Earth

1
Table of Contents

• Earths Interior
• Convection and the Mantle
• Drifting Continents
• Sea-Floor Spreading
• The Theory of Plate Tectonics

2
Exploring Inside the Earth
- Earths Interior

• Earths surface is constantly changing. It looks
  very different today than it did millions of
  years ago.
• Geologists (scientists who study rocks) would
  have to dig down 6,000 kilometers to get to the
  Earths core.
• Because this would be impossible, geologists use
  two main types of evidence to learn about Earths
  interior

3
Exploring Inside the Earth
- Earths Interior

• Direct evidence from rock samples
• Indirect evidence from seismic waves.

4
Exploring Inside the Earth
- Earths Interior

• Seismic waves vibrations that travel through
  Earth carrying the energy released during an
  earthquake.
• Can detect the structure of the planet by
  studying the speed and path of the waves
• Determined that the Earth is made up of many
  layers

5
A Journey to the Center of Earth
- Earths Interior

• The three main layers of Earth
• crust, the mantle, and the core.
• Layers vary greatly in size, composition,
  temperature, and pressure.
• Temperature the heat is a result of the
  formation of the planet and radio active
  materials.
• Increases by about 1C every 40 meters down

6
A Journey to the Center of Earth
- Earths Interior

• Pressure force exerted on a surface divided by
  the area over which the force is exerted.
• Increases as you go deeper into the Earth

Pressure increases the deeper you go, like that
of a swimming pool
7
The Crust
- Earths Interior

• Crust layer of rock that forms Earths outer
  skin
• Includes both dry land and the ocean floor.
• Thinnest at ocean floors and thickest at
  mountains

8
The Crust
- Earths Interior

• Two types of crust
• Oceanic crust the crust that makes up the ocean
  floor
• Made mostly of basalts dark rock with a fine
  grained texture
• Continental crust the crust that makes up the
  continents
• Made mostly of granites light rock with a
  coarse grained texture

9
The Mantle
- Earths Interior

• Mantle layer of hot semi-solid rock under the
  crust
• Divided into layers based on the physical
  characteristics
• Total about 3,000 km thick

10
The Mantle
- Earths Interior

• Two parts to the upper mantle
• Lithosphere where the upper most part of the
  mantel and the crust merge
• lithos Greek for stone
• About 100 km thick
• Asthenosphere under the lithosphere where rock
  is heated causing it to be flexible (like
  plastic)
• asthenes Greek for weak
• Still considered a solid

11
The Core
- Earths Interior

• Lower mantle beneath the asthenosphere, very
  hot solid material
• Core in the center of Earth and made mostly of
  iron and nickel
• Consists of two parts outer and inner
• Total 3,486 km thick
• Outer core molten liquid metal
• Scientists think that movements in the liquid
  outer core create Earths magnetic field.
• Inner core dense ball of iron and nickel atoms
• So much pressure that it remains a solid

12
The Core
- Earths Interior

• The core is made mostly of the metals iron and
  nickel. It consists of two partsa liquid outer
  core and a solid inner core.

13
Temperature Inside the Earth
- Earths Interior

• The graph shows how temperatures change between
  Earths surface and the bottom of the mantle. On
  this graph the temperature at the Earths surface
  is 0oC. Study the graph carefully and then answer
  the questions.

14
Temperature Inside the Earth
- Earths Interior

• Reading Graphs
• As you move from left to right on the x-axis,
  how does depth inside the Earth change?

• The depth increases.

15
Temperature Inside the Earth
- Earths Interior

• Estimating
• What is the temperature at the boundary between
  the lithosphere and the asthenosphere?

• About 1,600oC

16
Temperature Inside the Earth
- Earths Interior

• Estimating
• What is the temperature at the boundary
  between the lower mantle and the core?

• About 3,200oC

17
Temperature Inside the Earth
- Earths Interior

• Interpreting Data
• How does temperature change with depth in
  Earths interior?

• It generally increases with depth.

18
Links on the Structure of Earth
- Earths Interior

• Click the SciLinks button for links on the
  structure of Earth.

19
Types of Heat Transfer
- Convection and the Mantle

• Heat always moves from a warmer substance to a
  cooler substance.
• Ex holding an ice cube in your hand
• There are three types of heat transfer
  radiation, conduction, and convection.

