Earth

1
Earths Changing Crust
2
Vocabulary
fault Cracks in the crust
Geologists Scientists who study the Earth
Magma Hot molten rock deep below the Earths surface
Lava Magma that reaches the Earths surface
Weathering Breaking down rocks into smaller pieces
Erosion The picking up and carrying away of pieces of rock
Deposition The dropping off of bits of eroded rock
Meteorite Rocks from space that strike a surface
3
What Makes the Crust Move

• http//videos.howstuffworks.com/howstuffworks/236-
  how-earthquakes-work-video.htm

4
Forces on and Under Earth Shape Its Surface

• The Earths crust is constantly moving.
• Earthquakes are related to cracks in the crust
  called faults.
• San Andreas Fault

5

• During an earthquake the crust on either side, or
  both sides of a fault is in motion.
• Vibrations travel through the crust. The farther
  away people are from the earthquake, the harder
  it is to feel the vibrations.
• Seismographs record the motion at locations all
  around the crust.

6

• Most of the time the crust moves VERY slowly and
  people only notice when there is a visible
  change.
• To measure crust movement, surveyors measure
  elevation (how high a place is above sea level).
• Geologists place sensitive devices all along
  faults. They hope that records of tiny movements
  can be used to predict an earthquake.

7
Plate Tectonics

• The crust is the Earths hard surface.
• It is very thin.
• About one-thousandth of the Earths thickness

8
Plate Tectonics

• The Mantle
• Located under the crust
• Earths thickest layer
• Rock material here is solid, however it can flow
  like a liquid. (Like putty does when you squeeze
  it.)
• Rock material is always in motion like heated
  water in a pot.
• It rises and pushes against the bottom of the
  crust. This causes it to break into pieces, or
  plates.
• Earthquakes and slow motions of the crust result
  from moving plates.

9
Plate Tectonics

• Earths Core
• Located below the mantle
• Two parts
• A liquid Outer Core
• A solid Inner Core

10
What Forces Act On The Crust

• http//videos.howstuffworks.com/howstuffworks/236-
  how-earthquakes-work-video.htm

11
What Forces Act on the Crust?

• As plates of the crust move they can collide,
  pull away from each other, or slide past each
  other.
• These movements cause 3 kinds of force to act on
  the crust.
• 1. Tension stretches or pulls apart the crust
• 2. Compression squeezes or pushes together the
  crust
• 3. Shear twists, tears, or pushes one part of
  the crust past another

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• Forces in the crust cause a fault to form and
  movement is caused along the faults.
• Compression can crumple rock layers into wavy
  folds. When two pieces of crust crash together,
  mountains are formed.
• Mountains made of folded and crumpled layers are
  called fold mountains (Appalachians, Alps, and
  Himalayas)

13
Volcanoes

• Tension and shear can also build up the crust.
  Mountains can be formed as the crust is pulled
  apart.
• Hot molten rock deep below the Earths surface
  (magma) rises upward. If this reaches the
  surface it may flow out as lava.
• Lava flows out when a volcano erupts.
• Volcanoes can also form islands.

14
Check This Out!

• Hawaii Big Island Volcano eruption

15
Fault-block Mountains

• Tension and shear can cause great blocks of crust
  to break apart cleanly and move along faults.
  This forms fault-block mountains.

16
What Other Forces Shape the Earths Surface?

• While movements of the crust are building up the
  Earths surface, other forces are breaking it
  down.
• Weathering
• Erosion

17
Weathering

• The breaking down of the materials of Earths
  crust into smaller pieces.
• Occurs when the crust is exposed to water, air,
  and changes in temperature.
• http//www.uky.edu/AS/Geology/howell/goodies/elear
  ning/module07swf.swf

18
How Does Weathering Occur?

• Water can dissolve some minerals right out of the
  crust.
• Moving water can make pieces of rock bang into
  each other.
• Small chips break off of the surface of the rock
  causing the rock to get smaller and rounder.
• Churning waters of a stream can wear down big
  pieces of rock into small, rounded pebbles.

19
How Does Weathering Occur?

• The wind blows sand and other bits of broken bits
  of rock over Earths surface. These particles
  also wear away rock.
• When temperatures are low enough, water freezes
  and expands. The force of expanding water is so
  great that it can split rock apart.
• Changes in temperature can also cause rock to
  expand and contract. When parts of a rock expand
  or contract more than others it can cause the
  rock to break apart.

20
Chemical Weathering

• Air contains gases that react chemically to form
  new substances.
• Oxygen in air reacts with iron to form rust.
• Carbon dioxide and sulfur dioxide in air react
  with rain to form acids.
• These acids eat away at limestone rock.

21
Erosion

• The carrying away of pieces of weathered rock by
  gravity, water, wind, and ice.
• Erosion can carry away a boulder, hill, or even a
  mountain range piece by piece.
• Water is the greatest agent. Each drop of water
  falling from the sky erodes the land.
• Water moving downhill picks up pieces of rock and
  carries them downhill. The faster the water the
  bigger the pieces of rock.

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What Does This All Look Like?

• HowStuffWorks Videos "Basics of Geology Erosion
  and Weathering"

23
How Can Wind Erode Rock?

• Wind does not exert as hard a push as water
  moving.
• Wind mostly erodes pieces of rock that are the
  size of sand particles or smaller.

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How Can Ice Erode Rock?

• Ice causes lots of erosion.
• When ice of a glacier freezes onto rock and then
  the glacier moves downhill, the rock is torn
  right out of the ground. It can carry chunks of
  ice bigger than your house with ease.
• Glaciers also wear away the land. Rocks of all
  sizes become frozen to the bottom of the glacier.
  As the glacier moves the rock beneath it is
  scratched and worn down.

25
Ice and Sand Experiment

• Describe in detail what you observed during the
  experiment.

26
Where Do Eroded Rocks Go?

• They are dropped to the bottom of the stream,
  lake, or ocean when the water stops moving.
  (DEPOSITION)
• Deposition takes place when glaciers melt and
  wind stops blowing.
• Layer by layer, pile after pile, bits and pieces
  of rock deposited by the water, wind, and ice
  build up on Earths surface.
• Deposition eventually fills up depressions in the
  Earths surface. It can build up land along shore
  lines.

27
What Forces Shape The Moons Surface?

• Without air and water, there can be very little
  weathering or erosion.
• The only weathering and erosion is due to the
  impact of rocks from space hitting the Moons
  surface (meteorites).
• Some craters formed by meteorites are big enough
  to be seem from Earth.
• Earths atmosphere protects its surface from such
  impacts. Rocks from space burn up as they pass
  through our atmosphere.