The till layers deposited by retreating continental glaciers are punctuated by layers of soil that include plant and animal remains that indicate a warmer climate. This pattern is echoed in marine fossils of the same age. Layers are dated by radioactive age dating techniques.
Ocean waves get their energy from surface wind.
The waves are surface waves, and the circular motion disappears at a depth called the wave base. This orderly picture breaks down when the waves get to shallow water. In shallow water, the water motion is retarded at the bottom by friction with the bottom sediment. The tops of the waves, unaffected, begin to lean forward, finally breaking in a surf zone. Wave erosion happens most ferociously at any headlands that poke out into the sea.