New crust in seafloor spreading comes from magma, which is molten rock found beneath the Earth's surface. Here's a breakdown of the process:

1. Mid-Ocean Ridges: These are underwater mountain ranges where new crust is formed.

2. Magma Upwelling: Magma from the Earth's mantle rises up through the ridges.

3. Cooling and Solidification: As the magma reaches the ocean floor, it cools and solidifies, creating new oceanic crust.

4. Seafloor Spreading: The newly formed crust is pushed away from the ridge as more magma rises and solidifies, a process called seafloor spreading. This process creates new ocean floor and widens the ocean basin.

Essentially, the process of seafloor spreading involves the creation of new crust from molten rock, which is then pushed away from the mid-ocean ridges, causing the ocean basin to expand.