The Earth as a Planet

1
The Earth as a Planet

• Understanding the Earth

2
Earths Position in the Solar System

• The Earth is the third planet from the Sun with
  an average distance from our star of about 93
  million miles. It is uniquely distanced from the
  Sun so that the majority of the water on our
  surface remains in its liquid state.

3
Earths Shape and Size

• Even ancient astronomers knew that the Earth was
  spherical and had a radius of about 6400
  kilometers (4000 miles).

4
Why is the Earth Round

• Ancients believed that God made the World
  perfectly, therefore the Earth was created in the
  shape of a circle. Today we look for a more
  scientific view to explain the Earths shape.

5
Why is the Earth Round

• Gravity is the great leveler of the Universe.
  Its constant force pulls on the Earth
  ceaselessly. This constant pull toward the
  center of the planet deforms rock into a sphere.

6
Why is Everything Not Round Then?

• A certain radius and density are required for an
  object to have enough mass to become spherical.
  That radius is about 350 kms. Smaller objects
• retain their irregular
• shapes because they
• lack the gravitational
• forces needed to make
• themselves round.

7
The Earth Really Isnt Round!

• Despite the fact that it may look like it, the
  Earth isnt round at all. The equatorial
  distance is approximately 21 kms (13 miles)
  longer than the Earths circumference measured
  around the poles. This doesnt come as any
  great surprise.
• Newton and Hooke
• both speculated
• that this was true.

8
The Earth Really Isnt Round!

• The Earths bulge is caused (in part) by the
  increased rotational speed of the planet as you
  near the poles.
• A point near the poles spins
• much more slowly than one
• near the equator. With
• increased speed comes
• increased centrifugal force.

9
The Earths Bulge

• It is this additional centrifugal force that
  forces the equatorial regions of the Earth
  outward. A good example is a CD on your
  dashboard when you go around a corner. The turn
  creates a force perpendicular to the direction of
  the curve that slides your CD away from you.

10
The Bulge And global warming

• Scientists have recently linked changes in the
  Earths expanding equator, dubbed equatorial
  obesity, to climatic changes caused by global
  warming.

11
The Bulge And global warming

• As the ice caps melt, water is freed to move.
  Because of centrifugal force, this water
  accumulates at the Earths equator, exaggerating
  the planets bulge.

12
The Earths Bulge

• This bulging equatorial region could actually
  effect the period of the Earths rotation. The
  fatter the bulge, the slower the planet will
  spin. Scientists have already seen evidence of
  this following the tsunami of December 24, 2004.

13
Composition of the Earths crust

• Element Percent of Density (g/cm3)
• element by
• mass
• Oxygen 45
• Silicon 27 2.42
• Aluminum 8 2.70
• Iron 6 7.90
• Calcium 4.6 1.55
• Magnesium 2.7 1.74
• Sodium 2.3 0.97
• Potassium 1.8 0.87
• Titanium 0.6 4.50

14
Density of the Earth

• Density is the measure of how much material is
  in a given area. Mathematically, it is
  mass/volume. The Earths average density is
  about 5.5g/cm3. This is about 2 times greater
  than ordinary rock. So, the rest of the material
  that the Earth is made of must be considerably
  denser.

15
Density of the Earth

• What must the remainder of the Earth be made of
  to account for this high average density? The
  answer is iron!

16
The Earths Interior

• What we know about the Earths interior comes
  mainly from seismic information. Earthquakes
  generate two distinctive waves.
• The first type of wave is the P-wave. It is a
  compression wave. The other type is the
  S-wave. It travels perpendicular to the
  direction of its propagation.

17
Seismic Waves

• P-waves have the ability to travel through both
  solid and liquid mediums. S-waves can only
  travel through solids. The Earths liquid core
  creates a seismic shadow for S-waves between
  earthquake monitoring stations and earthquake
  epicenters. In that wave, the Earths liquid
  regions may be mapped.

18
The Earths Interior

• Heat flows outward from Earth's interior. The
  crust insulates us from Earth's interior heat.
  The mantle is semi-molten, the outer core is
  liquid and the inner core is solid.

