Dating technique

Fossil corals found above or below current sea level show variations in sea level and can be dated by radiocarbon for the past 40,000 years and by the radioactive decay of uranium to thorium for the past 500,000 years.

Unfortunately, corals that appear to be otherwise pristine often have more of the isotopes used for dating than can be explained by radioactive decay, making their ages unreliable.

“Sea level is more variable than previously thought over a period between 70,000 and 250,000 years ago,” said William Thompson, a postdoctoral fellow in the WHOI Geology and Geophysics Department and lead author of the study.

“Substantial shifts occur over a few thousand years, during both glacial and interglacial periods, with rates of change that exceed estimates of modern sea level rise.

Their approach improves sea-level reconstructions using coral ages and indicates that past sea level changes have been too frequent to be explained solely by orbital changes.

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Researchers from the Woods Hole Oceanographic Institution (WHOI) and Columbia University developed a new set of dating equations to determine the ages of corals from the Pacific and Atlantic Oceans to help resolve a longstanding question about the influence of Earth’s orbital variations on sea-level rise in the past.They also compared their data with salinity records from the Red Sea and found similar agreement, further verifying their model.The team’s findings raise questions about the conditions required for the growth of ice sheets and the causes of rapid changes in sea level.Without the ability to date archaeological sites and specific contexts within them, archaeologists would be unable to study cultural change and continuity over time.No wonder, then, that so much effort has been devoted to developing increasingly sophisticated and precise methods for determining when events happened in the past.

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