Here's why:

* Continental Crust: Continents are made of continental crust, which is thicker and less dense than oceanic crust.

* Granite Composition: Granite is a light-colored, coarse-grained igneous rock that is rich in silica, feldspar, and quartz. These minerals give it its characteristic light color and low density.

* Formation: Granite is formed deep within the Earth's crust, typically through the slow cooling and crystallization of magma.

* Continental Growth: Over millions of years, the process of plate tectonics and volcanic activity has resulted in the formation of large amounts of granite, which form the foundation of continents.

While other rocks like sedimentary and metamorphic rocks are also found on the continents, granite forms the majority of the bedrock that makes up the continental crust.