19
The Earths Interior Heat

• Where does the heat originate that drives
  Earths geologic engine? It comes from natural
  radiation! It is estimated that the Earths
  temperature rises about 2 Kelvin/100 meters. The
  center of the Earth is estimated to be
  approximately 6500 Kelvin, hotter than the
  surface of the Sun.
• Also, the Earth was
• born in heat due to
• collisions with other
• bodies as it accreted.

20
The Earths Interior Heat

• It is estimated that the Earths temperature
  rises about 2 Kelvin/100 meters. The center of
  the Earth is estimated to be approximately 6,500
  Kelvin, hotter than the surface of the Sun.

21
Building A Planet

• In addition to the
• heat from
• radiation, the
• Earth also once
• got a lot of its
• heat from
• accretion.

22
Building A Planet

• Accretion is the process where bodies in space
  collide and stick together. This is how planets
  grow bigger and bigger over time. The process of
  accretion releases tremendous amounts of heat
  that
• the Earth stores.

23
The Earths Interior

• What we know about the Earths interior comes
  mainly from seismic information. The word
  seismic means earthquake. Earthquakes generate
  two distinctive seismic (earthquake) waves.

24
Seismic Waves

• The first type of wave is the primary or
  P-wave. It is a compression wave. It travels
  parallel to the direction of propagation. The
  other type is the secondary or S-wave. It
  travels perpendicular to the direction of its
  propagation. Propagation is how waves move.

25
Seismic Waves

• Earthquakes generate P-waves that propagate
  through both solids and liquids and S-waves that
  travel only through solids. Both waves also
  travel at different speeds. Using this
  information, seismologist or earthquake
  scientists, can tell where earthquakes start.
• P-waves and S-waves are generated by earthquakes.

26
Seismic Wave Terms

• The point where an earthquake begins, deep in
  the Earths crust is called the focus.
• The point on the Earths surface directly above
  the focus is called the epicenter.
• The plane along which the land moves is called
  the fault.

27
Seismic Waves

• The Earths liquid core creates a seismic
  shadow for S-waves between earthquake monitoring
  stations and earthquake epicenters. In that
  wave, the interior liquid regions of the Earths
  may be mapped.

28
The Earths Exterior

• The Earths crust is made of lithospheric
  plates. There are 12 major plates and a handful
  of minor ones. These plates consist of the
  Earths crust and upper mantle. These combined
  layers are known as the asthenosphere.
• Water in the upper
• mantle provides a
• slick surface along
• which the plates ride.

29
Tectonic Plates

30
Plate Tectonics

• Now that we know we ride of plates, what makes
  them move? It is believed to be convection cells
  within the Earths interior.
• Convection
• cell

31
Plate Tectonics and convection cells

• Convection cells are caused by temperature
  differences within a body of liquid. Hotter
  portions of the liquid have less density and rise
  while cooler portions of the liquid have greater
  density and fall.

32
So, what Causes Earthquakes?

• Tectonic plates are sort of like rafts floating
  in a swimming pool. The circulating water in the
  pool makes them float around. Tectonic plates
  are similar as they float around on top of the
  Earths molten mantle (the asthenosphere).

33
So, what Causes Earthquakes?

• Occasionally, the edges of plates get caught or
  stuck together. When this happens, stress builds
  up. Eventually enough stress builds to make the
  plates slip past each other. This sudden release
  is called an earthquake.

34
Alfred Wegener and Continental Drift
35
Alfred Wegener

• German Alfred Wegener was born in 1880 and
  attended the University of Berlin in his teens.
  Later, while tutoring at the University of
  Marburg he found an article that compared similar
  fossils found on both sides of the Atlantic
  Ocean. He began to try to make sense of this and
  understand why.

36
Fossil Evidence
37
Puzzle Evidence

• He also noticed that the coastlines of the
  continents on both sides of the Atlantic Ocean
  matched each other like a giant jigsaw puzzle.

38
Landform and Structural Evidence

• In addition, he saw that mountain ranges and
  landforms in North and South America had
  counterparts in Europe and Africa. An example is
  the Scottish Highlands and the Appalachian
  Mountains here in N.C.

39
Landform and Structural Evidence

• Another example is the Karroo Mountain system of
  South Africa which is identical to the Santa
  Catarina Mountain system in Brazil.

40
Evidence of Continental Drift

• From this evidence, Wegener concluded that long
  ago all the Earths land had been joined into one
  giant landmass and had drifted apart. He called
  this original landmass Pangaea.

