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. Paleozoic Era. Ring of Fire. Media Credits The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit. Media If a media asset is downloadable, a download button appears in the corner of the media viewer.
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How far down in the ocean have we gone? At what depth will water crush you? How deep can a human dive before being crushed? How deep in the ocean can a human go? New oceanic crust is continuously being formed as magma upwells at mid-ocean ridges. The characteristics of oceanic crust hold clues about its age and the environment in which it formed.
A recent article in Reviews of Geophysics synthesized data on oceanic crust from many different studies globally, comparing age and spreading rate. Here, one of the authors gives an overview of what we know about oceanic crust and suggests where additional research is needed. This crust was formed many millions of years ago and has subsequently been moved by tectonic forces and eventually ended up above sea level where researchers can examine it in detail. On the other hand, a vast amount of oceanic crust remains underwater.
However, to date, there have only been a few isolated drill holes, and these have only penetrated part way into the oceanic crust. Thus, much of our knowledge about the structure and composition of oceanic crust and the processes of its formation comes from ophiolites.
How else can we learn about the characteristics of oceanic crust? Seismic waves are sent down into the crust and a signal bounces back. Since the earliest studies, the challenge for scientists has been to correlate the layers seen in seismic profiles with known physical rock characteristics observed from ophiolites and drilling so that layer boundaries, such as between dikes and gabbros, can be mapped throughout the ocean basins.
At fast-spreading ridges magma supply is relatively constant and produces a uniform crust, while at slow-spreading ridges magma supply is more ephemeral and produces a heterogeneous crust.
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