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Do now: Read 4.2 Objectives: You will learn to explain seafloor spreading. You will learn to recognize how age and magnetic clues support the theory of seafloor spreading. - invention of echo-sounding ____________________ devices allowed the construction of accurate maps of the ______ ocean floor - using sound waves, researchers underwater system of discovered an ___________ ridges or __________, mountains and valleys _______, continents like those found on the ____________ Harry Hess proposed this - Early 1960s: __________ theory magma from Earth’s - the idea that _______ mantle rises to the surface at mid_______ ocean ridges and cools to form new seafloor which new magma slowly ________, pushes away from the ridge __________________ ____________ - there were no rocks older than 180 million years, however, some ___________ ___________ continental rocks are almost _________ 4 billion years old - youngest rocks were at mid-ocean ridges _________________ - age of rocks became ______ older farther from the ridges on both sides - magnetic data is recorded by a magnetometer ______________ ocean floor showed - rocks on the ______ magnetic reversals - the magnetic alignment of the rocks reverses back and forth in strips parallel to the mid-ocean ______ ridge ________ LET’S REVIEW! • The invention of _____________ allowed the construction of accurate maps of the ocean floor. • What are mid-ocean ridges? • Who discovered the idea of seafloor spreading? • What is a trench? When is one formed? • What two pieces of evidence proved the theory of seafloor spreading to be correct? - Read section 4.2 and do questions #1-5 Due Wednesday - Notes Packet due Thursday - Study for 4.2 quiz Thursday