The Pacific Ocean is by far the world’s largest ocean, more than five times wider than our moon. But why is the Pacific so big?
Covering about 63 million square miles (163 million square kilometers) — more than 30% of Earth’s surface — all of the world’s continents could fit inside the Pacific basin, according to the National Oceanic and Atmospheric Administration (NOAA). The Pacific, which holds more than half of the free water on Earth, is also our planet’s deepest water body, extending to a depth of more than 36,000 feet (11,000 meters) at Challenger Deep in the Mariana Trench, NOAA noted.
The predecessor of the Pacific Ocean was Panthalassa, or the Panthalassic Ocean, which was once Earth’s only ocean. This world-spanning superocean existed when all of Earth’s continental land was united in the supercontinent Pangaea.
“Panthalassa was the proto-Pacific,” Susanne Neuer, founding director of the School of Ocean Futures at Arizona State University in Tempe, told Live Science. “The Pacific is essentially what remains of Panthalassa.”
Oceans and continents past and present rest on top of tectonic plates, the giant slabs of rock that make up Earth’s rigid outer shell. These plates are regularly on the move, sometimes colliding into each other, sometimes pulling apart from one another. About 230 million years ago, such motions led Pangaea to start breaking up.
“What became North America and Eurasia began to pull apart from what became South America and Africa and Antarctica and Australia,” Adriane Lam, an assistant professor of Earth sciences at Binghamton University in New York, told Live Science.
Related: Do the Pacific Ocean and the Atlantic Ocean mix?
Eventually, Pangaea split apart. In the gap that emerged between the continents, the Atlantic Ocean was born. “The Atlantic is growing about two to three centimeters each year, or about an inch,” Neuer said. “That doesn’t sound like much, but when you multiply that by millions of years, it’s a lot.”
As the continents making up Pangaea were pushed apart, Panthalassa shrunk. At the “subduction zones” where these continental plates slid over Panthalassa’s oceanic plates, the “Ring of Fire” emerged, a zone infamous for volcanoes and earthquakes surrounding what is now…
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