PLATE TECTONICS & CONVECTION

Earth’s Interior

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

What moves the plates?

1. Mantle Convection2. Ridge Push3. Slab Pull

Mantle Convection

What causes these Plates to move?

Convection Currents Demonstration

Mantle Convection

Mantle Convection Convection Current

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!”

REVIEW: Earth is HOT

EARTH’S FORMATIONRADIOACTIVE DECAY OF

ELEMENTSMoving 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.  

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.

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

How Plates Move

CONVECTION CURRENTS IN ASTHENOSPHERE

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

RIDGE PUSH

Human Demonstration - Dominoes

SLAB PULL

Table Cloth Demonstration

Ridge Push

Slab Pull

WHY DOES THE OCEANIC CRUST GO UNDER THE CONTINENTAL CRUST?

Density!!!

Mostly Basalt 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 (10 - 70 km thick) Low Density (2.7 g/cm3)

Oceanic Crust Continental Crust