for National Geographic News
A new analysis of deep sediment cores taken from the New Jersey coast has revealed unexpected ice in the otherwise warm dinosaur-ruled world 50 to 100 million years ago.
Data from the cores also show dramatically lower sea levels for the period than previously thought. Finally, the study suggests that the rate of sea-level rise has doubled during the last 150 years.
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The new report, published in the November 25 issue of the journal Science, spans the past 540 million years and is based largely on studies of 11 core samples each 1,600 feet (500 meters) long.
The greatest difficulty in establishing long-term sea level changes has been the complexity of removing outside influences from the calculations, according to lead author Ken Miller.
Miller, a geologist at Rutgers University in Piscataway, New Jersey, says events such as the rise and fall of continental landmasses can affect the data.
"There's no place that's completely stable," Miller said. But New Jersey's instabilities during the past billion years have been fairly predictable, so they can be filtered out reliably using ever-improving methods.
This makes cores from the area one of the best available records of long-term sea level change, he said.
The researchers dated sections of the cores using common radiological methods and other techniques. They then analyzed the samples in a variety of ways to determine sea level at a specific period.
For example, the type of material, such as sand or finer marsh sediment, found at a particular depth was used to determine the sample location's proximity to the ocean.
If the location was submerged at a particular time, sea-life fossils could indicate how deep the water was, because certain animals are found only at specific depths.
One of the study's most striking finds was that ice existed during a period of time geologists had been convinced was ice-free.
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