First continents

Although we tend to think of continents as being permanent features on Earth, in fact the earliest Earth was devoid of continents.

Basaltic ocean crust formed first, as the early Earth cooled from its original molten state. Continental crust is formed through tectonic plate collisions, which involves the subduction of one plate, recycling the plate back into the Earth’s mantle, causing melting of lighter minerals and migration of this new, granitic magma upward where it solidifies, forming new continental crust.

Continental crust is less dense than ocean crust, and in a plate tectonic collision the lighter continental crust is not subducted but remains at the earth’s surface.

Continents grow by accretion of granitic crust through eons of plate collisions.

This process of continental growth and accretion continues today; much of the state of California is a mosaic of microplates that have been accreted to the west coast of North America.

Illustration from here.