PHANEROZOIC PALEOTEMPERATURES: THE EARTH’S CHANGING CLIMATE DURING THE LAST 540 MILLION YEARS

This study provides a comprehensive and quantitative estimate of how global temperatures have changed during the last 540 million years. It combines paleotemperatures measurements determined from oxygen isotopes with broader insights obtained from the changing distribution of lithologic indicators of climate, such as of coals, evaporites, calcretes, reefs, and bauxite deposits. The waxing and waning of the Earth’s great polar icecaps have been mapped using the past distribution of tillites, dropstones, and glendonites. The global temperature model presented here includes estimates of average global temperature (GAT), changing tropical temperatures (∆T˚ tropical), deep ocean temperatures, and polar temperatures. Though similar, in most respects, to the temperature history deduced directly from the study of oxygen isotopes, our model does not predict the extreme high temperatures for the Early Paleozoic required by isotopic investigations. The history of global changes in temperature during the Phanerozoic has been summarized in a “paleotemperature timescale” that subdivides the many past climatic events into 8 major climate modes; each climate mode is made up of 3-4 pairs of warming and cooling episodes (chronotemps). A detailed narrative describes how these past temperature events have been affected by geological processes such as the eruption of Large Igneous Provinces (LIPS) (warming) and bolide impacts (cooling). The paleotemperature model presented here allows for a deeper understanding of the interconnected geologic, tectonic, paleoclimatic, paleoceanographic, and evolutionary events that have shaped our planet. The quantitative paleotemperature model presented here makes explicit predictions about the Earth’s past temperature that can be tested and evaluated. By quantitatively describing the pattern of paleotemperature change through time, we may be able to gain important insights into the history of the Earth System and the fundamental causes of climate change on geological timescales. These insights can help us better understand the problems and challenges that we face as a result of Future Global Warming.