Earth Science
Plate Tectonics
Seafloors: Characteristics and Spreading
Study Tip
Using what you know from plate tectonics, come up with your hypothesis of why seafloor spreads. Then, compare yours to the one by Harry Hess.
Studying the Seafloor
These are ways scientists learn about the deep ocean:
- Seafloor bathymetry: scientists used to drop a line over the side of ships. Now they use echo sounders, which have been used to map the entire seafloor
- Sampling remotely: take samples from different depths to contrast ocean chemistry
Study Tip
Using what you know from plate tectonics, come up with your hypothesis of why seafloor spreads. Then, compare yours to the one by Harry Hess.
- Submersibles: samples of seawater and rocks collected by scientists in submersibles
- Remotely operated vehicles: used to study the seafloor in a safe way
Seafloor Features
Here are some of the major features of seafloors:
- Mid-ocean ridges: underwater mountain ranges that rise miles from the deep seafloor
- Rift zones: zones in the middle of mid-ocean ridges that are lower than the mountain ridges around them
- Deep sea trenches: depressions usually several miles deep located on the edges of continents near active volcanoes
- Abyssal plains: underwater plains, some dotted with volcanoes
More than a quarter of the ocean basin consists of continental margin, which is a transition from continental crust to oceanic crust (“land” to “deep sea”).
Magnetic Evidence on the Seafloor
Magnetic polarity is present within the seafloor. Using a magnetometer, scientists were able to plot symmetrical striped patterns using points of normal and reverse polarity. These patterns revealed that:
- Stripes of normal and reverse polarity alternate across the ocean
- Stripes form mirror images on either side of mid-ocean ridges
- Stripes abruptly end at the edges of continents, sometimes at deep sea trenches
Example of striped pattern formed by points of polarity. Notice how the polarity continues to constantly reverse across the seafloor.
