Geology of the Pacific Ocean Geology of the Pacific Ocean The Pacific Ocean evolved in the Mesozoic from the Panthalassic Ocean, which had formed when Rodinia rifted apart around 750 Ma. The first ocean floor which is part of the current Pacific Plate began 160 Ma to the west of the central Pacific and subsequently developed into the largest oceanic plate on Earth. The tectonic plates continue to move today. The slowest spreading ridge is the Gakkel Ridge on the Arctic Ocean floor, which spreads at less than , while the fastest, the East Pacific Rise near Easter Island, has a spreading rate of over
Mid-ocean ridge in past calcite seas, meaning that the Mg/Ca ratio in an organism's skeleton varies with the Mg/Ca ratio of the seawater in which it was grown. The mineralogy of reef-building and sediment-producing organisms is thus regulated by chemical reactions occurring along the mid-ocean ridge, the rate of which is controlled by sea-floor spreading. Mid-ocean ridges are generally submerged deep in the ocean. It was not until the 1950s, when the ocean floor was surveyed in detail, that their full extent became known. The "Vema", a ship of the Lamont-Doherty Earth Observatory of Columbia University, traversed the Atlantic Ocean, recording data