20
Radiation
- Convection and the Mantle

• Radiation the transfer of energy through space
• takes place with no direct contact between a heat
  source and an object
• Ex Sunlight

21
Conduction
- Convection and the Mantle

• Conduction the transfer of heat within a
  material or between materials that are touching
• Ex spoon in a pot of hot soup

In conduction, the heated particles of a
substance transfer heat through contact with
other particles in the substance.
22
Convection
- Convection and the Mantle

• Convection is caused by differences of
  temperature and density within a fluid.
• Density measure of how much mass there is in a
  volume of a substance.
• Ex A rock is more dense than the same volume of
  water.
• As a substance is heated, molecules spread apart,
  causing it to be less dense, and allowing it to
  rise
• As it cools the molecules get closer together,
  increasing density, and causing gravity to pull
  it back down.

23
Convection Currents
- Convection and the Mantle

• Heating and cooling of the fluid, changes in the
  fluids density, and the force of gravity combine
  to set convection currents in motion.

24
Convection Currents
- Convection and the Mantle

• Convection current movement of a fluid, caused
  by differences in temperature, that transfers
  heat from one part of the fluid to another.
• Continue as long as heat is added
• Without heat, convection currents eventually
  stop.

25
Convection Currents in Earth
- Convection and the Mantle

• Heat from the core and the mantle itself causes
  convection currents in the mantle.

26
Mantle Convection
- Convection and the Mantle

• Click the Video button to watch a movieabout
  mantle convections.

27
More on Convection Currents in the Mantle
- Convection and the Mantle

• Click the PHSchool.com button for an activity
  about convection currents in the mantle.

28
Continental Drift
- Drifting Continents

• Throughout centuries people have been studying
  maps. During this time many people have noticed
  the similarities between the coastlines of the
  continents.
• The continents on each side of the Atlantic Ocean
  looked as though they could fit together like a
  puzzle piece.

29
Continental Drift
- Drifting Continents

• Alfred Wegener (1910) German scientist who
  hypothesized that all of the continents were once
  joined together in a giant continent that he
  named Pangaea.
• Continental drift theory - idea that the
  continents slowly move across Earths surface
• Pangaea was believed to exist about 300 million
  years ago when reptiles and winged insects first
  appeared

30
Continental Drift
- Drifting Continents

• Wegeners hypothesis was that all the continents
  were once joined together in a single landmass.

31
Continental Drift
- Drifting Continents

• Wegener gathered three types of evidence to
  support his ideas about continental drift.
• They included land features, fossils, and
  evidence of climate change
• Evidence from land features
• Wegener found that the mountains of eastern South
  America matched that of western Africa
• Coal in England matched that of eastern North
  America

32
Continental Drift
- Drifting Continents

• Evidence From Fossils
• Wegener also used fossils to support his idea.
• Fossil any trace of an ancient organism that
  has been preserved in rock.
• Ex Glossopteris (250 mill yr old fern) found
  in rocks of Africa and South America

33
Continental Drift
- Drifting Continents

• Ex Mesosaurus and Lystrosaurus (ancient
  freshwater reptiles) now separated by an ocean
• Evidence From Climate
• Wegener found fossil evidence of ancient tropical
  plants and animals in polar regions
• He also found evidence of ancient arctic species
  in areas that are now close to the equator.

34
Evidence for Continental Drift
35
Evidence for Continental Drift
- Drifting Continents
36
Wegeners Hypothesis Rejected
- Drifting Continents

• Many scientists opposed Wageners hypothesis,
  despite the evidence, because he was unable to
  explain what the force was that caused this
  movement.

37
Links on Continental Drift
- Drifting Continents

• Click the SciLinks button for links on
  continental drift.

38
Mid-Ocean Ridges
- Sea-Floor Spreading

• The East Pacific Rise is just one of the many
  mid-ocean ridges that wind beneath Earths oceans.

39
Mid-Ocean Ridges
- Sea-Floor Spreading

• Mid-ocean ridge undersea mountain chain where
  new ocean floor is produced
• Discovered by using sonar (a device that bounces
  sound waves off underwater objects and then
  records the echoes)

• Harry Hess (American) first geologists to study
  mid-ocean ridges
• Found evidence to back up Wegeners Continental
  Drift Theory
• Called this seafloor spreading

40
What Is Sea-Floor Spreading?
- Sea-Floor Spreading

• Sea-floor spreading sea floor spreads apart
  along both sides of a mid-ocean ridge as new
  crust is added
• Ocean floors move like conveyor belts, carrying
  the continents along with them.

41
Evidence for Sea-Floor Spreading
- Sea-Floor Spreading

• Hess found evidence to support his theory of
  sea-floor spreading, which included
• eruptions of molten material, magnetic stripes in
  the rock of the ocean floor, and the ages of the
  rocks themselves.

42
Evidence for Sea-Floor Spreading
- Sea-Floor Spreading

• Evidence From Molten Material
• 1960s submarine Alvin found rocks along the
  ocean floor running parallel with the ridge
• These type of rocks only form when molten
  material hardens quickly after erupting under
  water
• Evidence From Magnetic Stripes
• rock that makes up the ocean floor lies in a
  pattern of magnetized stripes.
• record of reversals in Earths magnetic field.

