1. Plate Tectonics & Convection

2. Earth’s Interior

3. The Theory of Plate Tectonics
Earth’s crust and part of the upper mantle are broken up into plates that move on a plastic-like layer of the mantle
Earth’s surface is made up of rigid plates known as the Lithosphere.
80 km thick (up to 200 km thick beneath continents), very brittle, easily fractures at low temperature.
These plates “float” over the upper mantle called the Asthenosphere.
250 km thick - solid rock, but it is soft and flows easily (ductile).
There are 7 major plates and about 18 minor plates.
Most of the major plates are located under the continents

5. What moves the plates?
Mantle Convection
Ridge Push
Slab Pull

6. What causes these Plates to move?
Mantle Convection
What causes these Plates to move?
Convection Currents Demonstration

7. Mantle Convection Mantle Convection Convection Current Examples
Any movement of matter that results from differences in density
Differences of density within the earth are caused by differences in temperature
Examples
“Lava” in a lava lamp
Boiling Water
Making popcorn in an air popper
“Hot air rises!”

9. RADIOACTIVE DECAY OF ELEMENTS
REVIEW: Earth is HOT
EARTH’S FORMATION
RADIOACTIVE DECAY OF ELEMENTS
Moving objects have kinetic energy. When objects collide, kinetic energy is converted into thermal energy.
When Earth formed, objects in the solar system collided, generating thermal energy.
When the earth was molten, it began to separate into layers based on density. Particles of matter had gravitational potential energy, so as gravitational force acted to separate these particles according to density, the particles experienced friction (because they were moving past one another). A byproduct of friction is thermal energy.
What is radioactive decay?
Some elements have an unstable nucleus
To become more stable, the nucleus of the radioactive element breaks apart
When a nucleus breaks apart, heat is released.
The decay of radioactive elements into more stable elements releases heat inside the Earth, making the interior of the Earth hot
Radioactive elements have been present within Earth since the Earth was formed and still exist within Earth today, therefore, heat continues to be generated in Earth’s interior.

10. Convection Currents
Convection currents transfer heat through the movement of heated fluid material (i.e. molten rock)
The asthenosphere is heated by the inner and outer core of the Earth. This heat is transferred through the mantle.

11. When materials like solid rock are heated, they expand and become less dense
Hot, less dense plastic-like material rises, coming in contact with the lithosphere (crust and uppermost mantle)
It cools at the lithosphere (or Earth’s outermost layer) and becomes more dense causing the material to sink
The constant rotation of the material creates a current that is able to pull the plates

12. How Plates Move
CONVECTION CURRENTS IN ASTHENOSPHERE

13. Forces Causing Plate Motion
Rising mantle material at mid-ocean ridges creates the potential for plates to move away from the ridge
Moves lithosphere in opposite directions away from a mid-ocean ridge
Ridge Push
When tectonic plates collide, the denser plate (slab) will sink in to the mantle
As a slab sinks, it pulls on the rest of the plate with a force called slab pull
Slab Pull

14. Human Demonstration - Dominoes
Ridge Push
Human Demonstration - Dominoes

15. Table Cloth Demonstration
SLAB PULL
Table Cloth Demonstration

16. Ridge Push

17. Slab Pull

18. Why does the Oceanic Crust go under the Continental Crust?
Density!!!

19. Oceanic Crust Continental Crust Mostly Basalt Young (0-200 myo)
High in Iron (5-10%)
Low in Silica (45-60%)
Young (0-200 myo)
New rock formed at MOR
Thin (8-10 km thick)
Dense (3.0 g/cm3)
Mostly Granite
Low in Iron (2-5%)
High in Silica (65-75%)
Sits on top of Oceanic
Old (up to 4 byo)
Thick ( km thick)
Low Density (2.7 g/cm3)