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Southeast USA

Evidence of tilting of the U.S. coast

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South Africa

Accurate sea level markers

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Roe Plains, Australia

The team’s first expedition

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Researchers take advantage of a celestial collision

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New Zealand

Uplift exposes a repository of Pliocene sediments

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Researchers study crater of hydrogen bomb test

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Artist conception of the meteorite that crashed into the Chesapeake Bay about 34 million years ago, creating the Cheseapeake Bay impact structure. Photo: Nicolle Rager-Fuller, NSF

About 35 million years ago, a meteorite slammed into Earth at the mouth of Chesapeake Bay in Virginia, The impact blasted open a hole about 38 kilometers (24 miles) across and 1.3 kilometers (0.8 miles) deep, a feature researchers call the Chesapeake Bay impact structure. Gradually, the underwater crater filled with sediment, including microscopic, single-celled organisms called foraminifera. A team of scientists at Rutgers University has drilled a 1,766-meter (5,794-foot) -deep hole into the sediment and taken core samples. They’ve used the sediment they’ve collected to estimate sea level during the Pliocene.

Just as the Pliomax team identifies past beaches by finding organisms that live near the coast, the Rutgers researchers use their knowledge of the habitats of various foraminifera species in core samples to estimate how far below sea level the sea bed was when sediment layers were formed. The researchers have dated some of the foraminifera to the Pliocene, using the same strontium method employed by the Pliomax team.

The Rutgers team compares the Pliocene depth of samples with the current depth to calculate sea level change. First, however, they use a process called backstripping to adjust measurements of current depth to take into account forces that have vertically moved the land since sediment layers accumulated millions of years ago. Taking into account these factors, the team estimates that sea level was 10-18 meters (33–59 feet) higher during the Pliocene.