Radiolarian evidence consistent with spreading of the pacific floor.

In sediments west of the East Pacific Rise between the equator and 20 degrees N, Eocene microfossils are recorded no farther east than 134 degrees W; Oligocene, no farther east than 125 degrees W; while Miocene and Pliocene occurrences extend closer to the crest of the rise. This distribution may result from post-Eocene spreading of the sea floor here averaging about 8 centimeters per year.