Here's how it works:

1. Mid-ocean ridges: These are underwater mountain ranges where tectonic plates are pulling apart.

2. Magma upwelling: As the plates move apart, magma from the Earth's mantle rises up into the gap.

3. Cooling and solidifying: The magma cools and solidifies, creating new oceanic crust.

4. Pushing apart: This new crust is pushed away from the ridge as more magma rises, continuing the process of seafloor spreading.

This process is a fundamental part of plate tectonics and plays a significant role in shaping the Earth's surface.