Exploring the Limits of Life on Earth: Environmental Extremes of the Neoproterozoic 'Super' Glacial and Interglacial Cycles

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AbstractThe geoloica1 record of the Neoproterozoic Era (1,000-543 Ma) indicates that Earth's climate alternated between warm equable conditions anti severe glacial conditions in which continental-scale ice sheets extended at sea level equatorward of 20 latitude. Macroscopic multicellular organisms make their first unequivocal appearance in the fossil record just prior to the Varanger glacial interval (600-575 Ma). Researchers have speculated that the extreme climatic conditions of tile Varanger glaciation may have acted as a catalyst for the rapid evolution of more complex metaoans such as the Ediacara fauna in the latest Neoproterozoic. For this to be so, however, the ancestral metazoans first had to endure what was quite probably the harshest global climate to have existed since the beginning of Earth history. and then had to survive an equally harsh phase of rapid global warming. This project seeks to better quantify the range of paleoclimatic conditions through which the early metazoans survived from the height of the Varanger glaciation to the warm, post-glacial conditions. What combination of climate forcingfactors and feedbacks can best reproduce the extreme glacial conditions, and yet provide a means of returning to a warmer, more equable climate? What were Earth surface conditions like in terms of temperature and aridity?The project will employ existing geological data to create improved reconstructions of Neoproterozoic paleogeography. Thc reconstruction will then be used as boundary conditions for a series of climate model simulations using a state-of- thc-art global climate model (GCM). Building upon our body of previous simulations, which used an older, coarse-resolution GCM. we have designed a sequence of experiments that will examine the Neoprotenozoic extreme cold phases, extreme warm phases, and transitional phases from one state to the other. The new simulations add realism and accuracy that will allow for a better description of regional climate conditions and help us delimit the range of forcings and feedback processes that operated during this pivotal period in Earth history. Rigorous and quantitative examination of the results will provide detailed new information about how such a severe climatic deterioration could have occurred here on Earth, and how the climate system recovered to more equable state. This project should yield valuable insights into the long-term ability of Earth life forms to adapt to extreme environmental conditions, and will expand our view of other planetary environments that may have supported, or be capable of supporting, Earth-like life.