How fast does the seafloor spread

Maps and other data gathered during the war allowed scientists to develop the seafloor spreading hypothesis. This hypothesis traces oceanic crust from its origin at a mid-ocean ridge to its destruction at a deep sea trench and is the mechanism for continental drift. During World War II, battleships and submarines carried echo sounders to locate enemy submarines Figure below. Echo sounders produce sound waves that travel outward in all directions, bounce off the nearest object, and then return to the ship.

By knowing the speed of sound in seawater, scientists calculate the distance to the object based on the time it takes for the wave to make a round-trip. During the war, most of the sound waves ricocheted off the ocean bottom. This echo sounder has many beams and creates a three dimensional map of the seafloor. Early echo sounders had a single beam and created a line of depth measurements. After the war, scientists pieced together the ocean depths to produce bathymetric maps, which reveal the features of the ocean floor as if the water were taken away.

Even scientist were amazed that the seafloor was not completely flat Figure below. The major features of the ocean basins and their colors on the map in Figure above include:. When they first observed these bathymetric maps, scientists wondered what had formed these features. Maps and other data gathered during the war allowed scientists to develop the seafloor spreading hypothesis. This hypothesis traces oceanic crust from its origin at a mid-ocean ridge to its destruction at a deep sea trench and is the mechanism for continental drift.

During World War II, battleships and submarines carried echo sounders to locate enemy submarines. Echo sounders produce sound waves that travel outward in all directions, bounce off the nearest object, and then return to the ship. By knowing the speed of sound in seawater, scientists calculate the distance to the object based on the time it takes for the wave to make a round-trip.

During the war, most of the sound waves ricocheted off the ocean bottom. This animation shows how sound waves are used to create pictures of the seafloor and ocean crust. After the war, scientists pieced together the ocean depths to produce bathymetric maps, which reveal the features of the ocean floor as if the water were taken away.

Even scientist were amazed that the seafloor was not completely flat. What was discovered was a large chain of mountains along the deep seafloor, called mid-ocean ridges. Scientists also discovered deep sea trenches along the edges of continents or in the sea near chains of active volcanoes. Finally, large, flat areas called abyssal plains we found. When they first observed these bathymetric maps, scientists wondered what had formed these features.

In other cases, oceanic crust encounters a passive plate margin. Passive margins are not plate boundaries, but areas where a single tectonic plate transition s from oceanic lithosphere to continental lithosphere. Passive margins are not sites of fault s or subduction zone s. Thick layers of sediment overlay the transitional crust of a passive margin.

The oceanic crust of the Mid-Atlantic Ridge, for instance, will either become part of the passive margin on the North American plate on the east coast of North America or the Eurasian plate on the west coast of Europe. New geographic features can be created through seafloor spreading. The Red Sea, for example, was created as the African plate and the Arabian plate tore away from each other.

Eventually, geologist s predict, seafloor spreading will completely separate the two continent s—and join the Red and Mediterranean Seas.

Mid-ocean ridges and seafloor spreading can also influence sea level s. As oceanic crust moves away from the shallow mid-ocean ridges, it cools and sinks as it becomes more dense. This increases the volume of the ocean basin and decreases the sea level. For instance, a mid-ocean ridge system in Panthalassa—an ancient ocean that surrounded the supercontinent Pangaea —contributed to shallower oceans and higher sea levels in the Paleozoic era.

Panthalassa was an early form of the Pacific Ocean, which today experiences less seafloor spreading and has a much less extensive mid-ocean ridge system. This helps explain why sea levels have fallen dramatically over the past 80 million years.

Seafloor spreading disproves an early part of the theory of continental drift. Supporters of continental drift originally theorize d that the continents moved drifted through unmoving oceans. Seafloor spreading proves that the ocean itself is a site of tectonic activity.

Seafloor spreading is just one part of plate tectonics. Subduction is another. Subduction happens where tectonic plates crash into each other instead of spreading apart. At subduction zones, the edge of the denser plate subduct s, or slides, beneath the less-dense one.

The denser lithospheric material then melts back into the Earth's mantle. Seafloor spreading creates new crust. Subduction destroys old crust. The two forces roughly balance each other, so the shape and diameter of the Earth remain constant. Earth's newest crust is created at sites of seafloor spreading—red sites on this map. Map courtesy NOAA. Triple Junctions. Also called the geosphere. Mid-Atlantic Ridge.

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