1. Unit 3 Earth Science Sixth Grade
PLATE TECTONICS
AND EARTH'S STRUCTURE
Unit 3
Earth Science
Sixth Grade

3. Plate Tectonics
Chapter 6

5. The Big Idea
Plate tectonics accounts for important features of Earth’s surface and major geologic events.

6. Earth’s Structure Section 1
Key concept---Earth is composed of several layers. The continents are part of the uppermost layer, and they move slowly around Earth’s surface.

7. The Layers of Earth Compositional Layers (this should be a review!)
Crust—made of silicon, oxygen, & aluminum
Mantle– thick middle layer, made of silicon, oxygen, & magnesium
Core—center of the Earth, made mostly of iron.

8. Continental and Ocean Crust
2 types of crust on Earth
Continental
Oceanic
Continental crust is thicker than oceanic crust
Oceanic crust is more dense and has two times as much iron, calcium, and magnesium.
Oceanic crust is HEAVIER than continental crust.
Both types are rocky, and fractured

9. The Physical Structure of the Earth

10. Lithosphere—divided into pieces called tectonic plates
Asthenosphere—very slow flowing rock that allows tectonic plates to move
Mesosphere—even slower flowing rock (lower part of the mantle)
Outer core—liquid iron & nickel
Inner core—solid iron & nickel (between 4,000 degrees C and 5,000 degrees C.

11. Mapping the Earth’s Interior
How do scientists know what the Earth is like inside if they have never drilled down that far?

12. Earthquakes produce vibrations called seismic waves.
Seismic waves travel THROUGH Earth at different speeds.
Seismographs measure the times earthquakes take to travel various distances from an earthquakes center.
seismograph

13. The speed of the seismic wave is affected by the type of material that the waves are traveling through.

14. Continental Drift

15. Restless Continents
Alfred Wegener wrote his hypothesis of continental drift in the early 1900’s

16. Continental drift is the idea that a single large landmass broke up into smaller landmasses to form the continents, which then drifted to their present locations.

17. Evidence for Continental Drift
Fossils from the same plant and animal species are found on continents that are far from each other.
Locations of mountains and similar types of rock.
Past patterns of climatic patterns found in fossil evidence on differing continents

18. Evidence for Continental Drift
If the continents were all once together as Pangaea, it would be required that the rocks found in a particular region of one continent today should closely match in age and type with those in the adjacent position on the adjoining continent. This appears to be the case, and is most obvious in mountain ranges that end on one coast line and continue on a landmass across the ocean. An example of this is the Appalachians in northeastern North America and the mountain ranges in the British Isles and Scandinavia. When these landmasses are reassembled on a map of Pangaea the mountain chains form a nearly continuous belt. The rock types, age and structures all match.

19. The Breakup of Pangaea
Wegener called the single large continent PANGAEA (Greek for “all earth”)
Existed 245 million years ago
135 million years ago Pangaea split into 2 continents: Laurasia and Gondwana.
As continents drifted they collided with each other, which caused landforms such as mountain ranges, volcanoes, ocean trenches, and mid-ocean ridges.

20. Sea-Floor Spreading
Scientists did not believe in Wegener’s theory because of the strength of rock.
Many years after his death scientists found new evidence of forces that moved continents. SEA-FLOOR SPREADING.

21. Mid-Ocean Ridges— A Magnetic Mystery
Mid-Ocean ridges are underwater mountain chains that run
through Earth’s ocean floor.

22. Scientists discovered patterns of magnetism in the sea-floor rocks.
The pattern on one side of the ridge was a mirror image of the pattern of the pattern on the other side of the ridge.

24. Magnetic Reversals— Mystery Solved

25. As rock forms from magma, or molten rock, minerals that contain iron form.
Some of these minerals are magnetic and act like compasses.
When the molten rock cools, these tiny compasses are locked in position in the rock.
After Earth’s magnetic field reverses, new magnetic minerals align in the opposite ways

26. Sea-Floor Spreading

27. At a mid-ocean ridge, magma rises through fractures in the sea floor.
As the magma cools, it forms new rock.
As this new rock forms, the older rock gets pulled away from the mid-ocean ridge.
This process is called SEA-FLOOR SPREADING.
THIS IS HOW CONTINENTS MOVE!!

28. MOVEMENT OF TECTONIC PLATES IN CALIFORNIA

29. Summary
Earth is made up of three layers—the crust, the mantle, and the core—based on chemical composition. Of these three layers, the core is made up of the densest materials. The crust and mantle are made up of materials that are less dense than the core.
Earth is made up of five layers—the lithosphere, asthenosphere, mesosphere, outer core, and inner core—based on physical properties.
Knowledge about the layers of Earth comes from the study of seismic waves caused by earthquakes.
Wegener hypothesized that continents drift apart from one another now and that they have drifted in the past.
Magnetic reversals that occur over time are recorded in the magnetic pattern of the oceanic crust, which provides evidence of sea-floor spreading and continental drift.
Sea-floor spreading is the process by which new sea floor forms at mid-ocean ridges.