Collaborative Research: Did the Formation of the Great Unconformity Trigger Oxygenation and the Cambrian Explosion?

大不整合面（GU）代表了岩石记录中最大的时间间隔之一。由于它是紧随其后的寒武纪辐射，生命的生物多样性和复杂性的最显着增加之一，长期以来一直认为这些现象是相互关联的。地球科学家提出，GU是由地壳的大规模侵蚀造成的。随着岩石风化和溶解，一种对生命至关重要的元素磷被释放出来，并被河流带到海洋中。磷的增加被认为刺激了蓝细菌之间的光合作用，从而增加了海洋和大气中的氧含量。这种氧化作用可能是导致寒武纪辐射的导火索，因为复杂的生命需要氧气。尽管GU在生命中最重要的转变之一中发挥着潜在的作用，但人们对它发生的时间和地点知之甚少。确定GU何时形成以及导致其形成的最后一次侵蚀事件的大小对于确定地球历史这一关键时期生命和环境变化的可行机制至关重要。该研究项目利用锆石和钛铁矿（U-Th）/He方法的进展来解释GU的发展。结果直接验证了将大陆侵蚀与氧化和生命爆发联系起来的假设。该项目还通过培训本科生和研究生以及K-12教师来促进对科学和技术的理解。有人提出，大不整合面以下的侵蚀是超大陆分裂、雪球地球冰川作用或全球性的euclide的结果，并可能向海洋输送了生物限制性的营养物质，为寒武纪辐射提供了燃料。然而，大不整合的时间、提出的全球同步性和规模以前没有被测试或限制。（U-Th）/He热年代学的最新进展允许访问所需的热历史解开这个标志性的功能的历史。该项目将获取沿两个不同的南极边缘的沿着两个断面的样品的锆石和钛铁矿（U-Th）/He数据。研究地点将有针对性地充分利用新元古代和寒武纪的地质限制，这将是至关重要的缩小范围的可行的热历史，使GU形成模型之间的歧视。研究结果将极大地改善对新元古代冷却历史的限制，这将被用来测试竞争模型GU的发展和significance.This奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

The Great Unconformity (GU) represents one of the largest gaps of time in the rock record. Since it is followed by the Cambrian Radiation, one of life's most significant increases in biodiversity and complexity, it has long been thought that these phenomena are linked. Geoscientists have proposed that the GU was caused by large-scale erosion of Earth's crust. As rocks weathered and dissolved, an element critical to life, phosphorous, was released and carried to the ocean by rivers. The increase in phosphorous is proposed to have spurred photosynthesis among cyanobacteria, which then increased the oxygen content of the ocean and atmosphere. This oxygenation was perhaps the fuse that led to the Cambrian Radiation since complex life requires oxygen. Despite the GU's potential role in one of life's most important transformations, very little is known about when and where it occurred. Determining when the GU developed and the size of the last erosion event that lead to its formation are critical for identifying viable mechanisms for life and environmental change during this pivotal interval of Earth history. This research project is making use of advances in zircon and titanite (U-Th)/He methods to decipher GU development. Results are directly testing hypotheses that relate continental erosion to oxygenation and the explosion of life. The project is also advancing scientific and technological understanding through the training of undergraduate and graduate students and K-12 teachers. It has been proposed that the erosion below the Great Unconformity occurred as the result of supercontinental breakup, Snowball Earth glaciation, or global eustasy, and may have delivered bio-limiting nutrients to the ocean that fueled the Cambrian Radiation. However, the timing, proposed global synchroneity, and magnitude of the Great Unconformity have not been previously tested or constrained. Recent advances in (U-Th)/He thermochronology allow access to the thermal histories required to unravel the history of this iconic feature. This project will acquire zircon and titanite (U-Th)/He data for samples along two transects across two different cratonic margins. Study sites will be targeted to fully exploit Neoproterozoic and Cambrian geologic constraints, which will be vital for narrowing the range of viable thermal histories to enable discrimination between GU formation models. The results will dramatically improve constraints on the Neoproterozoic cooling history of each margin, which will be used to test competing models for GU development and significance.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.