each other, leading to subduction or mountain formation (e.g., Himalayas).
Transform Boundaries: Plates slide past each other, causing earthquakes (e.g., San Andreas Fault).
15. Specific Examples of Plate Boundaries
Continental Divergent: East African Rift.
Oceanic Divergent: Mid-Atlantic Ridge.
Transform: San Andreas Fault.
Oceanic-Oceanic Convergent: Aleutian Trench.
Oceanic-Continental Convergent: Cascadia Subduction Zone.
Continental-Continental Convergent: Himalayas.
16. Sketch of Subduction Zone
Identify and label features: Illustrate what happens at a subduction zone where an oceanic plate dives beneath a continental plate, producing trenches and volcanic activity.
17. Latitude and Longitude Locations
Galapagos Hot Spot: Approximately 0°N, 90°W.
Iceland Hot Spot: Approximately 64°N, 18°W.
Sandwich Plate: Approximately 55°S, 38°W.
18. Geologic Activity Prediction at Tonga Trench
Tonga Trench: Expected high tectonic activity, including earthquakes and volcanic events due to subduction processes at coordinates 20°S, 173°W. Investigate nearby plate boundaries for further features and events.
19. Other important stuff not on the study guide
Structural Layers of the Earth: The Earth's structural layers, defined by their physical properties, comprise the Lithosphere, Asthenosphere, Mesosphere, Outer Core, and Inner Core.
Which layer has Iron and Nickel? Both the Outer Core (liquid iron and nickel) and the Inner Core (solid iron and nickel) contain iron and nickel.
Which creates the North and South poles? The Outer Core is responsible for generating Earth's magnetic field, which creates the North and South poles.
Oceanic versus Continental crust?
Which is basaltic? Oceanic crust is basaltic in composition.
Which is granitic? Continental crust is granitic in composition.
What are the differences between age, density, and thickness?
Oceanic Crust: Thinner (about 7 km7 km), denser, and younger (a few million years old).
Continental Crust: Thicker (up to 70 km70 km), less dense, and older (up to billions of years old).
Seismic waves - which arrive first? Which arrives second? Which arrives last?
First: P-Waves (Primary Waves)
Second: S-Waves (Secondary Waves)
Last: Surface Waves (e.g., Love and Rayleigh waves)
Primary waves can travel through which layers of the Earth? What is the shadow zone?
Primary Waves (P-waves) can travel through all layers of the Earth: solids (crust, mantle, inner core) and liquids (outer core).
The P-Wave Shadow Zone is a zone on the Earth's surface, roughly between 103103 and 142142 degrees from an earthquake's epicenter, where no P-waves are directly detected. This is caused by the refraction of P-waves as they pass through the liquid outer core, bending away from this zone.
Secondary waves can travel through which layers of the Earth? What is the shadow zone?
Secondary Waves (S-waves) can only travel through solid layers of the Earth: the crust, mantle, and inner core.
The S-Wave Shadow Zone is much larger, encompassing all areas more than 103103 degrees from an earthquake's epicenter, where S-waves are not detected. This confirms the liquid nature of the outer core, as S-waves cannot travel through liquids.
What is the difference between the focus and epicenter of an earthquake?
The Focus (Hypocenter) is the exact point within the Earth where an earthquake originates or where the seismic rupture first occurs.
The Epicenter is the point on the Earth's surface directly above the earthquake's focus. This is the location often cited when reporting an earthquake.
How do alternating, symmetric black and white zones from an oceanic ridge show geomagnetic reversal?
Alternating, symmetric black and white zones from an oceanic ridge show geomagnetic reversal because, as new oceanic crust forms at the mid-ocean ridge, it records the Earth's magnetic field at that time. These patterns appear as alternating magnetic stripes of normal and reversed polarity on either side of the ridge. The symmetry of these patterns, mirroring each other away from the ridge, provides strong evidence for seafloor spreading and the occurrence of past geomagnetic reversals over geological time scales.