1. Section 2 Seafloor Spreading
Chapter 17
Section 2
Seafloor Spreading

2. Technology/Ocean Topography
Sonar uses sound waves to measure ocean depth
Magnetometer – device that detects small changes in magnetic fields
Maps showed underwater mountain chains, ocean ridges, and deep sea trenches.

3. Ocean Rocks and Sediments
The ages of rocks in the seafloor vary in different places in a predictable way
Oldest part of seafloor = 180 million y/o
The thickness of ocean floor sediment is less than expected
Age of oceanic crust increases with distance from a ridge; Sediment thickness increases with distance from a ridge

4. Magnetism
Earth’s magnetic field is caused by molten iron in the outer core; a compass
Describe magnetic reversal
The study of plaeomagnetism led to the development of the magnetic polarity time scale
The oceans crust is mostly balsaltic rock; form stripes along the ocean floor parallel to ocean ridges

5. Magnetism
Isochron maps are imaginary lines ona map that shows points on Earth with the same age.
Young crust near ocean ridges and older crust near deep seas trenches

6. Seafloor Spreading
Seafloor spreading is the theory that explains how new ocean crust forms at ridges and destroyed at trenches
This is Wegener’s missing link in his explanations of continental drift