While humans have never known a world without it, the Atlantic Ocean is a relatively new addition to the planet. It started out a smaller lakes and marshlands through the center of a now-scattered supercontinent called Pangea, eventually growing and stretching into the massive body of water we know today. And it’s not actually done growing- every year, a seam down the middle of the Atlantic Ocean, called the Mid-Atlantic Ridge, continues to push outwards, widening the ocean by around two to five centimeters a year. Since the Earth’s circumference isn’t also growing to account for this new land, it got my third grader wondering, “will the Atlantic’s growth squeeze the Pacific Ocean until it’s gone?”
From a human time scale, this may seem like a wacky idea- Oceans don’t just disappear, right? Before geologists had developed the currently accepted model of plate tectonics, the Alfred Wegener’s continental drift model would have probably argued against the total destruction of an ocean. Wegener believed that the major land masses, or continents, on Earth slid around each other and the perimeters of the oceans, as if they were two distinct types of crust on our planet. As we’ve learned more about how our planet’s crust grows and recycles itself, we’ve come to realize that the continents and oceans are built as tectonic plates, and that these units may have boundaries through continents and oceans. This model can then better account for the growth of the Atlantic Ocean, but also for the various points of growth and destruction underneath the Pacific Ocean as well.
We now believe that there are around 12 major tectonic plates, and that they’re all moving relative to each other. As it turns out, the Mid-Atlantic Ridge isn’t the only major expansion taking place right now. The Arabian and African plates are also being pushed away from each other thanks to expansion under the Red Sea in a process that likely resembles the early days of the Atlantic Ocean. Given enough time, it’s thought that Africa will be fully separated from the Middle East as the Red and Mediterranean Seas are joined together. At the same time, the Horn of Africa will likely become an island as the Indian Ocean helps fill in the basins around present day Lake Victoria.
The Pacific pushes back
So if expansions are clearly taking place, what about the question of contraction in the Pacific? One complication is that the Pacific Ocean actually sits on more than one tectonic plate, and they’re not all moving in the same way. The East Pacific Rise is another point of tectonic expansion, stretching from Baja California, under Easter Island, and then past the southern tip of New Zealand. It’s actually adding between six to 16 centimeters of crust per year, suggesting that it’s outgrowing the Mid-Atlantic Ridge. However, some of that is undone by the way other plates are interacting. The Nazca plate, which sits between the East Pacific Rise and the coast of Chile, is actually being consumed thanks to this subductive movement. As the Rise pushes the Nazca towards South America, the plate is being pushed down below the continent, raising the Andes Mountains while otherwise being recycled deeper in the Earth.
Squishing together a new supercontinent
At this point, the trend seems to be that the Pacific Ocean will eventually shrink. Australia will likely end up mashed against southern Asia, and North America will be pushed west towards Asia as well, although in a way that may reopen much of the Pacific Ocean. After 100 million more years, there’s actually a decent chance the world will be home to yet another supercontinent. One prediction for this new landmass has been named Amasia, created from the Americas being mashed into Asia, just as the name implies. This model also predicts the eventual joining of South and North America, leaving the world’s land arranged in a giant crescent shape when viewed from the North Pole. There’s a lot of room for speculation at this point of course, so there’s also a chance we could instead end up with Pangea Proxima or Novopangea instead. Don’t let those last two names mislead you though— Pangea isn’t our only model for a supercontinent, as it certainly wasn’t the first or last time all the continents would be mashed together.
Source: Earth: Our Habitable Planet Chapter 13: Evolution of Continents and Oceans by Dr. Jürgen Schieber, Indiana University