1. Earth’s History and Structure
View of Earth from moon. We know what the surface of the Earth looks like. What does the inside look like?

2. Do Now
What are the main compositional layers of the Earth?

3. Crust
Mantle
Core

4. Origin of the Earth Earth formed approximately 4.6 billion years ago
Early earth lacked an atmosphere
Meteors and Asteroids bombarded the Earth
Our early Earth grew from a barrage of extraterrestrial impacts, increasing in mass over time. In the early stages of planetary accretion, the Earth was much less compact that it is today. The accretionary process led to an even greater gravitational attraction. Gravitational energy converted into heat. Radioactive elements are unstable, and over time become more stable. Radioactive decay processes releases heat. U-238 to Pb Initial accretion led to a homogeneous sphere that eventually became density stratified with the heavier iron and nickel sinking to the center of the earth, and the lighter silicates (rocky) floated to the top.

5. Meteor Crater Arizona

6. Earth’s Interior Core Mantle Crust Made of Iron and Nickel
Inner Core - solid
Outer Core - liquid
Mantle
Less dense than core
Iron and Silicates
Mostly solid
Core – composed of two parts. The core is very dense and composed mostly of Iron and Nickel. The inner core is solid. This is because there is so much pressure exerted that it can only exist in the solid form. The outer core is liquid iron and nickel. Again, it is very dense but because it is in its liquid form it is less dense than solid and forms the outer core.
Mantle is composed of Iron and Magnesium silicates (Si + O). It is mostly solid, but the uppermost part of the mantle is partially molten (slush – where you do have liquid and solid mixed). Now, this is very important in plate tectonics.
Crust –This is the outermost layer. It is very thin and rigid. Rigid means that it is a solid. If you can imagine an apple. It would have the thickness of the skin of an apple. There is two types of crust – continental crust and oceanic crust.
Important notes:
Thin crust + uppermost mantle is rigid. This forms the “lithospheric plates”.
partially molten mantle acts as a lubricant. This enables the plates to move freely along the surface of the Earth.
Crust
Outermost layer is solid rock.
Continental – granite
Oceanic – basalt

7. Lithosphere The outer solid layer of the Earth Litho- Rock
Sphere- Round

8. Lithosphere Consists of continental, oceanic and upper part of mantle
Continents composed of granite-type rock, less dense then oceanic crust
Oceanic crust formed of basalt; more dense then continental crust
Why do continents sit higher than ocean basins? It is their composition and density. Continent = Quartz (SiO2) and Feldspars (K, Ca, Na, Al, SiO2). These are light elements. Ocean = Basalt (Fe and Mg). These are heavier elements. Asthenosphere is partially molten. It forms a lubricant to allow plates to move.

9. Asthenosphere Located below the Lithosphere Enormous heat and pressure
Rock exhibits Plasticity: ability to flow
Causes Tectonic Plates to move

10. Mesosphere
Located below the Asthenosphere
“Meso” means middle

11. Outer Core
Made of liquid Iron and Nickel

12. Inner Core
Made of solid iron and nickel

13. Do Now
What is the difference between the Earth’s lithosphere and asthenosphere.

14. Earth’s Gravity
Gravity is the force of attraction due to an object’s mass
Determined by mass and distance between two objects in space

15. What is the difference between weight and mass?
Hint: You would weigh less on the moon, but your mass is constant.

16. Weight and Mass Weight-Measurement of the pull of gravity on an object
Mass-The amount of matter an object is composed of

17. Classwork/Homework
Research how the Earth’s magnetic field is generated.
Describe how the magnetic field protects us from radiation.

18. Classwork/Homework Read 29-32 Define all Key Terms
Answer (1-6) on pg. 32

19. Earth’s Interior

20. Continental Drift Evidence
Researchers noted geographic fit of continents
e.g. Africa and S. America
Atlantic formed by separation of Africa from S. America
Seuss, 1885, proposed super continent by studying fossils, rocks, mountains
Wegener and Taylor, early 1900’s, proposed continental drift and Pangaea
Seuss hypothesized a super continent “Pangaea” surrounded by oceans.
Evidence supporting the idea that the continents had drifted.
Geographic fit of continents
Fossils
Mountains
Glaciation

21. Continental Drift Geographic Fit
About 210 Ma, Pangaea began to break apart.
Continents seem to fit together like pieces of a puzzle

22. Continental Drift Fossils
Studies were done on land animals that could not swim. Once continents split, evolution occurs. Organisms begin to differentiate. Climate is different, food sources are different, predators are different.
Similar distribution of fossils such as the Mesosaurus

23. Palisades in North New Jersey

24. Continental Drift Mountains
If you were to put the puzzles back together, mountain chains match up, i.e., Appalachian Mtns, British Isles, and Caledonian Mtns.
Mountain ranges match across oceans

25. Continental Drift Glaciation
Glaciers typically occur near the poles. We are in a warm period, but in the past it was cool and ice caps grew. Deposits related to glaciers were deposited. You also find glacial deposits in Africa near the equator. How to you get glacial deposits near the equator?
Glacial ages and climate evidence

26. Diving between the plates in Iceland

27. Continental Drift Model Problems
Alfred Wegener
Presented research to professionals
Did not provide a plausible mechanism to explain how continents drifted
Wegener was a scientist. Scientists go to scientific meetings to present their research. When Wegener presented his research to other physicists, they did not agree. They wanted to know how do continents drift? There was no driving mechanism to support continental drift. Wegener could not answer “how” so his Continental Drift Model was not accepted.

