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

摘要新元古代（1000 -543 Ma）的地质记录表明，地球气候在温暖的均等化条件和严重的冰期条件之间交替，冰期条件下大陆尺度冰盖在海平面向赤道20纬度延伸。宏观多细胞生物在瓦朗热冰期（600-575 Ma）之前的化石记录中首次明确出现。研究人员推测瓦朗格冰期的极端气候条件可能是更复杂的动物快速进化的催化剂，比如新元古代晚期的埃迪卡拉动物群。然而，要做到这一点，后生动物祖先首先必须忍受可能是自地球历史开始以来最严酷的全球气候。然后还要在同样严酷的快速全球变暖阶段生存下来。该项目旨在更好地量化早期后生动物从瓦朗格冰期高峰到温暖的后冰期生存的古气候条件的范围。什么样的气候强迫因子和反馈的组合能最好地重现极端的冰川条件，并提供一种回归到更温暖、更均匀的气候的方法？地球表面的温度和干旱程度是怎样的？该项目将利用现有的地质数据对新元古代古地理进行改进重建。然后，利用最先进的全球气候模式（GCM），将Thc重建用作一系列气候模式模拟的边界条件。建立在我们之前的模拟的基础上，这些模拟使用的是旧的、粗分辨率的GCM。我们设计了一系列实验来研究新元古代的极冷阶段、极暖阶段和从一种状态到另一种状态的过渡阶段。新的模拟增加了真实感和准确性，将允许更好地描述区域气候条件，并帮助我们划定在地球历史上这一关键时期运作的强迫和反馈过程的范围。对结果进行严格和定量的检查将提供详细的新信息，说明如此严重的气候恶化是如何在地球上发生的，以及气候系统如何恢复到更平衡的状态。这个项目将对地球生命形式适应极端环境条件的长期能力产生有价值的见解，并将扩大我们对其他可能支持或有能力支持类地生命的行星环境的看法。

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.