Earth's Composition & Mechanical Layers

• The Earth has distinct layers classified by composition and mechanical properties.

Earth's Layers by Composition

• Crust: Solid outer layer made of mainly Silicon, Oxygen, and Aluminum.
• Mantle: Ductile solid beneath the crust, consisting of Silicon, Oxygen, and Magnesium.
• Outer Core: Liquid layer made of primarily Nickel and Iron.
• Inner Core: Solid layer due to high pressure, also made of Nickel and Iron.
• Overall Composition: Oxygen (30%), Iron (35%), Silicon (15%), Magnesium (10%), and other elements (10%).

Earth's Layers by Mechanical Properties

• Lithosphere: The solid and brittle crust and upper mantle, broken into tectonic plates.
• Asthenosphere: The ductile upper mantle where tectonic plates float.

Tectonic Plates

• Continental Crust: Less dense, thicker, consists mainly of granite with oldest parts around ~4 billion years old.
• Oceanic Crust: More dense, thinner, primarily basalt which is recycled and subducts, with its oldest parts around ~200 million years old.

Plate Boundaries

• Plate boundaries include divergent, convergent, and transform types.

Types of Plate Boundaries

• Divergent: Plates move apart, creating new crust through mid-ocean ridges and rift valleys.
• Convergent: Plates move towards each other in several forms.
• Oceanic-Continental: Oceanic plate subducts, forming ocean trenches and volcanic arcs.
• Oceanic-Oceanic: Older oceanic plate subducts, creating ocean trenches and volcanic island arcs.
• Continental-Continental: No subduction, creating mountain ranges such as the Himalayas.
• Transform: Plates slide past each other, causing earthquakes without creating or destroying crust.

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 areas with earthquakes and volcanism, such as the West Coast of the USA.
• Passive Margins: Stable areas with low tectonic activity, such as the East Coast of the USA.

Examples of Features

• Convergent Boundaries: Aleutian & Mariana Islands (Oceanic-Oceanic), Himalayas & Alps (Continental-Continental), Andes (Oceanic-Continental).
• Divergent Boundaries: Mid-Atlantic Ridge, East African Rift.
• Transform Boundaries: San Andreas Fault, Alpine Fault. Oceanic crust subducts at convergent boundaries; volcanic activity occurs at oceanic-continental boundaries but not at continental-continental boundaries.

Faults

• Faults are fractures in Earth's crust where movement occurred.
• Earthquakes happen when seismic waves are released from blocks of crust slipping past each other.

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 above the hypocenter.
• Hypocenter: Underground starting point of the earthquake.

Faults and Plate Boundaries

• Form seismic activity areas; can exist away from plates, for example, Charleston and the New Madrid Fault.

Types of Faults

• Normal Fault: Hanging wall slides down, caused by tension, such as the East African Rift.
• Reverse Fault: Hanging wall slides up, caused by compression, such as the Rocky Mountains.
• Strike-Slip Fault: Horizontal movement without vertical movement, such as the San Andreas Fault.

Earthquake Fundamentals

• Earthquakes are caused by friction between tectonic plates causing energy buildup and release.

Magnitude of Earthquakes

• Magnitude: Intensity or "size" of an earthquake, influenced by rock rigidity and fault movement, with each magnitude increase representing an earthquake 10 times stronger. Richter Scale: Developed by Charles Richter in the 1930s; measures magnitude via ground motion (limited in 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: Measures damage and perception based on reported effects, ranging from not felt (I) to total destruction (XII).

Types of Seismic Waves

• Body Waves: Consist of P-waves (fastest, travel through solid and liquid) and S-waves (slower, travel only through solids).
• Surface Waves: Cause the most damage depending on depth, with shallower quakes causing more surface damage.

Measuring Earthquakes

• Seismographs record seismic waves, visualized by seismograms; P-waves arrive first, with 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

• Earth's timeline is categorized by eons, eras, periods, and epochs, with significant indicators such as orogeny (mountain building) and extinction events.
• Past climates are studied through proxies like ice cores, pollen grains, sediments, tree rings, corals, historical data, and fossils.

Precambrian Era (4.6 bya - 541 mya)

• Most of Earth's history; origin of Earth and life (cyanobacteria).

Paleozoic Era (541 mya - 251 mya)

• Age of Fish marked by geological events, major life diversification (Cambrian Explosion), and the Permian extinction.

Mesozoic Era (251 mya - 65 mya)

• Age of Reptiles with major climate changes and the K-T extinction event.

Cenozoic Era (65 mya - present)

• Age of Mammals with climate changes impacting North Carolina and the emergence of modern mammals and human ancestors.

Volcanoes

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

Classification of Volcanoes

• Active: Erupted historically, about 500 active volcanoes with 5-10 eruptions per 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 magma leads to explosive eruptions.
• Low Viscosity: Thin magma leads to effusive eruptions. Magma Types: Rhyolitic (most explosive), Andesitic (intermediate), and Basaltic (least explosive).

Pyroclastic Material

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

Types of Volcanoes

• Composite Volcanoes: Tall, layered structures with dangerous eruptions (e.g., Mt. Hood).
• Shield Volcanoes: Gently sloping, large volcanoes, primarily basaltic lava with less explosive eruptions.
• Cinder Cones: Small, steep-sided volcanoes formed from cinders, often with significant gas release (e.g., Paricutin).

Calderas

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

Deadliest Result of Volcanic Eruptions

• Ash blocks sunlight, leading to plant death and potential famine, such as The Year Without Summer.