43
Evidence for Sea-Floor Spreading

• Evidence From Drilling Samples
• Glomar Challenger (1968) drilling ship that
  obtained rock samples from the ocean crust
• Found that the rocks closest to the mid-ocean
  ridge were younger.
• The farther away from a ridge the samples were
  taken, the older the rocks were

44
Subduction at Trenches

• Deep-ocean trench deep valley along the ocean
  floor beneath which oceanic crust slowly sinks
  toward the mantle.
• The oceanic crust bends downward into the mantle
• Subduction process by which oceanic crust sinks
  beneath a deep-ocean trench and back into the
  mantle.
• Occurs at a convergent plate boundary

Trench
Subduction
45
Subduction at Trenches
- Sea-Floor Spreading

• In a process taking tens of millions of years,
  part of the ocean floor sinks back into the
  mantle through deep-ocean trenches.

46
Growing an Ocean
- Sea-Floor Spreading

• Because of sea-floor spreading, the distance
  between Europe and North America is increasing by
  a few centimeters per year.

47
More on Sea-Floor Spreading
- Sea-Floor Spreading

• Click the PHSchool.com button for an activity
  aboutsea-floor spreading.

48
Sea-Floor Spreading
- Sea-Floor Spreading

• Click the Video button to watch a movieabout
  sea-floor spreading.

49
How Plates Move

• Plate tectonics theory that pieces of Earths
  lithosphere are in constant motion, driven by
  convection currents in the mantle.
• As the plates move, they collide, pull apart, or
  grind past each other, producing spectacular
  changes in Earths surface.
• Changes include volcanoes, mountain ranges, and
  deep-ocean trenches.

50
How Plates Move
- The Theory of Plate Tectonics

• The theory of plate tectonics explains the
  formation, movement, and subduction of Earths
  plates.

51
Plate Boundaries

• The edges of Earths plates meet at plate
  boundaries that extend deep into the lithosphere.
• Fault break in Earths crust where masses of
  rock slip past each other.

52
Plate Boundaries
- The Theory of Plate Tectonics

• There are three kinds of plate boundaries
• divergent boundaries, convergent boundaries, and
  transform boundaries.
• A different type of plate movement occurs along
  each type of boundary.

53
Calculating a Rate
- The Theory of Plate Tectonics

• To calculate the rate of plate motion, divide the
  distance the plate moves by the time it takes to
  move that distance.
• Rate distance/time
• For example, a plate takes two million years to
  move 156 km. Calculate its rate of motion.
• 156 km/2,000,000 years 7.8 cm per year

54
Calculating a Rate
- The Theory of Plate Tectonics

• Practice Problem
• The Pacific plate is sliding past the North
  American plate. It has take ten million years for
  the plate to move 600 km. What is the Pacific
  plates rate of motion?
• 60,000,000cm 10,000,000years 6 cm/yr

55
Plate Boundaries
- The Theory of Plate Tectonics

• Divergent boundary plate boundary where two
  plates move away from each other.
• Most divergent boundaries occur along the
  mid-ocean ridges where sea-floor spreading
  occurs.
• Rift valley deep valley that forms where two
  plates move apart.
• Ex Great Rift Valley in Africa

56
Plate Boundaries
- The Theory of Plate Tectonics

• Convergent boundary plate boundary where two
  plates move toward each other.
• The density of the plates determines which one
  comes out on top.

• Ex Oceanic Continental collision
• Oceanic crust is more dense, therefore subduction
  occurs
• Ex Continental Continental collision
• Neither is more dense, therefore mountains form

Ex Appalachia Mountains
57
Plate Boundaries
- The Theory of Plate Tectonics

• Transform boundary plate boundary where two
  plates move past each other in opposite
  directions.
• Earthquakes often occur along transform
  boundaries, but crust is neither created nor
  destroyed.

Ex San Andreas Fault, California
58
Continental Drift
- The Theory of Plate Tectonics

• It has taken the continents about 225 million
  years since the breakup of Pangaea to move to
  their present locations.

59
Continental Drift Activity
- The Theory of Plate Tectonics

• Click the Active Art button to open a browser
  window and access Active Art about continental
  drift.

60
Graphic Organizer
Type of Boundary
Type of Motion
Effect on Crust
Feature(s) Formed
Plates slide past each other.
Crust is sheared.
Strike-slip fault
Transform boundary
Plates move together.
Subduction or mountain
Convergent boundary
Mountains, volcanoes
Mid-ocean ridge, ocean floor
Plates move apart.
Divergent boundary
Crust pulled apart