41
From Continental Drift to Plate Tectonics

• It was not until the early 1960s when the
  mechanism for continental drift was discovered
  and understood that todays modern theory of
  plate tectonics was created.
• Tectonic plate map

42
From Continental Drift to Plate Tectonics

• Seafloor mapping during the Cold War (for
  submarines) discovered deep volcanic mountains
  that wrapped the entire Earth like the seams on a
  baseball.
• Seafloor Map Aleutians

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Plate Tectonics Creation AND DISTRUCTION OF land

• New land is constantly being created and
  destroyed in the Earths crust. If only new
  crust was being created the Earth would get
  bigger and bigger like an inflating balloon.
  Fortunately, old land is destroyed at the same
  rate that new land is created and the Earth
  remains a constant size.

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Plate Tectonics Creation AND DISTRUCTION OF land
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The Theory of Plate Tectonics

• The complete theory of plate tectonics states
  that
• The Earths crust and upper mantle, which are
  made up of large plates, move
• These plates are driven by convection cells that
  originate deep within the Earth
• There are areas where new crust is being created
  and
• There are areas where old crust is being
  destroyed.
• Weve seen the plates, so where is the new land?

48
Plate Tectonics Creation

• Areas where new crust is being made are called
  induction zones. They happen at divergent
  boundaries where plates are created and spread
  apart. Like toothpaste from a tube, hot magma is
  squeezed from undersea mountain ranges called
  seamounts.
• Juan De Fuca Ridge

49
Plate Boundaries Divergent Boundaries

• Divergent boundaries are very hard to see
  because they are located in the deepest parts of
  the worlds oceans. Because of where it happens,
  this process is referred to as seafloor
  spreading.
• Undersea black smoker
• in a seamount

50
Divergent Boundaries A.K.A seafloor spreading
51
Divergent Boundaries and magnetic orientation

• The magnetic components in molten lava orient
  themselves along the Earths magnetic field.
  When this magma squirts out and crystallizes, it
  freezes this magnetic orientation into the
  solid rock.

52
Divergent Boundaries and magnetic orientation

• Scientists detect these magnetic stripes with
  an instrument called a magnetometer. From this
  information they can learn rates of seafloor
  spreading and the changes in the Earths magnetic
  field over time.

53
Plate Tectonics destruction

• Old land is destroyed at convergent boundaries.
  Older rock is more dense and heavier. This land
  slides beneath the edges of other plates and the
  land converges. As it goes deeper into the
  Earths interior, this land eventually melts to
  be recycled into new land. The areas are called
  subduction zones.

54
Plate Boundaries Convergent Boundaries

• Areas where plate boundaries converge are easy
  to identify. They are regions of heavy volcanic
  activity. The margin of the Pacific Ocean is
  called the Pacific Ring of Fire for the
  abundance of volcanoes that surround it. This is
  where the Pacific plate slides under several
  others.

55
Identifying Subduction Areas

• Subduction zones can be identified by two
  structures that accompany them. These are
  continental volcanic arcs and volcanic island
  arcs.

56
Continental Volcanic Arcs

• Continental volcanic arcs form where subduction
  occurs under land.

57
Volcanic Island Arcs

• Volcanic island arcs are seen where subduction
  occurs under the sea.

58
Plate Boundaries Transform Fault Boundaries

• In addition to convergent an divergent plate
  boundaries, there is another type called the
  transform fault boundary. The most famous of
  these is the San Andreas fault in California.

59
Transform Faults

• Transform faults are areas where plates slide
  past one another, not over or under. The San
  Andreas Fault is formed by the North American
  Plate sliding past the Pacific Plate. Transform
  faults are neither constructive nor destructive.

60
Volcanoes and Volcanism

• Now that you know about subduction zones and
  their relationships with volcanoes, you might
  think that volcanoes only occur in these areas.
  That is not true. Volcanoes also occur over hot
  spots, like the Hawaiian Islands.

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Hot Spot Volcanoes

• A hot spot is a place where hot magma from the
  Earths mantle pushes through the Earths crust.
  Hot spots are pretty stable in that the last a
  long time and move very little.

