Earth Science Notes Seafloor Spreading

PT and Seafloor Spreading Recall: The PT Theory was not accepted at first because there was no explanation for how the continents moved. Scientist did not know about convection cells yet. After a while, evidence began to mount for seafloor spreading. This provided an explanation for why continents moved.

Evidence for Seafloor Spreading: Magnetic Reversals During World War II, sensitive instruments called magnetometers were developed to help detect steel-hulled submarines. We use these instruments today to measure earths magnetic fields and to find ferrous materials (like the cannon)

Evidence for Seafloor Spreading: Magnetic Reversals When research scientists used magnetometers to study the ocean floor, they discovered a surprising pattern. Measurements of magnetic variations showed that alternating bands of rocks recording normal and reversed polarity were arranged symmetrically about mid-ocean ridges

Data from magnetometer reading.

Evidence for Seafloor Spreading

Evidence for Seafloor Spreading: 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.

What Creates Earth’s Magnetic Field? The inner core of the Earth is solid – this is due to high pressure keeping it that way. The outer core, a 2,000 km thick layer of iron, nickel, and small quantities of other metals. Lower pressure than the inner core means the metal here is fluid. Convections cells circulate this molten iron. The Coriolis force also influences the movement of this fluid material. The flow of iron generates electric currents, which produce magnetic fields. Charge metal atoms passing through these fields go on to create electric currents of their own. This self-sustaining loop is called the geodynamo.

Magnetic Reversals Some measurements put the magnetic north pole moving at 4 miles a year.

Evidence for Seafloor Spreading Compare the two pictures we see here. Hypothesize about how the East African Rift Valley might look in the distant future.

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