Plate Tectonics

Continental Drift All continents were once connected in one land mass called Pangea. Pangea broke apart and continents moved to their current locations

Evidence of Pangea Puzzle-like fit of the continents Similar fossils found on different continents Remains of warm weathered plants in Arctic areas, glacial deposits in tropical areas Similar rock structures found on different continents

Seafloor Spreading Mid-oceanic ridges found in many oceans Hot, less dense material below crust rises upward to the surface at these ridges. It flows sideways spreading away from the ridge As magma moves up it cools and forms new seafloor.

Evidence for seafloor spreading Youngest rocks are found closest to the ridges Reversals of the earth’s magnetic field are recorded in lines parallel to the ridges.

Plate Movements Earth’s crust and upper mantle are broken into segments. ( Lithosphere) These plates move on the plastic-like surface of the mantle. The plastic-like layer of the mantle is called the asthenosphere.

Plate boundaries Plates moving apart - divergent boundaries Plates moving together – convergent boundaries Denser plates sink under less dense plates Newly formed magma is forced upward to form volcanic mountains

Plate collision Plates of same density crumble up to form mountain ranges. Himalayas Earthquakes are common in these areas Plates can also slide past each other forming transform boundaries. Ex San Andreas fault in California Earthquakes are also common in these areas.

Cause of plate movement Plates move on convection currents inside the mantle.

Earthquakes Earthquakes are large vibrations that move through rock and other materials

Elastic rebound When rocks strain and break, then the broken pieces snap back. Rocks deform slowly over time Potential energy builds in the rocks Energy is suddenly released when the rocks break and move The movement causes vibrations to move through the earth

Faults A fault is the surface of a break in a rock. Normal fault- caused by tension forces, rock above the fault moves down compared to rock below the fault Reverse fault- caused by compression forces, rock above the fault moves upward Strike-slip fault- caused by shear forces, rocks on either side of the fault move past eachother.

Seismic Waves When rocks move seismic waves travel away from the fault in all directions. Focus- the point inside the earth where movement along the fault first occurs Epicenter- Point on the surface of the earth just above the focus.

Wave types Primary waves- cause rock to move back and forth in the same direction as the waves are traveling Secondary waves- cause rock to vibrate at right angles to the wave Surface waves- Slowest, largest, and most destructive waves.

Seismograph Seismograph is an instrument that measures and records an earthquakes vibrations The arrival times of the seismic waves are recorded and the epicenter is located Richter scale- measure of an earthquakes intensity. Uses the amplitude of the seismographic waves.

Destruction Modified Mercalli intensity scale- measures the intensity of an earthquake based on structural and geologic damage Tsunamis- When an earthquake occurs on the ocean floor powerful waves are produced that can travel thousands of kilometers

Seismic-safe structures Many high rise buildings stand on huge steel and rubber springs Underground water and gas pipes are replaced with pipes that will bend. Highways have cement pillars with spiral reinforcing rods around them.

Volcanoes Molten rock or magma is forced upward toward the Earth’s surface. The magma and gases spew out to form cone shaped volcanoes. As magma flows onto Earth’s surface through a vent it is called lava.

Some volcanoes are formed where plate collide.