The Earth's design includes three layers of material: the crust, the mantle and the core. The crust and mantle layers are mostly rocks and minerals while the center is a hot metal core.
Differences in Rock Material
Different types of granite make up the continental crust and scientists often refer to it as "sial," which means silicate and aluminum. It's a bit thicker than oceanic crust, which is made up of layers of basalt. Scientists refer to the oceanic crust materials as "siam," which is silicate and magnesium. Both types of crusts form during plate tectonics, where tectonic plates crash into each other or rip apart to create new layers of rock. The continental crust forms both above and beneath the Earth's surface, helping to create mountain ranges and peaks. The thickest layer of the continental crust is at the top of mountain ranges like the Himalayas.
The difference between oceanic and continental crust rock material is the density and explains why the oceanic crust is beneath the ocean's surface while continental crust can rise into the Earth's atmosphere in the form of mountain peaks. Oceanic crust is the crust layer found beneath the oceans and contains denser rock than the continental crust. Basalt is magma that builds up in time and gets broken down through the process of subduction. As this partial melting process occurs at the mid-ocean ridges, the oceanic crust increases in density. Occasionally, the oceanic crust will get forced upward above sea level, creating ophiolites and allowing scientists the opportunity to gather samples of this otherwise hard-to-reach layer of the Earth's crust.
Continental crust is the layer of the Earth that's readily seen from space. It makes up all of the Earth's continents and is much less dense than the oceanic crust. Due to a lower density, this layer of crust is able to float on the surface of the water. Like the oceanic crust, the continental crust is destroyed by the subduction process but goes through more partial melting processes than the oceanic crust, allowing it to maintain its lower density and remain above the ocean. When a rock goes through a partial melting process, the rock that doesn't melt maintains its original properties while the melted area either recycles or loses some of its original properties, allowing it to maintain the density level.
One big difference between the oceanic crust and the continental crust is the age of the crusts. Although both go through changes during the subduction process, the continental crust is rarely completely destroyed during subduction. The oceanic crust, on the other hand, may completely melt away into rising magma, creating brand new rock. The oldest oceanic crust exists in the Ionian Sea and is only millions of years old as opposed to some rock in Quebec, Canada where the continental crust is estimated at 4 billion years old. Some scientists estimate that some areas of continental crust could be as old as the Earth. This is why scientists study the continental crust to determine the age of the Earth or how long a formation has existed because this layer of crust rarely goes through a total destructive process.