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April 15, 2005 Corals from Papua New Guinea and Barbados indicate that changes in sea level, one of the key indexes for global climate change, may have been more frequent in the past than previously thought, according to a report in today’s issue of Science.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.We refer to this new dating approach as ‘open-system’ dating.” Thompson and Goldstein compared speleothem records of sea level and climate from caves in the Austrian Alps, France, Tasmania and Brazil with their sea-level reconstructions for corals.They found agreement for high sea level at times of warm, wet climate conditions and lower sea level at times of cold/drier climate conditions.These techniques are based upon the measurement of radioactive processes (radiocarbon; potassium-argon, uranium-lead, uranium-thorium, thorium-lead, etc.; fission track; thermoluminescence; optically stimulated luminescence; and electron-spin resonance), chemical processes (amino-acid racemization and obsidian hydration), and the magnetic properties of igneous material, baked clay, and sedimentary deposits (paleomagnetism).Other techniques are occasionally useful, for example, historical or iconographic references to datable astronomical events such as solar eclipses (archaeoastronomy).

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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.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.Reef corals are commonly used to reconstruct changes in sea level over time because they grow near the sea surface.In archaeology, dating techniques fall into two broad categories: chronometric (sometimes called “absolute”) and relative.Chronometric dating techniques produce a specific chronological date or date range for some event in the past. Relative dating techniques, on the other hand, provide only the relative order in which events took place.

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