Earth

1
Earths Structure
2
Origin of the Earth

• Meteors and Asteroids bombarded the Earth

Earth is 4.6 billion years old
3
Earths Interior

• Core

• dense

• Iron and Nickel

• Inner Core - solid

• Outer Core - liquid

• Mantle

• Less dense than core

• Iron and Magnesium silicates

• Mostly solid

• Upper mantle is partially molten

• Crust

• Outermost layer

• Very thin and rigid

• Continental granite
• Density 2.8 g/cm3

• Oceanic basalt
• Density 3.0 g/cm3

4
Evidence of Internal Structure

• Density
• calculate density of Earth
• Speculate on probable compositions

• Meteorites
• Use composition and age to determine composition
  and age of Earth

• Seismic waves
• Travel times and direction give indication of
  internal structure of Earth

5
Earths Structure
6
Earths Layers
7
Types of Seismic Waves

• P waves

• Primary waves

• Push and pull movement

• Travel fastest ( 6 km/sec)

• Travel thru solids and liquids

• S waves

• Secondary waves

• Move side-to-side

• Slower ( 4 km/sec)

• Travel thru solids only

8
Seismic Waves Through Earth
9
Continents Today
10
Continental Drift Theory

• In 1912 a German meteorologist and explorer named
  Alfred Wegener presented a theory that the
  continents were once joined together in one land
  mass and have over millions of years slowly
  drifted apart into their present positions as we
  see them today. He named the supercontinent
  Pangaea after the Greek word meaning all land.

11
Continental Drift Geographic Fit

• Continents seem to fit together like pieces of a
  puzzle

12
Continental Drift Theory

• Through Wegeners research he found evidence to
  support his theory
• Fossils of Glossopteris, a seed fern, was found
  in India, Australia, South America, Africa and
  Antarctica
• Fossils of Mesosaurus, a small reptile were found
  in freshwater deposits in Africa South America.

13
Continental DriftFossils

• Similar distribution of fossils such as the
  Mesosaurus

14
Glossopteris

• Fern

15
Continental Drift

• Layers of the mountains found in S.E. Brazil,
  South America and S.W. Africa line up layer for
  layer in exact format.
• Continents look like puzzle pieces that could fit
  together.

16
Continental DriftMountains

• Mountain ranges match across oceans

17
Continental DriftGlaciation

• Glacial ages and climate evidence

18
Continental Drift ModelProblems

• Alfred Wegener

• Presented research to professionals

• Did not provide a plausible mechanism to explain
  how continents drifted

19
Seafloor Spreading

• Continental drift reexamined in 1960s with new
  information

• New theory developed Seafloor spreading

• Supporting evidence for seafloor spreading

• World seismicity

• Volcanism

• Age of seafloor

• Paleomagnetism

• Heat flow

• Theory combining continental drift and seafloor
  spreading termed Plate Tectonics

20
Seafloor Spreading

• New sea floor created at the mid-ocean ridge and
  destroyed in deep ocean trenches

21
Evidence for Seafloor SpreadingWorld Seismicity

• Earthquake distribution matches plate boundaries

22
Evidence for Seafloor SpreadingVolcanism

• Volcanoes match some plate boundaries some are
  hot spots

23
Evidence for Seafloor SpreadingAge of Seafloor

• Youngest sea floor is at mid-ocean ridge
• Oldest sea floor away from mid-ocean ridge

24
Evidence for Seafloor SpreadingPaleomagnetism

• Earth has a magnetic field - Probably caused by
  rotation of solid inner core in liquid outer core
  (both mostly Fe)

• When rocks cool at the Earths surface, they
  record Earths magnetic field (normal or reverse
  polarity)

25
Evidence for Seafloor SpreadingPaleomagnetism

• Paleomagnetic studies indicate alternating
  stripes of normal and reverse polarity at the
  mid-ocean ridge.

26
Seafloor SpreadingConvection Currents

• In 1960, proposed as driving force to move
  continents

27
Theory of Plate Tectonics

• John Tuzo Wilson combined ideas of continental
  drift and seafloor spreading into Plate
  Tectonics

28
Principles of Plate Tectonics

• Earths outermost layer composed of thin rigid
  plates moving horizontally

• Plates interact with each other along their edges
  (plate boundaries)

• Plate boundaries have high degree of tectonic
  activity
• mountain building
• earthquakes
• volcanoes

29
Plate BoundariesThree types

• Divergent

• Convergent

• Transform

30
Plate BoundariesDivergent

• Plates move away from each other

• New crust is being formed

31
Divergent Plate BoundariesExamples
East African Rift
Mid-Atlantic Ocean Ridge
32
Plate BoundariesConvergent
Three Types

• Ocean-continent

• Ocean-ocean

• Continent-continent

• Plates are moving toward each other

• Crust is being destroyed

33
Convergent Plate BoundariesExamples
Mount Fuji, Japan
Mount Lassen, California
Andes, South America
34
Plate BoundariesTransform

• Crust is neither created nor destroyed

• Plates slide past one another

35
Transform Plate BoundariesExamples
San Andreas Fault
Calexico, California
Carrizo Plains, Central California