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Inner Structure of the Earth
Inner Structure of the Earth
1. Inner Core—dense and solid
4000 miles below surface2. Outer Core—Molten or
liquid• Both are mostly hot and
made of hot metal (iron) • Appro 1,400 miles thick 3. Mantle—thick layer of
rock (1800 miles thick); mostly solid, but has pockets of magma (melted rock)
4. Crust—very thin layer; rocky surface
Below the oceans, the crust is about 2 miles thick. Below the continents it averages 75 miles in thickness.
Internal Forces that Shape Landforms
1. Volcanoes—form when magma inside the earth breaks through the crust. Lava flows and may produce a large, cone-shaped mountain
2. Fault—a break in the earth’s crust. Movement along a fault can send out shock waves, causing an earthquake.
The Big Burp
1. The lithosphere—the earth’s crust and upper layer of the mantle—are broken into a number of large, moving plates.
2. The plates slide very slowly over a hot, pliable layer of mantle.
3. The earth’s oceans and continents ride atop of the plates.
The Plate Tectonic Theory
Plate Boundary Features
The Ring of Fire
A circle of volcanic mountains that are surrounding the Pacific Plate
2. Hot Spots: hot regions deep within the mantle that produce magma, which rises to the surface. Volcanic island chains form as oceanic plates drift over the hot spot. Example: Hawaiian Islands.
What Happens When
Plates Meet?
Collision/Spreading Zones
• They collide and push slowly against each other and form a collision or converging zone.
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Convergent Plate Boundaries
Ocean - Continent
Ocean - Ocean
Continent-ContinentTasa Graphic Arts Inc.
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• If 2 continental plates collide, mountains are formed. Example: Himalayas
Converging (Collision) Zone
• If 2 oceanic plates collide, 1 slides under the other. Islands often form this way. Example: Japan
Subduction zone.*If an oceanic plate collides with a
continental plate, the heavier oceanic plate will slide under the lighter, continental plate. Results: volcanic mountain building and earthquakes.
South American Subduction
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Plates pull away from each other and form a spreading zone. These areas are likely to have earthquakes, volcanoes, and rift valleys (a large split along the crest of a mountain).
SPREADING ZONE
Red Sea Spreading Center
East African Rift Valley
National Geographic Society.
At a FAULT, the plates will grind or slide past each other rather than colliding. Example: San Andres Fault.
Fault
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San Andreas
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Weathering
• Breaks down rock at or near the earth’s surface into smaller pieces
Mechanical weathering
• rock is actually broken or weakened physically.
Mechanical weathering • Frost Wedging: most common
form; water freezes to ice in a crack (water expands 10% when frozen). Ice widens the crack and splits the rock.
Mechanical weathering• Seeds: Seeds will take root
and grow in the cracks of a rock. As the plant grows, the rock will split.
Chemical Weathering • Alters the rock’s
chemical make-up by changing the minerals that form the rock. Most important forces are water (H2O) and carbon dioxide (CO2).
H2O + CO2 + CaCO3 --> Ca+2 + 2HCO3-
Chemical Weathering • Carbonic Acid: CO2 from the air or soil
combines with H2O to make carbonic acid. When the acidic water seeps into the cracks in certain rocks (limestone) it dissolves the rocks away. Examples: caves
With the snow-draped Sierra Nevada as a backdrop, unique erosion formations called sand tufa stand like giant cauliflower stalks in a dry Arizona lake bed. Before this alkaline lake went dry, tufa formed when a freshwater spring percolated from below and formed calcium carbonate deposits. When the lake's level dropped, these fragile formations surfaced, and wind went to work removing the sand beneath the deposits.
Chemical weathering • Acid Rain: Chemicals in the
polluted water combine with water vapor and then fall back to the earth as acid rain.
• Acid Rain is known to be caused by industrial pollution, volcanic activity, and acid producing agents in the oceans.
A stand of withered red spruce and Fraser fir trees blights
a green vista in North Carolina's Mount Mitchell State Park.
Erosion• The movement of weathered
materials such as gravel, sand, and soil.
• An agent of mechanical weathering• Three common forms
–Wind–Water–Glaciers
Erosion—Wind
• Most damaging in areas that are dry and with few plants
• Wind-blown sand carves and/or smooths natural and man made formations
Desert winds sculpted these gentle swirls out of the limestone hills in Black Gap Wildlife Management Area, Texas. This remote, 100,000-acre (40,470-hectare) area in West Texas contains some
of the lowest, driest, and hottest areas in the Chihuahuan
Desert.
Erosion—Water
• Moving water carries sediment
• Grinds away rock like sandpaper
• Forms canyons and valleys
Erosion—Glaciers• Huge, slow moving sheets of ice• When melted, leave behind piles of
rock/debris called moraines• Great Lakes formed by glaciers
The Bernard Glacier in Alaska's Saint Elias Mountains looks like a huge alpine highway. Glaciers are slow but highly effective shapers of the land, essentially carrying away anything in their path—from soil and rocks to hills and even the sides of mountains.
