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Evolution of the Pacific Ocean (150 mya - Present)

The Pacific  Ocean is the world's largest ocean, covering nearly one-half of the globe.  Though huge, the Pacific is getting smaller.  It was once much wider when all the continents were joined together in the supercontinent, Pangea. The Pacific ocean basin is getting smaller because the Atlantic Ocean is opening and North America and South America are moving westward.

 Most of the Pacific Ocean is underlain by the Pacific plate.   The Pacific plate is bordered on the east by three  smaller plates, the Nazca Cocos, and Juan de Fuca plates.  The western edge of the Pacific plate is being subducted beneath the Eurasian, Philippine, and Indo-Australian plates.   Subduction along the perimeter of the Pacific ocean produces a great circle of earthquakes and volcanic activity known as the "Ring of Fire".

Though the Pacific Ocean is ancient, the Pacific plate is relatively young.  There probably  has been an ocean in the present-day position of the Pacific Ocean for nearly a billion years.  The Pacific ocean basin first formed when the western half of North America rifted from the eastern coasts of Australia and Antarctica over 750 million years ago (see Rodinia breakup animation).  The rifting of the Precambrian supercontinent, Rodinia,  produced the Panthalassic Ocean (see Late Precambrian paleogeographic map).  The plates that formed the Panthallasic Ocean basin have long been subducted.

The modern Pacific plate was formed nearly 180 million years ago.  It is not clear how the original Pacific rift got started, but the Pacific, Farallon, Kula,  and Izanagi plates rapidly grew.  This animation shows the growth of the Pacific plate. The Kula and Izanagi plates have been completely subducted.  The Nazca, Cocos and Juan de Fuca plates are the remnants of the Farallon plate.  

The Pacific  Ocean floor, shown in rainbow colors according to age, continues to grow along the East Pacific Rise.   Notice how the East Pacific Rise generally stays near the center of the ocean.  Only in the last 30 million years has the northeast part of the East Pacific Rise been subducted beneath North America.  The subduction of this spreading center has caused California and Baja California to rift away from North America and slide northwards.  The subduction of the East Pacific Rise beneath North America has also caused western North America to spread apart forming the Basin and Range.

This animation is available on CD-ROM in Quicktime format.   For more information see Teaching Materials.

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