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Water from the ocean has been steadily draining away into the interior of our planet over the last 230 million years. The loss of water is equivalent to a fall in sea level of at least 50 metres and possibly 130 metres.

The drainage will not affect the current rise in sea levels, which is driven by climate change and ultimately our greenhouse gas emissions. The current rise is taking place over centuries, whereas the natural drainage is 10,000 times slower.

Many processes have , from warmer climates that melt ice sheets, to seafloor rocks becoming denser with age and sinking 鈥� causing sea levels to fall. However, found another significant mechanism: subduction. When one continental plate moves under another and is dragged down into the mantle below, it takes water trapped inside the rock with it.

To find out how much water is lost this way, Krister Karlsen of the University of Oslo in Norway and his colleagues conducted their own study. They built a mathematical model that estimates the flows of water in and out of the Earth鈥檚 interior over the last 230 million years. They found that the key factor is the speed of subduction. The rate increased dramatically around 150 million years ago.

Before then, all the continents were linked together in a supercontinent called Pangaea. But by 150 million years ago Pangaea was disintegrating. 鈥淵ou have much more rapid subduction when you break up a supercontinent,鈥� says Karlsen. 鈥淭he rapid subduction is crucial for bringing water in hydrated rock deep into the mantle.鈥� If the subduction is slow, water in the sinking rocks can escape back up into the sea.

If no other processes were taking place, sea levels would have fallen 50-130 metres in the last 230 million years, with the fastest drops around 150 million years ago. In reality, other processes like sea floors sinking were also going on, so the effect of this drainage was masked.

If the oceans carry on draining at a similar rate, they will be empty in about 12 billion years. However, the Sun is expected to swell into a red giant and destroy the Earth in about 5 billion years, so there鈥檚 no need to worry about it.