Almost all the Earth's new crust forms at divergent boundaries, but most are not known because they lie deep under the oceans. These are zones where two plates move away from each other, allowing magma from the mantle to rise up and make a new crust. Divergent boundaries are where the plates move apart. Seafloor spreading is a procces in which the magma creates new land under water and this process takes over millions of years to form a ten foot hill cause the growth ranges from two-ten centimeters per year. The magma is buoyant and creates more ridges and an example of this is Mid-Atlantic Ridge.