Plate Tectonics

• The surface of the earth
The surface of the earth is in constant movement.
The present features of earth come from its ongoing history. After the sun was formed, matter cooled creating the planets. The continents were once joined (Pangaea).

• Layered structure of the earth

Crust: surface layer of mainly basalt or granite, 5 to 25 miles thick

Mantle: 1,800 miles thick, rock of intermediate density, moves very slowly, a solid metal (mostly Magnesium) that is so molten, so melted that it moves like a liquid

Outer core: liquid iron and nickel  1400 miles thick
Inner core: solid iron and nickel, 800 miles thick, about 7,000 degrees C

• Crust movements
The surface of earth is made up of rigid plates that are in constant motion.
Plates move because molten rock rises and falls under the crust causing slowly flowing currents under the plates --AND WE WILL DISCUSS CONVECTION CYCLES IN GENERAL.
Plates move at speeds ranging from 1 to 4 inches (5-10 centimeters) per year. Earthquakes usually occur where stress has been built up by plates moving in opposite directions against each other. Earthquakes cause waves (vibrations) which have:

focus, the point below the surface where the quake begins

epicenter, the point on the surface above the focus
Severity of ground shaking is measured on the Richter scale

• Volcanoes usually occur where plates are pulling apart or coming together, but some occur  at holes (hot spots) in the crust away from plate boundaries. As plates move over these  hot spots, they cause chains of volcanoes and island chains like the Hawaiian Islands.

• Evidence for long-term movement of plates includes fit of continents and matches of rock types, fossils, and structures; ocean floor age and topography; ancient climate zones; locations of earthquakes, volcanoes, and mountain ranges; magnetic directions in ancient rocks.

Some concepts we will explore are:

Compare rapid and gradual changes to Earth’s surface.

1. Describe how energy from the Earth's interior causes changes to Earth’s surface (i.e., earthquakes, volcanoes).
2. Describe how earthquakes and volcanoes transfer energy from Earth's interior to the surface (e.g., seismic waves transfer mechanical energy, flowing magma transfers heat and mechanical energy).
3. Model the process of energy buildup and release in earthquakes.
4. Model how small changes over time add up to major changes to Earth’s surface.