Earth Science Notes Seafloor Spreading PT and Seafloor

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 • 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