Oceanic crust vs continental crust
Earth’s crust is all around us. Actually, it’s the layer we live on.
But did you know that Earth’s crust is composed of oceanic and continental and oceanic crust?
And it turns out that both are very different from each other.
So how are Earth’s crusts different?
Oceanic crust is young geologically
Hidden beneath Earth’s oceans, underwater volcanoes spew out lava at mid-oceanic ridges (rift valleys). Because divergent plates move apart from each other at mid-oceanic ridges, magma flows upwards from the mantle beneath.
When the lava hardens, it becomes dark rock “basalt” and forming new plates. Because divergent plates fills in the gaps with basalt, oceanic crust turns out to be very young geologically. Over time, the plates grow at oceanic crust and older rock is pushed away from mid-oceanic ridges.
When young rock forms at mid-oceanic ridges, older rock beneath the ocean is pushed away. This is why older rock is further away from mid-oceanic ridges.
But the Earth isn’t expanding so it gets destroyed at subduction zones at the opposite ends of the plate. At convergent plate boundaries, it pushes rock into the mantle and melts where they sink down into the mantle.
Continental crust is buoyant and old
Continents do something different than oceanic crust. They are too buoyant to sink compared to the heavier mantle rocks underneath. This is why continental crust floats on the surface of the mantle. Continental crust also consists of the shallow seabed close to shores called continental shelves.
Unlike oceanic crust that has young geological rock, continents can have rocks up to 4 billion years old. For example, continents are composed of igneous, sedimentary, and metamorphic rocks.
Over time, continents bang into each other like a destruction derby. After they collide, they retain scars like mountain ranges. The geology you see rocks can be twisted because of the interaction with other continents. As time passes, weathering and erosion can erase landscapes like a giant eraser.
Continental crust vs oceanic crust
While buoyant continental crust is old geologically, denser oceanic crust is continuously created at mid-oceanic ridges. This means that the youngest rock on Earth is under the oceans.
Continents float on the surface of the mantle. In fact, the whole lithosphere sits on the plasticky asthenosphere layer that acts like a fluid.
But oceanic crust goes through a cycle of creation at divergent plates and destruction at convergent plates.