62
Hot Spot Volcanoes

• One of the best examples of this is the Hawaiian
  Islands. As the Earths crust moves over the hot
  spot, like blusters, volcanoes form. This trail
  of blisters is what we call Hawaii.

Direction of Travel
63
Hot Spot Locations

• This is a map of hot spot locations. There are
  11 located in Antarctica that are not shown.

64
Hot Spot
65
Summary

• Earths density is high because its made of
  iron primarily. It is made of a solid inner
  core, a liquid outer core, a plastic mantle and a
  rigid crust. Heat from inside the Earth rises
  from the core when hot and falls toward the core
  as it cools, creating convection cells. These
  cells move the Earths crust around which
  consists of 12 major plates called lithographic
  plates.

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Summary

• Plates do certain things when they meet at their
  boundaries. They ride over, under or past
  adjacent plates. These boundaries are called
  constructive, destructive and transform
  boundaries. Constructive boundaries are
  induction zones where magma is squeezed out of
  deep ocean seamounts producing new land.
  Destructive boundaries are subduction zones where
  one plate slides under another and melts into
  magma to be recycled. Transform boundaries are
  where plates slide past each other. They are
  neither constructive or destructive.

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Summary

• Sometimes as plates slide relative to one
  another, they stick together and stress builds
  between them. Stress builds until the plates
  violently shift causing an earthquake. The point
  beneath the crust where the earthquake starts is
  called the focus. The point above the focus at
  the Earths surface is called the epicenter. The
  plane along which the movement between the plates
  occurs is called the fault.
• Earthquakes generate two kinds of waves primary
  or P-waves and secondary/surface waves or
  S-waves. P-waves pass through solids and
  liquids, while S-waves travel only through
  solids. Scientists use these facts to determine
  the epicenters of earthquakes. P-waves move
  about 8 km/hours and S-waves travel about 5
  km/hr. P-waves travel straight and S-waves
  perpendicular to their direction of propagation.

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Summary

• Constructive boundaries are located deep in the
  oceans and are seamounts where molten rock is
  forced from them. Extremely long seamounts,
  thousands of miles long, crisscross the ocean
  floor.
• Destructive boundaries are located at the edges
  of plates where one plate is subducted or passes
  under another plate. These are areas of intense
  seismic activity with many volcanoes and frequent
  earthquakes.

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Summary

• Subduction areas (destructive margins) are
  easily recognizable. In addition to seismic
  activity, they are also areas of mountain
  building or orogeny. Some orogenic events are
  still going on. An example is the Indian Plate
  subducting beneath the Eurasian Plate. This is
  the process that continues to build the Himalayan
  Mountains. Mountains tell you where plate
  boundaries exist, past and present.

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Summary

• Alfred Wegener suggested the theory of
  continental drift because of fossil and geologic
  evidence (similar species, puzzle pieces and
  similar landforms) he had observed. He proposed
  that once, one giant continent existed he called
  Pangaea. From this supercontinent all our
  present land drifted via plate tectonics. The
  difference in the theories of continental drift
  and plate tectonics is that continental drift
  does not account for why the continents move.
  Plate tectonics says plates move due to
  circulation cells beneath the Earths crust.

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Summary

• Magnetism Other, modern evidence of plate
  tectonics does exist. Magnetic striping on the
  seafloor leaves tracks from the formation of new
  crust. From this information scientist can study
  paleomagnetism or the orientation and
  fluctuation of the Earths magnetic field. The
  instrument that reads these magnetic differences
  is called a magnetometer.

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The Age of the Earth

• The age of the Earth is relatively easy to
  determine using radioactive dating. Inside each
  rock is trapped some amount of radioactive
  material. Over time, this radioactive material
  decays into daughter atoms or products. This
  decay happens at a known rate called half-life.

73
The Age of the Earth

• Scientists estimate that the oldest rocks on the
  Earth are approximately 4 billion years old and
  that the age of the planet is somewhere around
  4.65 billion years old. Most of Earths oldest
  rock have been destroyed by geologic processes.

74
The Earths Exterior

• The Earths crust is made of lithospheric
  plates. There are 12 major plates and a handful
  of minor ones. These plates float consist of the
  Earths crust and upper mantle. These combined
  layers are known as the asthenosphere.
• Water in the upper
• mantle provides a
• slick surface along
• which the plates ride.