Oceanic crust is the Earth's crust that lies beneath the oceans. Think of it as the ocean floor! It's different from the land you walk on, which is called continental crust.
What's it Made Of?
Oceanic crust is mostly made of a dark-colored rock called basalt. This is a type of volcanic rock, meaning it formed from cooled lava. It's denser than the granite that makes up most of the continental crust. This means it's heavier!
- Key difference: Oceanic crust is thinner than continental crust; usually less than 10 kilometers thick, compared to continental crust which can be 8-70 kilometers thick!
Features of the Oceanic Crust
Just like the land above water, the ocean floor has interesting features:
- Mountains: Underwater mountain ranges called mid-ocean ridges are where new oceanic crust is formed.
- Valleys: Deep valleys and trenches exist on the ocean floor.
- Plains: Large, flat areas also make up parts of the oceanic crust.
How it's Formed
New oceanic crust is constantly being created at mid-ocean ridges. Magma (molten rock) rises from deep within the Earth, cools, and hardens to form new basalt. This process is called sea-floor spreading. As new crust forms, older crust moves away from the ridge.
(References: The provided text mentions that oceanic crust is the outermost layer of Earth's lithosphere found under the oceans and formed at spreading centers on oceanic ridges. It also states that oceanic crust is primarily composed of mafic rocks (sima) and is thinner than continental crust (sial). National Geographic Kids mentions that the layer beneath the ocean bed is made of oceanic crust, which is primarily basalt, and that oceanic crust is thinner than continental crust).
