SGER: Search for Earliest Metazoans

SGER：寻找最早的后生动物

• 批准号: 0902554
• 负责人: L. Paul Knauth
• 金额: $ 2.13万
• 依托单位: Arizona State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-03-01 至 2011-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0902554&HistoricalAwards=false
• 关键词: SGER; Search; Earliest; Metazoans

Search for Earliest MetazoansL Paul KnauthArizona State UniversityNewly discovered latest Precambrian pond sediments deposited in Western Australia Precambrian will be explored for body fossils and trace fossils of metazoans that may have existed prior to the Cambrian explosion of life in the sea. Controversial molecular clock results suggest that metazoans evolved in the Late Precambrian, but exhaustive searches of Precambrian marine sedimentary rocks have not yielded evidence of abundant and diversified metazoans. Dissolved oxygen may have been too low in the seas until salinity was lowered by deposition of enormous salt deposits in the late Precambrian. The possibility arises that metazoans were extensively evolved as soft-bodied organisms in lower salinity non-marine environments and moved subsequently into the sea to create the species diversity characteristic of the Cambrian Explosion. Lake sediments are rapidly eroded off continents, and no previous late Precambrian examples are known to test these ideas. The Australian pond sediments were discovered during field work for other purposes and have not been mapped or studied. They fill isolated depressions on an ancient solution surface (paleokarst) developed on the Proterozoic Eliot Range Dolomite. They are immediately overlain by non-marine sands and latest Precambrian glacial tillite. They include cycles of laminated carbonate interbedded with shales. The carbonates contain replacement chert and insoluble residues of phosphatic material known to preserve even the smallest metazoan fossils in younger strata. The SGER grant will support field work to identify and map the best pond deposits, search for trace fossils, and obtain an extensive collection of the freshest material for thin sections and subsequent SEM and microscopic examination of insoluble residues. Stanley Awramik (University of California, Santa Barbara) and ASU student Hope Johnston will participate in the field work and lab investigations. Evidence of metazoans in these rocks would indicate that the great metazoan expansion of life was a result of previously evolved lineages moving into the sea rather than some environmental or biological change that allowed them to originate in the sea in a very short interval of time. Current efforts to understand what possible environmental or biological changes allowed an explosion of life would transform to a new effort to understand the antiquity and evolution of life in the non-marine environments which are so infrequently preserved in the geologic record.

寻找最早的后生动物L Paul Knauth亚利桑那州立大学新发现的沉积在西澳大利亚前寒武纪的最新前寒武纪池塘沉积物中，将探索前寒武纪可能存在于寒武纪海洋生命爆发之前的后生动物的身体化石和痕迹化石。 有争议的分子钟结果表明，后生动物在前寒武纪晚期演化，但对前寒武纪海洋沉积岩的详尽研究并未得出后生动物丰富且多样化的证据。 海洋中的溶解氧可能太低，直到前寒武纪晚期大量盐沉积物的沉积降低了盐度。 后生动物有可能在盐度较低的非海洋环境中广泛进化为软体生物，随后进入海洋，形成寒武纪大爆发的物种多样性特征。湖泊沉积物迅速从大陆上被侵蚀，并且之前没有已知的前寒武纪晚期的例子来检验这些想法。 澳大利亚池塘沉积物是在出于其他目的的实地工作中发现的，尚未绘制或研究。 它们填充了元古代艾略特山脉白云岩上形成的古老溶液表面（古岩溶）上的孤立凹陷。它们立即被非海洋沙子和最新的前寒武纪冰川冰屑覆盖。 它们包括与页岩互层的层状碳酸盐循环。 碳酸盐含有替代燧石和磷酸盐物质的不溶性残留物，已知这些物质甚至可以保存较年轻地层中最小的后生动物化石。 SGER 赠款将支持实地工作，以确定和绘制最佳池塘沉积物的地图，寻找痕迹化石，并获取大量最新鲜的材料用于薄片以及随后的扫描电镜和不溶性残留物的显微镜检查。 Stanley Awramik（加州大学圣塔芭芭拉分校）和亚利桑那州立大学学生 Hope Johnston 将参加现场工作和实验室调查。 这些岩石中存在后生动物的证据表明，后生动物生命的巨大扩张是先前进化的谱系移入海洋的结果，而不是某些环境或生物变化使它们在很短的时间内起源于海洋。 当前了解哪些可能的环境或生物变化导致生命爆发的努力将转变为了解非海洋环境中生命的古代和进化的新努力，而这些环境很少保存在地质记录中。