Collaborative Research: Constraining the tempo and dynamics of Cambrian Earth systems in western Laurentia

寒武纪（5.39 - 4.85亿年前）的岩石中包含的化石揭示了地球上动物的第一次多样化。人们对这次“寒武纪大爆发”的时间、原因和影响知之甚少。然而，了解这一事件的线索埋藏在寒武纪地层中，寒武纪地层是海洋淹没世界大陆时形成的，沿海环境用大片的沙子、泥土和化石覆盖了这一景观。这些事件保存最完好的记录之一是在大峡谷的底部，在一组被称为通托群的沉积岩中。尽管人们对托托群的研究已经有近150年的历史，但新技术的出现使人们有时间重新审视这些经典的曝光。这个项目将破译这些岩石是如何、何时以及为什么沉积的，并使我们对地球上寒武纪生命大爆发有更深入的了解。这项研究的广泛影响包括指导一系列博士后、研究生和本科生学者，包括招募和培训西班牙裔和美洲原住民学生。影响还包括通过丹佛自然与科学博物馆进行外展和远程学习，以帮助这项研究激励更年轻的受众，包括农村、第一代、第一民族、市中心和文化多样化环境中的4至12年级学生。最后，这个项目将通过公园项目、展览、媒体和美国国家科学基金会赞助的大峡谷地质实地论坛，向每年600万游客中的许多人宣传。寒武纪岩石记录了地球系统的巨大变化，包括大气氧化事件、碳循环的大范围扰动和动物生命的间断进化。这些事件是在全球海侵淹没大陆的过程中发生的，海洋的推进沉积了薄砂、泥和碳酸盐。支撑研究计划的是一种新颖的、综合的方法来校准这种海洋海侵的时间和速度。这种方法结合了：a)对最年轻的、准同时期沉积的锆石晶体进行放射性同位素定年，这些锆石晶体隐藏在构成这些沉积岩的碎屑中；B)识别同一岩石中化石类型的变化；c)记录这些岩石的矿物、化学和物理特征的变化，这些变化记录了寒武纪地球系统中同时发生的相关变化，如海平面的变化或大陆的碰撞和分裂。最初的研究表明，大峡谷的通托群比之前认为的要年轻数千万年，海洋淹没北美的速度相对较快，其他大陆边缘也经历了同样的事件。该项目将扩展在大峡谷进行的一项试点研究，并将其扩展到美国西部的同时期地层，以测试这些洪水事件与全球生物、构造和地球物理事件和过程之间的关系。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Rocks from the Cambrian Period (539-485 million years ago) contain fossils that reveal the first diversification of animals on Earth. The timing, causes, and impacts of this “Cambrian Explosion” are poorly understood. Yet clues to understanding this event are buried in Cambrian strata that formed as oceans flooded the world’s continents, and coastal environments blanketed the landscape with vast swaths of sand, mud, and fossils. One of the best-preserved records of these events is in the bottom of the Grand Canyon—in a package of sedimentary rocks known as the Tonto Group. Although the Tonto Group has been studied for nearly 150 years, the availability of new techniques makes it time to revisit these classic exposures. This project will decipher how, when, and why these rocks were deposited, and lead to greater understanding of the Cambrian Explosion of life on Earth. The broader impacts of this research include mentoring a suite of post-doctoral, graduate, and undergraduate scholars, including recruiting and training Hispanic and Native American students. Impacts also include outreach and distance learning through the Denver Museum of Nature and Science, to help this research inspire younger audiences, including 4th-12th graders in rural, first-generation, first-nation, inner-city, and culturally diverse settings. Finally, this project will reach many of the six million annual visitors to Grand Canyon National Park through Park programs, exhibits, media, and NSF-sponsored field forums on Grand Canyon geology. Cambrian rocks record dramatic changes in Earth systems including atmospheric oxygenation events, large magnitude perturbations to the carbon cycle, and the punctuated evolution of animal life. These events played out within the global transgressive inundation of continents by advancing oceans that deposited sheet sands, muds, and carbonates. Underpinning the research plan is a novel, integrative approach to calibrating the timing and tempo of this marine transgression. This approach combines: a) radioisotopic dating of the youngest, penecontemporaneously deposited zircon crystals, which are hidden amidst the detritus making up these sedimentary rocks; b) identifying changes in the types of fossils in the same rocks, and; c) documenting changes in mineral, chemical, and physical signatures of these rocks that record simultaneous, related changes in the Cambrian Earth system—such as changes in sea level or the collision and breakup of continents. Initial work has shown that the Tonto Group of the Grand Canyon is tens of millions of years younger than previously thought, that seas flooded North America relatively quickly, and that other continental margins experienced the same event. The project will expand upon a pilot study that was conducted in the Grand Canyon, and augment it with contemporaneous strata throughout the western U.S. to test hypotheses about how these flooding episodes relate to global biologic, tectonic, and geophysical events and processes.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.