Put the steps of seafloor spreading in order from the beginning (#1) to the end (#4) Magma cools and hardens to form new crust.

Magma is forced up towards the crust.

The crust eventually falls into trenches and is recycled back to magma.

Rock is pulled apart and magma fills the gap.

1. Magma is forced up towards the crust.

2. Rock is pulled apart and magma fills the gap.

3. Magma cools and hardens to form a new crust.

4. The crust eventually falls into trenches and is recycled back to magma.

Explanation:

When there is a more than usual activity at a particular place in the mantle, it results in more pressure and magma to be pushed toward the surface. As this process goes on, gradually, the tectonic plate above it gets ripped apart as the magma progresses, breaks through, and pushes them away. The gap is constantly growing, so the magma continuous to come out constantly.

Because the magma, in this case, comes out on the seafloor, it hardens very quickly in the water, creating new rocks, thus new oceanic crust. As new crust is constantly formed, the one formed earlier is pushed to the sides and over the course of tens or hundreds of millions of years, it will come in a situation to be involved in a convergent plate boundary where it will subduct in a trench and will gradually melt and get recycled by the magma in the mantle.