The Pacific Ocean is the largest feature on Earth's surface. It is also, geologically speaking, slowly disappearing.
Scientists say the vast ocean basin is shrinking because of the constant movement of tectonic plates, a process that has been shaping the planet for hundreds of millions of years.
According to the National Oceanic and Atmospheric Administration (NOAA) Ocean Exploration, the Pacific spans more than 155 million square kilometres, covering about a third of Earth's surface and holding roughly half of all the water in the world's oceans. Its area alone exceeds the combined landmass of every continent and island on Earth.
The Pacific formed about 200 to 250 million years ago when the supercontinent Pangaea broke apart and the ancient superocean Panthalassa began to fragment. As the continents drifted, the Atlantic Ocean expanded while Panthalassa gradually evolved into today's Pacific.
Now the process is slowly reversing.
The reason lies beneath the ocean floor. New seafloor forms where tectonic plates pull apart at mid-ocean ridges, allowing molten rock to rise and solidify. Elsewhere, old oceanic crust is destroyed at subduction zones, where one tectonic plate sinks beneath another into Earth's mantle. Whether an ocean grows or shrinks depends on which of these processes dominates.
Around the Pacific, destruction is winning. The ocean is almost surrounded by subduction zones that make up the Ring of Fire, a chain of deep trenches, volcanoes and earthquake-prone regions stretching from New Zealand through Japan to the west coast of the Americas. Although new crust continues to form at the East Pacific Rise, it is being consumed more rapidly along the surrounding trenches, causing the basin to contract over millions of years.
One of these trenches, the Mariana Trench, marks the deepest point on Earth at nearly 11 kilometres below sea level. It is also one of the places where the Pacific plate is slowly sliding back into the planet.
Scientists emphasise that this is an extremely slow geological process.
A 2022 study led by Chuan Huang of Curtin University, published in the journal National Science Review, used supercomputer simulations to model Earth's future. The researchers concluded that the Pacific could close within 200 to 300 million years, eventually bringing Asia and the Americas together to form a new supercontinent they named Amasia. Curtin University summarised the findings following the study's publication.
Other models predict different outcomes, including one in which the Atlantic Ocean closes instead. The exact future remains uncertain.
One point, however, is clear. The water in the Pacific is not disappearing. Only the shape and size of the ocean basin are changing as Earth's tectonic plates continue their slow rearrangement. The process is entirely natural and unrelated to climate change.
For now, the Pacific remains as vast and enduring as ever. Its gradual shrinkage is measurable only on geological timescales, unfolding over hundreds of millions of years.