How does sea floor spreading create a new ocean floor?
The oceanic crust is thin and hot at the mid-ocean ridges where plates are pulling apart from each other. The bouyancy of magma causes it to rise and fill in the gap being created from the separating plates. The basaltic rock being created from the cooling of the magma becomes part of the crust/ocean floor. The rate of spreading is slow in human terms–about the rate of fingernail growth, but in geologic time, its fast enough to move plates all over the planet in relation to each other. Oh, and at the opposite end, oceanic crust is being swallowed up by the mantle, all part of one big conveyor belt.
