This pilot project will attempt obtain precise radiometric ages from critical levels to of an Ocean Drilling Program drill core (site 758). Feldspar mineral grains will be separated from 18 different volcanic tephra layers and then subjected to analysis using the laser 40Ar/39Ar dating technique. This method has unprecedented sensitivity and precision, and if suitable material can be extracted from these volcanic horizons, ages with accuracies to within a few thousand years can be obtained. Since this core been studied using oxygen isotopic and paleomagnetic methods, the time-scale derived could precisely calibrate the entire magnetic and global climate change chronology over the past 5 million years. Divergences between the theoretically expected periodicities of oxygen isotope ratio variations and the standard magnetic reversal time scale have raised serious questions about its accuracy. Laser 40Ar/39Ar dating has probably the greatest potential for resolving these questions. However, the project is 'high-risk' in the sense that is not yet known if sufficient datable material can be obtained from ODP cores. If successful, this project could not only improve the currently accepted time scale of global climatic change, it also has the potential for being able to estimate the response rate of the earth to the now well-established astronomical inputs to the earth's climate system.
