4. Evidence for sea floor spreading Since the Earth was formed the north and south poles have periodically “________ ____”. When tectonic plates move apart and _____ fills the gap the iron particles in the magma orientate themselves in line with the Earth’s ________ field. This means that the rock formed on the sea floor contains a “magnetic __________” of the changing field: These magnetic patterns can be used to prove that sea floor spreading does happen, and at a rate of about 2 to 10 cm per _____. Words: impression, magma, swapped over, magnetic, year
5.
6. How far does the Atlantic spread in a lifetime? (100 years) How far has it spread in all of human history? (10 000 years) How far has it moved in 100 million years?
7. Review Radioactive Decay Continental plate Magnetic reversal pattern Earthquakes Subduction High Density Fossils Oceanic Plate Rock types S America Africa Tectonic plates Low density Heat Core Mantle Crust
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