Final answer:
The Pacific Coast, affected by the tectonic movements of the Pacific and North American plates, experiences geological activity like ocean ridge spreading, which reshapes the region over time. The spreading rates of ocean ridges can be determined by comparing seafloor ages.
Step-by-step explanation:
The question refers to the geological activity occurring along the Pacific Coast, which comprises coastal regions of California, Oregon, Washington, and parts of British Columbia, as well as the Gulf of California. This region is part of the Ring of Fire and is known for its seismic activity due to the movement of tectonic plates, notably the Pacific and North American plates.
The spreading mentioned in the question happens at tectonic plate boundaries, where plates move apart from one another and a new crust is formed. For example, the San Andreas Fault is a major geological fault in California, signalling the boundary between the Pacific Plate to the west and the North American Plate to the east. Here, the Pacific Plate is moving northward, essentially reshaping the coast over time.
When comparing seafloor ages between the mid-Atlantic Ocean and the Pacific Ocean, scientists can determine spreading rates by measuring the distances across the newly formed crust. The ridge that is spreading faster will show wider bands of young crust in the same time frame. In the case of the Mid-Atlantic Ridge, one can measure the distance from the easternmost tip of South America to the western curve of Africa to calculate the spreading rate in millimetres per year (mm/yr).