Composition of the Earth. The Size of the Earth The Earth is almost spherical with a radius of...
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Transcript of Composition of the Earth. The Size of the Earth The Earth is almost spherical with a radius of...
Composition of the Earth
The Size of the Earth The Earth is almost spherical with a
radius of nearly 6 400 km. Variations in the value of acceleration
due to gravity “g” at the surface prove that the Earth is not perfectly spherical.
The composition of the Earth varies with depth.
The layers are thought to have developed billions of years ago.
The Earth is Made of Layers
CrustMantleOuter Core
Inner Core
Earth has a layered structure
Atmosphere and Hydrosphere
Low Density Crust
Intermediate Density Mantle
High density core Liquid outer core Solid inner core
Not in your notes.
CrustThis is the outermost layer. We have not been able to penetrate it completely. It varies in thickness from as thin as 5 km under
the oceans to as thick as 60 km under the continents. (Averages less than 20 km thick.)
Continental crust is different from oceanic crust.
Oceanic crust is basalt-like. It is high in silicon and magnesium.
Continental crust is granite-like. It is high in silicon and aluminum.
Mantle Lies beneath the crust. Over 80% of the Earth’s volume. It is 2 900 km thick. Solid, rocky layer It is composed of ultramafic rock
(rock that is rich in iron and magnesium)
Mantle It is thought to have the same
chemical composition throughout but a varying mineral composition (pressure causes a structural change between the atoms resulting in different minerals)
Mantle
Lithosphere Includes the crust and upper
mantle Is approximately 100 km thick It is strong and brittle It makes up the “plates” in plate
tectonics
Asthenosphere Is a layer within the mantle that
extends approximately 150 km below the lithosphere.
It is thought to be the zone of magma production. At this depth rocks are closest to their melting point.
Asthenosphere It contains weaker rock that
deforms easily. It is thought to be a lubricating
layer for the plates. Movements within this layer are
thought to induce motion in the rigid lithosphere above
Outer Core Is 2 250 km thick liquid mostly iron and nickel
Inner Core 2 400 km in diameter Solid Mostly iron and nickel
The Earth’s Magnetic FieldThe Earth acts as if a large bar magnet was buried at its core.
The Earth’s Magnetic FieldSince the Earth’s core is too hot for any material to retain its magnetism (Currie point exceeded) motion must be occurring. This idea is also supported by the fact that the magnetic poles appear to be slowly moving around the geographic poles.
It is thought that the magnetic field is created by electric currents within the slowly circulating liquid part of the core.
Density Varies With Depth
Not in your notes.
Temperature Varies With Depth
Not in your notes.
Temperature Varies With Depth Within the upper crust, temperature
increases with depth at 25°C / km Temperature increases then tapers to
1°C / km This means that deeper mines must be
cooled for human survival. This also means that drilling equipment
becomes soft and flexible unless continuously cooled.
Source of Earth’s Heat Heat is thought to come from:
Left-over heat from the Earth’s formation
Friction (rotation; moving plates)Radioactive decay (which is most
important) Since rock is a good insulator, little
heat is lost.
Heat Flow from Oceans and Continents
The Protoplanet Hypothesis
About 5 billion years ago an existing, slowly rotating 10 billion km (diameter) cloud of gas and dust began to collapse.
Collapse caused it to spin faster and heat up.
Most of the mass was concentrated as the sun.
Smaller clusters of matter not captured by the sun began to collect.
These became protoplanets.
Collisions continued over time forming planets and moons.
Uncollected material still exists as asteroids and comets.
The protoplanet Earth evolved as it grew hotter from: Gravitational collapse Radioactive minerals Bombardment by meteor showers
As a result, iron melted and sank toward the centre.
Lighter materials rose. Earth became differentiated into
layers. Escaping steam from the
protoplanet formed our oceans.
Differentiation of the Earth
(a) Early homogenous Earth
(b) Lighter matter “floats” toward surface
(c) Modern structure of the Earth
Not in your notes.
Earth’s CompositionEarth’s Composition
Elements are not distributed evenly throughout the layers.
Not in your notes.
Not in your notes.
Earth’s LayersThickness
(km)Volume1027 cm3
Densityg/cc
Mass1027 kg
MassPercen
t
Atmosphere0.00000
50.0000
9
Hydrosphere 3.80 0.00137 1.03 0.00141 0.024
Crust 17 0.008 2.8 0.024 0.4
Mantle 2883 0.899 4.5 4.016 67.2
Core 3471 0.175 11.0 1.936 32.4
All 6371 1.083 5.52 5.976 100.00
Not in your notes.
Assignments Layers of the Earth assignment
sheet From Chapter One
Review p. 14 Critical Thinking p. 15
From Chapter Two Topic Questions 4, 6,7 Review p. 26 (1-18)