1. The Changing Face of the Planet

2. Earth’s Interior Information gathered about the Earth’s interior
comes from direct evidence from rock samples
and indirect evidence from seismic waves
Rocks from inside the Earth, as well as those ejected during volcanic eruptions, give geologists clues about Earth’s interior
Earthquakes produce shock waves that travel through the Earth
Changes occur in the movement of seismic waves due to differences in the structure and makeup of the Earth’s interior
Scientist have determined what the interior looks like by monitoring the path and speed of seismic waves

3. The Earth’s Interior
The four layers of the Earth are the crust, mantle, inner core and outer core
These layers vary greatly in size, composition, temperature, and pressure

4. The Earth’s Crust The crust is the Earth’s outermost layer
Made up of three types of solid rock
Thickness varies with type
Oceanic crust (makes up the ocean floor)
Less than 10 Km thick
Consists mostly of basalt
Continental crust (makes up the landmasses)
Average thickness of about 32 Km
Made mostly of granite

5. The Earth’s Mantle Earth’s mantle is made up of rock that
is very hot, but solid
Divided into layers based on the physical characteristics of those layers
Extends to a depth of about 3000 Km below the surface
Contains about 80% of the volume of the Earth and 68% of its mass
Made mostly of the elements silicon, oxygen, iron, and magnesium
Density increases with depth

6. Divisions of the Earth’s Mantle
Mohorovicic discontinuity (Moho)- Boundary separating the crust from the mantle
Lithosphere-
Topmost solid part of the Earth
Composed of the crust and part of the upper mantle
Broken into large sections called plates
Asthenosphere-
Located directly beneath the lithosphere
A hot weak zone, capable of gradual flow
Rock in this portion of the mantle can flow
like a thick liquid (Has plasticity)
Lower mantle-
Zone of solid rock, located directly beneath
the asthenosphere, and extends to the core

7. The Earth’s Core
The Earth’s core is subdivided into two layers, and inner and outer core
Both layers are composed mostly of the metals iron and nickel

8. The Outer and Inner Cores
Outer Core- Layer of the molten metal surrounding the inner core
High temperatures keep the iron and nickel in the outer core molten
Inner Core- Dense ball of solid metal found at the Earth’s center
Intense pressure causes the particles of iron and nickel to remain solid
The inner core rotates within the outer core

9. The Core & Earth’s Magnetic Field
Scientists think that convection
currents in the liquid outer core
create Earth’s magnetic field
The magnetic field helps
protect our planet from
the Sun’s solar winds

10. The Earth’s Changing Interior
It is believed that the Earth was not originally layered, the divisions we see today formed slowly over time
Shortly after the Earth was formed, the decay of radioactive elements, along with heat released by colliding particles, produced melting in the planet’s interior
Melting allowed the heavier elements (iron & nickel) to sink toward the center, while lighter, rocky components floated upward
Still occurs today on a smaller scale

11. Plate Tectonics
Theory which links the concepts of Continental Drift and Sea-floor Spreading to explain how the Earth has evolved over time
Helps to explain the formation, movements, collisions, and destruction of Earth’s outer layers
Helps people understand the geologic past and predict its future

12. Evidence for Plate Tectonics
Continental Drift
Location of volcanoes,
earthquake belts and mountains
Sea-floor Spreading
Paleomagnetism

13. Continental Drift Proposed in 1910 by Alfred Wegener
States that the continents were once joined together as a super-continent called Pangaea and have since drifted apart
Since Wegener could not explain why the continents would move, his theory was originally rejected

14. Evidence for Continental Drift
Shape of the continents
Similar fossil deposits on continents thought to have been joined
Rock formations that end at the edges of continents
Glacial deposits (evidence of past climates)
Distinctive rock types

15. Location of the world’s volcano, earthquake belts, and mountain ranges
Most volcanoes, earthquakes, and mountain ranges are found along plate boundaries (places where one plate moves relative to another)
Produced by stresses that build up along the boundaries
As stresses become too
great, fractures form and
earthquakes occur
Fractures allow magma
from the asthenosphere to
reach the surface, forming
volcanoes
Bending and folding of the Earth’s
crust can create mountain ranges

16. Sea-floor Spreading
Sea-floor spreading- Process in which old ocean floor is pushed away from a mid-ocean ridge by the formation of new ocean floor
As the ocean floor spreads, landmasses on either side move apart
Occurs at divergent boundaries (also called spreading centers)
Younger rocks are found closer to the spreading center
The further you go from the spreading center, the older the rocks become
The same pattern of rocks are found on both sides of the center

17. Paleomagnetism
Paleomagnetism- Study of the alignment of magnetic particles in ancient rocks
Provides proof for sea-floor spreading and a means of determining how the continents have moved
When magma cools, grains of iron line up with the magnetic pole (like little compasses)
Polarity reversals occur in parallel bands on opposite sides of the mid-ocean ridges
During the past 4 million years, the magnetic poles have reversed themselves 9 times

18. Theory of Plate Tectonics
States that the topmost solid part of the Earth is divided into rigid plates that move resulting in earthquakes, volcanoes, mountains, and the redistribution of landmasses
Lithospheric plates are made of a thin layer of crust above a thick layer of rigid mantle rock
Usually contain both oceanic and continental crust
Seven major plates, each named after its surface features
Plates move at different speeds and in different directions

19. Earth’s Tectonic Plates

20. Plate Boundaries There are three basic types of plate boundaries
Divergent- moving apart
Convergent- moving together
Transform fault- sliding past each other

21. Divergent Boundaries Plates move apart (diverge)
Also called spreading centers or constructive boundaries
New rocks are formed as older rocks are pushed aside (Lithosphere is created)
Examples: Mid-Atlantic Ridge, East Pacific Rise, and the Great Rift Valley in Africa

22. Convergent Boundaries
Occur where two plates move towards each other
Also called destructive
boundaries
Lithosphere is destroyed
There are three types

23. Types of Convergent Boundaries
Convergent boundary where
two continental plates collide
Forms a single larger continent (India & Asia)
Causes the lithosphere at the boundary to be pushed up, forming a mountain range
Ex.: Himalayas, Urals, & Appalachian Mtns.

24. Types of Convergent Boundaries
Convergent boundary where two oceanic plates
collide
One plate subducts (goes under) the other plate
Also called a subduction zone
Forms a chain of volcanic islands on the overriding plate and a deep sea trench where the plates meet
Ex.: The Mariana Islands and the
Mariana Trench are formed
where the Pacific Plate subducts
under the Philippine Plate

25. Types of Convergent Boundaries
Convergent boundary where an oceanic and a continental plate
collides
The oceanic plate subducts under the continental plate
Forms a chain of volcanic mountains on the continental plate and a deep sea trench along the edge of the continent
Ex.: Along the west coast of
South America, the Nazca Plate
subducts under the South
American Plate, forming the
Andes Mtns. And the Peru-Chile
Trench

26. Transform Fault Boundaries
Also known as strike-slip or sliding boundaries
Plates grind together as they try to slip past each other horizontally causing stress to build up
Earthquakes occur when the stress is released
Examples:
The San Andreas Fault in California,
is a result of the North American Plate
and the Pacific Plate trying to slide past
each other
Transform fault boundaries connect
portions of the mid-ocean ridge system
that are moving at different rates

27. Why the Plates Move
Convection currents within the asthenosphere are thought to be the driving force behind plate movement
Convection current- the movement of material caused by differences in temperature
Hot magma rises to the surface, pushing the older rocks aside and driving the plates apart (occurs at divergent boundaries)
Cooler, denser currents sink
back into the mantle, pushing
the plates together (occurs at
convergent boundaries)