Earth’s Mantle Affects Sea Level Rise Estimates
A prehistoric shoreline runs along the eastern edge of North America; scientists have pointed to it as evidence that much of Antarctica melted 3 million years ago. But new research suggests this shoreline is actually about 30 feet (10 meters) lower than previously thought, meaning less ice melted than suspected.
The shoreline, which should be flat, also swoops up and down the East Coast like a set of wave crests, reflecting tugging and pushing by Earth’s mantle, the layer of viscous rock leisurely oozing underneath the crust, according to the study, published today (May 16) in the journal Science Express.
The finding shows that scientists have to be careful when looking at Earth for evidence of past sea level changes from the planet’s cycles of glacial advance and retreat.
"You simply can’t go somewhere and look at the height of the shoreline and infer anything about the amount of water in the oceans or the height of sea level without already knowing an awful lot about what the mantle is doing," said David Rowley, lead study author and a geologist at the University of Chicago.
The East Coast shoreline as it appeared 3 million years ago. The shoreline has been adjusted 82 feet (25 meters) relative to today.
This interplay between the surface elevation of the Earth and the mantle is called dynamic topography. The cliffs of the Great Australian Bight and the tall height of the African continent are also attributed to the mantle’s effects on topography. Even the Appalachian Mountains may owe their enduring height to the mantle.
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