Tectonic Plates Chapter 4

The lithosphere is broken into separate sections called plates. The geological theory that states that pieces of Earth’s lithosphere are in constant, slow motion, driven by convection currents in the mantle is plate tectonics.

Continental Drift Continental drift is the theory that the plates slowly move, and the continents slowly move as a result.

http://www.nature.nps.gov/geology/usgsnps/animate/A06.gif

Types of plate boundaries: 1.) convergent—where one plate sinks beneath another. Oceanic crust is denser and is subducted underneath the continental plate. If both plates are continental or oceanic, the larger plate will be subducted. 2.) divergent—Where plates move away from each other. This occurs near weak spots in the plate caused by rising magma currents. 3.) transform—where two lithospheric plates slide past each other.

Divergent Plate Boundary A rift valley is where the crust stretches until it breaks. An example is the Great Rift Valley in eastern Africa.

Divergent Plate Boundary: Mid-ocean ridge Underwater mountain system that is formed by plate tectonics. Oceanic crust spreads allowing magma to reach the surface and create new ocean floor. http://www.nature.nps.gov/geology/usgsnps/animate/A48.gif

Convergent Boundary A trench forms where two plates collide (subduction occurs) on the ocean floor. The plate that is subducted will then melt and once again become magma.

Mt. Everest-Highest point (29,028 feet) India and Asia collided about 55 million years ago

Mariana Trench – Lowest point (35,800 feet)

A fold is when the squeezing of the continental plates leads to rocks that have been compressed into bends. An example is the Appalachian Mountains.

Transform Boundary Faults are places where rock masses have broken apart and moved away from each other.

Pacific Ring of Fire—25,000 miles—75% of the world’s volcanoes and 90%of the world’s earthquakes

The story of a rock…

Weathering and Erosion Weathering is the breakdown of the materials of rocks into smaller pieces. These smaller particles of gravel, sand, and mud are called sediment.

Water causes weathering What evidence of weathering do you see in this picture?

Wind causes weathering What evidence of weathering do you see in this picture?

Describe how ice causes weathering.

What evidence of erosion do you see in this picture? The process by which water, ice, wind or gravity moves fragments of rock and soil. What evidence of erosion do you see in this picture?

Erosion is Movement of Sediment Erosion carves the Earth's surface creating canyons, gorges, and even beaches. What do you think has caused this rock to look this way?

Fossil Fuels - The energy-rich substances formed from the remains of once living organisms (decayed plant and animal remains from long ago). The 3 major fossil fuels --> Coal, Oil, and Natural gas.