Has anyone seen a physical map of the Earth as it would look like if the water was removed? One of the striking features of such a map is Hawaii. First is the Biggest island (Hawaii), then some smaller big islands. Then some smaller islands. Then a series of rather small islands and many, many underwater mountains in a line going on for thousands of miles.
Source:
The long trail of the Hawaiian hotspot
Now everyone should know that features on the earth are moving slowly with respect to each other. It used to be known for completely compelling theoretical considerations, but now these motions can be measured directly with GPS equipment. Plate tectonic theory tells us that there is a hot spot under the ocean floor. As the section of the crust of the earth (a plate) move with respect to this hot spot. Volcanoes form large islands over the hot spot. When island moves away from the hot spot, its volcano dies, and erosion starts to erode the island away. So behind Hawaii, there is a long string of long extinct volcanoes which for the most part no longer rise above the oceans surface.
If K-Ar dating is not full of beans (and can be properly applied to this case), we would expect that the farther away one gets from the big island, the older the volcanoes (and extinct volcanoes) will be according to K-Ar. Well here are the results (Kilauea is one of the volcanoes on the big island):
Source:
The Formation of the Hawaiian Islands
Do note that the rate of motion of the plates implied by the above image is consistent with the measured rate of motion of Hawaii.