International Geologiical Congress - Oslo 2008


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HPS-11 The EARTHTIME project


Solving Earth history problems with the Astronomical Time Scale


Linda Hinnov, Johns Hopkins University (United States)
James Ogg, Purdue University (United States)


The Astronomical Time Scale (ATS) is an important emerging alternative to radioisotope-based geochronology for the past 250 Ma. Quasi-periodic oscillations in the Earth's orbit and axial tilt have been a major driving factor in past climate variations, and have left their record in the climate-sensitive sedimentary record. Extended sequences of these sedimentary oscillations have been calibrated to high-precision astronomical models that have been calculated back in time in years from 1 January 2000 for hundreds of millions of years. These calibrated cyclic sequences constitute the ATS. The ATS has a resolving power that is directly related to the accuracy of the astronomical modeling, and slowly declines from an impressive 0.02-0.04 myr (precession to obliquity scale) in the Neogene, to 0.1 myr (short orbital eccentricity scale) in the Paleogene, to 0.4 myr (long orbital eccentricity scale) in the Mesozoic. This resolving power offers orders of magnitude improvement over that of the current Geologic Time Scale (GTS). The stratigraphic continuity of the ATS helps to maintain high precision in the GTS between ash beds that have been dated by modern geochronology. These collective innovations significantly broaden the problems that can be addressed in Earth history research. Notable examples will be presented that include: (1) high-resolution terrestrial-marine correlation; (2) seafloor spreading rates; (3) source rock formation rates; (4) origin of global marine sequences; (5) occurrence of Cretaceous Oceanic Anoxic Events; (6) pacing of biotic extinction; and (7) prediction of Earth's future climate.


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