Sea Levels to Plunge Long Term, Study of Dino Era Says

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But it's hard to know exactly what Earth's landmasses might look like in 80 million years, because in addition to sea level changes, plate tectonics should significantly shift the continents.

Some plates will bump and grind, others will drift apart, and still others will dive under landmasses and melt within Earth's hot interior.

According to the new study, a key factor in sea level change is the creation and spreading of new ocean crust along underwater mountain chains called mid-ocean ridges, Müller said.

"As the ocean floor moves away from the hot and shallow mid-ocean ridges into parts of the abyssal plains, it cools and sinks," he explained.

Currently the mid-ocean ridges lie, on average, 1.6 miles (2.5 kilometers) beneath sea level, while the abyssal plains sit 3.7 miles (6 kilometers) deep.

"That's a huge difference, and if you change the relative proportion of mid-ocean ridges and abyssal plains in the ocean basins, you change [the ocean's] volume, and this is what we have tried to reconstruct," he said.

The team found that, during the late Cretaceous, huge mid-ocean ridges wrapped around the planet, making the global ocean much shallower on average than it is today.

In particular, a mid-ocean ridge system in an ancient ocean called Panthalassa—the precursor to the Pacific—was a crucial force driving sea level change through time, Müller said.

Much of that system no longer exists, which largely explains why sea levels have fallen over the last 80 million years.

Going forward, the researchers' model suggests the Atlantic Ocean will continue to grow and the Pacific Ocean will shrink as more mid-ocean ridges disappear.

"As time goes by, we will therefore increase the volume of the ocean basins because it will become deeper than average, so this will result in a long-term sea level drop," Müller said.

Commendable Job

Kenneth Miller is a geologist at Rutgers University in New Jersey.

He has also worked on late Cretaceous sea level estimates, and he commended Müller and colleagues' work.

"In ten years this is still going to be the most widely cited paper on this topic," he said, adding that the latest estimate for Cretaceous-era sea level is more reasonable than any other in the published literature, including his own.

According to Miller, studies like this are important to gain an understanding and appreciation of how plate tectonics drive sea level changes over million-year time scales.

But Miller cautioned against comparing the long-term, plate tectonic-driven changes in sea level to the short-term dangers from melting ice caps.

"The main effect for people who care about what's happening into the future is to understand how fast the ice caps are melting," he said.

And many studies have shown that the ice caps are melting rapidly, pushing sea levels higher.

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