Here's a breakdown:

* Mid-ocean ridges are underwater mountain ranges where tectonic plates diverge or move apart.

* Magma (molten rock) from the Earth's mantle rises up through these gaps, cools, and solidifies to form new oceanic crust.

* This new crust is primarily composed of basalt, a dark-colored volcanic rock.

* The lithosphere, which is the rigid outer layer of the Earth, is also formed here. The lithosphere is made up of both the crust and the uppermost part of the mantle.

So, the process of seafloor spreading at mid-ocean ridges creates both new oceanic crust and lithosphere.