This discovery showed that seafloor increases in age away from the ridges. Therefore, seafloor must form at the ridges, hence the name spreading ridges. Therefore, seafloor must be destroyed at convergent-margin trenches. We like to know how low long things take to happen and the rates of geological processes. For example, magnetic lineations on either side of a spreading ridge.
Absolute velocity is with respect to the mantle.
On Earth, recorded by hot-spot volcanism. All the action takes place at plate margins, while regions away from plate margins are pretty stable. Oceanic vs continental divergent, convergent, transform Know characteristics of various kinds of plate margins. Rio Grande Rift formation of normal faults, horsts and grabens. Example, mid-Atlantic spreading must have started in middle of Pangea continent.