28. Seafloor Spreading
Continental drift reexamined in 1960’s with new information
New theory developed – Seafloor spreading
Supporting evidence for seafloor spreading
World seismicity
Volcanism
Age of seafloor
The 1960’s is relatively recent. Geology is a new science compared to Physics, Chemistry and even Biology. People were doing separate studies about earthquakes, volcanoes, age of sea floor, paleomagnetism. Someone put it all together. A new theory developed – Seafloor Spreading. There were a lot of evidence to support Seafloor spreading.
Paleomagnetism
Heat flow
Theory combining continental drift and seafloor spreading termed “Plate Tectonics”

29. Seafloor Spreading
The idea of seafloor spreading is that new crust is being formed at spreading centers and old crust is being destroyed in deep trenches. For example, Mid-Atlantic ridge is a chain of underwater mountain chains where new crust is being formed.
New sea floor created at the mid-ocean ridge and destroyed in deep ocean trenches

30. Evidence for Seafloor Spreading World Seismicity
Note: Orange is shallow. At spreading centers, EQ only occur at the surface. At SZ, deep EQ occur, i.e. Japan, Indonesia, Philippines, Aleutians. How does seismic activity support plate tectonics? They occur along plate boundaries.
Earthquake distribution matches plate boundaries

31. Evidence for Seafloor Spreading Volcanism
Where do volcanoes occur? Subduction zones. Why are they associated with subduction zones? Oceanic crust is moving deep into the Earth. Volcanism also occur at hot spots. Where is the tallest mountain? Mauna Loa. Highest elevation? Mount Everest. If you were to take Mauna Loa and place next to Mount Everest, it is the highest mountain. It is measured at its base deep on the ocean floor.
Volcanoes match some plate boundaries; some are hot spots

32. Evidence for Seafloor Spreading Age of Seafloor
Age of Earth is 4.5 Ga. Oldest oceanic crust is only 180 Ma. Why is the ocean so young? Old oceanic plate is being subjected or destroyed.
Youngest sea floor is at mid-ocean ridge
Oldest sea floor away from mid-ocean ridge

33. Evidence for Seafloor Spreading Paleomagnetism
Today, Earth’s magnetic field points to the North. Why? They believe that the magnetic field is caused by the liquid outer core moving around the solid inner core by Earth’s spin. The iron (Fe) content in the core produces a magnetic field. Magnetic field is important to us in that it prevents harmful radiation of the Sun to reach us. Every 700,000 years or so, the Earth’s magnetic field reverses. These reversals are recorded in molten magma. As the magma cools, its iron-rich minerals tend to line up with Earth’s magnetic north.
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 Earth’s surface, they record Earth’s magnetic field (normal or reverse polarity)

34. Evidence for Seafloor Spreading Paleomagnetism
The record of these alternating reverse and normal polarity helps support the idea of seafloor spreading.
Paleomagnetic studies indicate alternating stripes of normal and reverse polarity at the mid-ocean ridge.

35. Seafloor Spreading Heat Flow

36. Seafloor Spreading Convection Currents
Magma was found were new seafloor was being made.
In 1960, proposed as driving force to move continents

37. Theory of Plate Tectonics
Heat flow provided the mechanism to move the lithospheric plates.
John Tuzo Wilson combined ideas of continental drift and seafloor spreading into “Plate Tectonics”

38. Principles of Plate Tectonics
Earth’s 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

39. Plate Boundaries Three types
There are three ways that plates can move relative to each other. They can move apart – divergent plate boundary, they can come together – convergent boundary, or they can slide past one another – transform fault.
Divergent
Convergent
Transform

40. Plate Boundaries Divergent
Plates move away from each other
New crust is being formed

41. Divergent Plate Boundaries Examples
East African Rift
Mid-Atlantic Ocean Ridge

42. Plate Boundaries Convergent
Three Types:
Ocean-continent
Ocean-ocean
Continent-continent
Plates are moving toward each other
Crust is being destroyed

43. Convergent Plate Boundaries Examples
Mount Fuji, Japan
Mount Lassen, California
Andes, South America

44. Plate Boundaries Transform
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Crust is neither created nor destroyed
Plates slide past one another

45. Transform Plate Boundaries Examples
San Andreas Fault
Calexico, California
Carrizo Plains, Central California