When magma rises to Earth's surface and solidifies during seafloor spreading, it forms new oceanic crust. Here's a breakdown of the process:

1. Magma Rises: At mid-ocean ridges, the Earth's tectonic plates are pulling apart. This creates a gap where hot magma from the mantle rises.

2. Solidification: As the magma reaches the ocean floor, it cools and solidifies, creating new igneous rock called basalt.

3. New Crust Formation: This solidified magma forms a new layer of oceanic crust.

4. Seafloor Spreading: As more magma rises and solidifies, the seafloor is pushed outwards on both sides of the ridge, effectively spreading the ocean floor apart.

This process is a continuous cycle, constantly creating new oceanic crust and expanding the ocean basins. The new crust is always younger than the older crust further away from the mid-ocean ridge.