Download Inside the Earth Ch. 4 Section 1

The Structure of the Earth
Understanding the structure of the
Earth begins with an understanding of
how the Earth came to be…
Composition of Earth
Three Major Layers…
1. Crust
2. Mantle
3. Core (Includes inner core and outer core)
*Layers are made of different kinds of materials
Outermost layers: lightest, less dense materials
Innermost layers: densest materials
The Crust
• Outermost layer; thinnest; layer we live on
Two types:
1. Contintental – composition similar to
granite; about 25 miles thick beneath
continents; not as dense as oceanic crust
2. Oceanic – composition similar to basalt;
about 6.5 miles thick beneath ocean;
denser than granite
• Known as the lithosphere: “rock sphere”
• Made of tectonic plates
The Crust
• Layer we know the most about
• Made of mixture of elements
• 8 most common elements in Earth’s crust
by mass:
46.6% Oxygen (O) 3.6% Calcium (Ca)
27.7% Silica (Si)
2.8% Sodium (Na)
8.1% Aluminum (Al) 2.6% Potassium (K)
5.0% Iron (Fe)
2.1% Magnesium (Mg)
Diagram: Inside the Earth
The Mantle
• Layer between the crust and the core
 Asthenosphere: upper mantle; layer of weakened
rock between crust and mantle; means “weak sphere”
• Extremely thick; 2/3 of the Earth’s mass
• No one has ever seen this layer; observations made
from surface (volcanoes/lava)
• Made of almost solid rock (magma), flows slowly
like thick tar or fudge
• Also known as the mesosphere
The Core
• Two regions: outer and inner core
• Extremely hot; under great pressure
Outer Core: liquid iron; generates a magnetic
field
Inner core: solid iron; some nickel; pressure
so great it cannot melt, atoms vibrate in
place, radiation adds to temperature
Scientific Physical Layers
Compositional Layers:
• Crust
• Mantle
• Core
Mechanical/Structural Layers
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–
–
–
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Lithosphere (Crust/Uppermost mantle, hardened rock
Asthenosphere (Upper Mantle)
Mesosphere (Mantle)
Outer core
Inner core
Review!
Layers You Need to Know
• Lithosphere (uppermost mantle): “rock sphere”;
tectonic plates
• Asthenosphere (upper mantle): “weak sphere”;
soft layer, thick flowing molten rock; pieces of
crust move on this layer
• Mesosphere (mantle): “middle sphere”; magma:
hot
• Outer core: liquid layer molten metals
• Inner core: solid metal
Earth’s Layers
Continental Drift Theory
(Plate Tectonics)
Tectonic Plates
• Pieces of the Earth’s crust move on top of the
asthenosphere
• Each plate carries a continent, ocean basin or both
• Fit together like a jigsaw puzzle or cracked egg
• Drift apart to form rifts and valleys (sea-floor
spreading)
• Collide to form mountain ranges
• Some cracks called faults slip under great pressure
and cause release of energy as seismic waves
(earthquakes)
Pangaea
• Supercontinent of volcanic land masses
• Split apart into pieces and moved to form
the continents today as we know them
• Evidence includes same rocks found on
South American and African coasts and
fossils found on neighboring land masses