Untitled document

Earth's Layers

• Earth's Layers Overview

  • The Earth consists of distinct layers classified by composition and mechanical properties:

    • Crust: Solid outer layer, composed mainly of Silicon (Si), Oxygen (O), and Aluminum (Al).

    • Mantle: Ductile solid beneath the crust, consisting of Silicon (Si), Oxygen (O), and Magnesium (Mg).

    • Outer Core: Liquid layer made primarily of Nickel (Ni) and Iron (Fe).

    • Inner Core: Solid layer due to high pressure, made also of Nickel (Ni) and Iron (Fe).

• Composition:

  • Oxygen: 30.0%

  • Iron: 35.0%

  • Silicon: 15.0%

  • Magnesium: 10.0%

  • Other Elements: 10.0%

• Mechanical Properties:

  • Lithosphere: Crust and upper mantle, solid and brittle, broken into tectonic plates.

  • Asthenosphere: Upper mantle, ductile solid where tectonic plates float.

• Tectonic Plates:

  • Continental Crust: Less dense, thicker, mainly granite; oldest parts ~4 billion years.

  • Oceanic Crust: More dense, thinner, primarily basalt; often recycled and subducts; oldest parts ~200 million years.

Plate Boundaries

• Types of Plate Boundaries:

  • Divergent: Plates move apart, creating new crust (e.g., mid-ocean ridges, rift valleys).

  • Convergent: Plates move toward each other.

    • Oceanic-Continental: Oceanic subducts, forming ocean trenches and volcanic arcs.

    • Oceanic-Oceanic: Older oceanic plate subducts, leading to ocean trenches and volcanic island arcs.

    • Continental-Continental: No subduction occurs, resulting in the formation of mountain ranges (e.g., Himalayas).

  • Transform: Plates slide past each other, causing earthquakes without crust creation or destruction.

• Key Processes Driving Plate Movement:

  • Slab Pull: Weight of the subducting plate pulls the trailing slab.

  • Ridge Push: Elevated mid-ocean ridges push plates away due to gravity.

• Common Locations:

  • Active Margins: Tectonically active with earthquakes and volcanism (e.g., West Coast USA).

  • Passive Margins: Stable with low tectonic activity (e.g., East Coast USA).

• Examples of Features:

  • Convergent: Aleutian & Mariana Islands (O-O), Himalayas & Alps (C-C), Andes (O-C).

  • Divergent: Mid-Atlantic Ridge, East African Rift.

  • Transform: San Andreas Fault, Alpine Fault.

• Summary: Oceanic crust subducts at convergent boundaries; volcanic activity is present at oceanic-continental boundaries but absent at continental-continental boundaries.

Faults

• Faults: Fractures in the Earth's crust where movement has occurred.

• Earthquakes: Release of seismic waves from blocks of crust slipping past one another.

• Key Terminology:

  • Fault: Plane of movement between crust pieces.

  • Hypocenter (Focus): Point inside the crust where an earthquake originates.

  • Epicenter: Surface location directly above the hypocenter.

• Fault Diagram:

  • Fault Plane: Surface along which faulting occurs.

  • Epicenter: Surface point directly above the hypocenter.

  • Hypocenter: Underground starting point of the earthquake.

• Faults and Plate Boundaries: Form seismic activity areas; faults can exist away from plates (e.g., Charleston, New Madrid Fault).

• Types of Faults:

  • Normal Fault: Hanging wall slides down (tension), e.g., East African Rift.

  • Reverse Fault: Hanging wall slides up (compression), e.g., Rocky Mountains.

  • Strike-Slip Fault: Horizontal movement without vertical movement, e.g., San Andreas Fault.

• Earthquake Fundamentals:

  • Why Earthquakes Occur: Friction between tectonic plates causes energy to build up and eventually release, leading to ground shaking.

  • Magnitude of Earthquakes:

    • Magnitude: Intensity or "size" of an earthquake, influenced by rock rigidity and fault movement.

