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.
Buy what’s the difference between oceanic and continental crust?
Read more to find out.
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 from oceanic crust. If you know Earth’s density, 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.
For example, the boundary along the African plate and the South American plate is divergent. This means that this oceanic trench in the Atlantic Ocean has some of the youngest rocks on Earth.
Let’s dig a bit deeper into Earth’s geology
Today, you’ve learned that Earth is covered with both oceanic and continental crust. While oceanic crust is mostly young igneous rocks, continental crust is old and buoyant.
Our dynamic planet a remarkable place. We’re learning new things about it everyday. If you want to dig a bit deeper into the geology of Earth, check out these hand-picked articles.
Like a stack of pancakes, younger rock layers pile on top of older layers. We use the law of superposition to reveal Earth’s age and Grand Canyon geology. How old is the Grand Canyon?
If you went 200 million years back in time, Earth was 1 supercontinent. Now, it’s made up of 7 separate continents. If you could fast-forward 250 million years in the future, it will re-assemble into another supercontinent called Pangea Ultima. This is the supercontinent cycle at work.
If you could speed up time, you would see rocks cycling from within the planet. Like a well-oiled machine, rocks are igneous, sedimentary and metamorphic.
Be the first to comment