Answer:
The oceanic crust is formed by partial melting of the mantle at mid-ocean ridges. The continental crust is formed even more cycles of partial melting over time, resulting less dense rocks.
Explanation:
The mantle, oceanic crust, and continental crust all have different compositions due to a process called partial melting.
This is where you start to melt a rock, but don´t melt it all the way.
When you partially melt a rock, certain chemical elements tend to stay in the solid rock while others tend to go into the melted part.
As a result, the rock that forms from that melt is less dense than the original rock.
If you then partially melt that rock, you get a rock that is even lighter.
