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Earth Science Notes Seafloor Spreading PT and Seafloor Spreading • The PT Theory was not accepted at first because there was no explanation for how the continents moved. – Scientist did not know yet about convection cells or the information we discussed in our last lecture. • After a while, evidence began to mount for seafloor spreading. This provided an explanation for what moved the continents. Evidence for Seafloor Spreading: Magnetic Reversals • During World War II, sensitive instruments called magnetometers were developed to help detect steel-hulled submarines. When research scientists used magnetometers to study the ocean floor, they discovered a surprising pattern. Measurements of magnetic variations showed that, in many areas, alternating bands of rocks recording normal and reversed polarity were arranged symmetrically about midocean ridges Evidence for Seafloor Spreading: Magnetic Reversals • Magnetic Reversals – The Earth has a magnetic north pole and a magnetic south pole. – These poles have flipped periodically in Earth’s past. • This means the north pole has become the south pole and vise versa. – The record of the reversal of the magnetic field is preserved in magnetic rocks which lie along the ocean floor. Evidence for Seafloor Spreading: Magnetic Reversals • Magnetism in the Earth is created by – Magnetic material – Currents • A bar of iron can be made into a magnet by wrapping it with wires and running a current through the wires. Evidence for Seafloor Spreading Evidence for Seafloor Spreading Evidence for Seafloor Spreading: Age of Rock • Rocks samples taken near the Mid-Ocean ridges show that rock to be the youngest on Earth. • Rocks increase in age as the get farther away from the mid-ocean ridges. Evidence for Seafloor Spreading: Age of Rock Evidence for Seafloor Spreading Summary Lets talk about the main points of what we just discussed.