1. EQ: How has the physical process of plate tectonics effected Earth’s surface? Lesson 20

2. Pangaea Song and Lyrics

3. Effects of Physical Processes
Just as there was once a single great land mass, there was also a single great ocean around that land mass.
The separate oceans we now know were formed as the land masses separated.
These separations produced amazing features on the ocean floor, such as the longest mountain range on Earth.

4. Plate Tectonics Part 1
Many physical processes have shaped Earth’s surface.
The physical process of plate tectonics have shaped Earth’s oceans.
Plate Tectonics describes how Earth’s lithospheric plates move and how their movements shape Earth’s crust.
The continents and ocean floor of Earth ride on 13 lithospheric plates

5. Plate Tectonics, 2
In the 1950s, scientists discovered that rocks on the floor of the oceans were younger than rocks on the continents.
Harry Hess, an American geologist, suggested that the sea floor was spreading. ( Divergent Boundary)
As it spread, from an opening in its middle, magma from Earth’s mantle oozed from the opening onto the surface of the ocean floor.
When the magma came in contact with seawater, it hardened into new rock.

6. Plate Tectonics
This rock formed a huge mountain range that snakes through all of Earth’s oceans.
This undersea mountain range is called the
mid-ocean ridge. ( Divergent Boundary)
As distance from the opening increased, the age of the rocks also increased.
Because the spreading has been constant throughout history, the formation of the South Atlantic Ocean can be traced back to a time when South America and Africa were once part of the same landmass.

7. Continental Divergent
A rift valley is a linear-shaped lowland between two continental plates or mountain ranges that have separated (divergent).

8. A rift valley is formed on a divergent plate boundary.
Location: Africa
Location: Turkey

10. Example of Sea-Floor Spreading

11. Animated Boundaries

12. Convection Currents 1: Causes Plates to Move
Lithospheric plates move due to convection currents in Earth’s mantle.
A convection current is a current formed by heated liquid that moves along a circular path.
Warm liquid moves upward and across a surface because it is less dense.
It cools at the surface, becomes more dense, and moves downward.
Then it warms again, becomes less dense, and moves upward.

13. Boiling Water – Convection Currents

14. Causes of Plate Movement

15. Convention Currents 2: Causes Plates to Move
As long as heat is applied from below, the liquid will move around and around in convection currents
Heat from Earth’s mantle sets up convection currents.
These convection currents are made up of liquid rock.
The liquid rock rises to a place under the lithospheric plates.
The currents move in opposite directions, pushing plates apart in one place, and together in another place.

16. Quick Check Plate tectonics describe movements MAINLY in
A. Earth’s crust.
B. Earth’s mantle.
C. Earth’s outer core.
D. Earth’s inner core.

17. Quick Check
Which ocean was produced by seafloor spreading between Africa and South America?
A. Pacific Ocean
B. Indian Ocean
C. North Atlantic Ocean
D. South Atlantic Ocean

18. Quick Check A. grow younger B. grow older. C. do not change in age.
As distance increases from a mid-ocean ridge, the rocks
A. grow younger
B. grow older.
C. do not change in age.
D. become liquid.

19. Quick Check
Assume a sea floor has been separating at an average rate of 5 cm a year. The sea is presently 8000 km wide. How long ago did the sea begin to form?
A. 1,600 years ago
B. 40,000 years ago
C. 160,000,000 years ago
D. 4,000,000,000 years ago

20. Quick Check A convection current of magma is made up of
A. a rising more dense liquid and a sinking less dense liquid.
B. a rising less dense liquid and a sinking more dense liquid.
C. liquids of the same density.
D. solids of different densities.

21. Quick Check The ancient supercontinent, Pangaea, once contained
all of the Earth’s tectonic plates.
all of Earth’s crust.
C. all of Earth’s continental crust.
D. all of Earth’s oceanic crust