Objectives: TLW…identify different plate boundaries. TLW…explain what happens when plates move apart. TLW… determine how to measure the direction and speed of plates. TLW…model the magnetic reversal of Earth’s poles in an experiment.

Main Ideas:Supporting Details: A. Tectonic plates have different boundaries 1. divergent boundary 2. convergent boundary 3. transform boundary A plate boundary is where the edges of two plates meet. Scientist has discover three boundaries which are: a) divergent boundary b) convergent boundary c) transform boundary Occurs where plates move apart and are found in the ocean. Occurs where plates push together Occurs where plates scrape past each other

Main Ideas:Supporting Details: B. The sea floor spreads apart at divergent boundaries 1. Rift Valley C. Mid-Ocean Ridges and Rift Valleys divergent boundaries are also called spreading centers. Mid-ocean ridge mark sites where the ocean floor is spreading ridges continue to widen, a gap Mid-ocean ridges are the longest chain of mountains on Earth World’s longest ridge, the Mid-Atlantic Ridge, runs the length of the Atlantic Ocean

Main Ideas:Supporting Details: D. Sea-Floor Rock and Magnetic Reversals 1. Magnetic reversal Scientist found a surprising discovery about the Earth’s magnetic field when studying the Sea floor rock. Earth’s magnetic field affects the entire planet and the Earth’s geographic and magnetic poles are not in the same place. Earth’s magnetic poles switch places every so often. North becomes South and the South becomes North The poles switching in directions These changes are cause by changes in the Earth’s magnetic field

Main Ideas:Supporting Details: no one knows why these changes happens; however, the Earth’s geographic poles never change places. Sea-floor rock record every magnetic reversal Magnetic reversals line up like stripes in the rock Scientists had further evidence of plate movement. Most recent reversal happened only about 760,000 years ago The oldest reversal happened more than 150 million years ago.

Main Ideas:Supporting Details: E. Continents split apart at divergent boundaries F. Hot spots can be used to track plate movements Continents also spread apart at a divergent boundary. This is when volcanoes form because the rift valley grows wider, the continent begins to split apart. As the rift valley continues to widen, the thinned valley floor sinks lower and lower until it is below sea level. Water from a nearby ocean or river may fill the valley and form a sea or a lake. hot spots are heated rock rises in plumes or thin columns, from the mantle

Main Ideas:Supporting Details: Volcanoes often develop above the plume. Most hot spots occur far from plate boundaries, they offer away to measure plate movement Hot spots generally stays in one place while the tectonic plate above it keeps moving At the hot spot, the heat from the plume partly melts some of the rock in the tectonic plate above it. Plates stays over the hot spot long enough, the rock above it will melt and in time a volcano will form at the surface of the plate. Plate moves slowly over a hot spot

Main Ideas:Supporting Details: when the plate moves on, it carries the first volcano away from the hot spot. Many hot spots provide a fixed point that scientists can use to measure the speed and direction of plate movements.