    • Each increase in magnitude represents an earthquake 10 times stronger than the previous one.

    • Richter Scale: Developed by Charles Richter in the 1930s; measures magnitude via ground motion (limited use today).

    • Moment Magnitude Scale: Current method for measuring intensity based on total fault movement, accurate across all magnitudes.

  • Intensity Measurement:

    • Modified Mercalli Intensity (MMI) Scale: Ranges from not felt (I) to total destruction (XII), assesses damage and perception based on reported effects.

Types of Seismic Waves

• Types of Seismic Waves:

  • Body Waves:

    • P-waves: Fastest, travel through both solid and liquid.

    • S-waves: Slower, travel only through solids.

  • Surface Waves: Cause the most damage; the extent of damage depends on depth—shallower quakes produce more surface damage.

• Measuring Earthquakes:

  • Instruments: Seismographs record seismic waves, while seismograms visualize them. P-waves arrive first, followed by surface waves showing higher magnitudes.

  • Triangulation: Requires three seismic stations to locate the earthquake's epicenter using P-wave and S-wave travel time differences.

Geologic History

• Geologic History Summary: Major events in Earth's history are grouped by era and category, without exact dates necessary.

  • Past climates are studied using proxies like ice cores, pollen grains, sediments, tree rings, corals, historical data, and fossils.

  • The best proxy depends on the age of the event, spanning from thousands to billions of years ago.

  • Earth's history is categorized into eons, eras, periods, and epochs, with significant indicators such as orogeny (mountain building) and extinction events.

• Eras:

  • Precambrian Era (4.6 billion years ago - 541 million years ago): Most of Earth's history; origin of Earth and life (e.g., cyanobacteria).

  • Paleozoic Era (541 million years ago - 251 million years ago): Age of Fish marked by geological events, major life diversification (Cambrian Explosion), and the Permian extinction.

  • Mesozoic Era (251 million years ago - 65 million years ago): Age of Reptiles with major climate changes and the K-T extinction event.

  • Cenozoic Era (65 million years ago - present): Age of Mammals, with climate changes impacting North Carolina and the emergence of modern mammals and human ancestors.

• Overall, Earth's timeline reflects significant geological and biological transformations throughout its history.

Volcanoes

• Definition: A volcano is an opening in the Earth's crust that allows lava, ash, and gases to escape.

• Classification of Volcanoes:

  • Active: Have erupted historically (~500 active, 5-10 eruptions/month).

  • Dormant: Not erupted in historical times but expected to erupt again.

  • Extinct: Unlikely to erupt again.

• Locations of Volcano Formation:

  • Divergent Boundaries: Tectonic plates move apart.

  • Convergent Boundaries: Plates push together.

  • Hot Spots: Magma rises from deep within the Earth.

• Viscosity of Magma:

  • High Viscosity: Thick, leads to explosive eruptions.

  • Low Viscosity: Thin, leads to effusive eruptions.

• Magma Types:

  • Rhyolitic: Most explosive.

  • Andesitic: Intermediate explosiveness.

  • Basaltic: Least explosive.

• Pyroclastic Material: Material ejected during eruptions includes pyroclastic flow, tephra, lava bombs, fire fountains, and various gases.

• Types of Volcanoes:

  1. Composite Volcanoes: Tall, layered structures; can produce dangerous eruptions (e.g., Mt. Hood).

  2. Shield Volcanoes: Gently sloping, large; primarily basaltic lava leading to less explosive eruptions.

  3. Cinder Cones: Small, steep-sided; formed from cinders, often with significant gas release (e.g., Paricutin).

• Calderas: Formed after large explosive eruptions; bowl-like depressions that can fill with lakes (e.g., Kilauea, Yellowstone).

• Deadliest Result of Volcanic Eruptions: Ash can block sunlight, leading to plant death and potential famine (e.g., The Year Without Summer).