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

寒武纪(5.39-4.85亿年前)的岩石中含有化石，揭示了地球上第一批动物的多样性。人们对这场寒武纪大爆炸的时间、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，这些地层是在海洋淹没世界大陆时形成的，沿海环境覆盖着大片沙子、泥土和化石。保存最完好的这些事件的记录之一是在大峡谷的底部--在被称为托托群的一组沉积岩中。尽管托托集团已经被研究了近150年，但新技术的出现使我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，并导致对地球上寒武纪生命爆发的更多了解。这项研究的更广泛影响包括指导一批博士后、研究生和本科生，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年轻受众，包括农村、第一代、第一民族、市中心和文化多元化环境中的4-12年级学生。最后，这个项目将通过公园项目、展品、媒体和NSF赞助的大峡谷地质实地论坛，接触到大峡谷国家公园每年600万游客中的许多人。寒武纪岩石记录了地球系统的戏剧性变化，包括大气氧化事件，碳循环的大范围扰动，以及动物生命的断断续续的进化。这些事件是在全球大陆海侵期间发生的，它们推进了沉积了片状沙子、泥浆和碳酸盐的海洋。支撑这项研究计划的是一种新颖的综合方法，以校准这次海洋入侵的时间和节奏。这种方法结合了：a)隐藏在构成这些沉积岩的碎屑中的最年轻的准同期沉积的锆石晶体的放射性同位素测年；b)确定同一岩石中化石类型的变化；以及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--例如海平面的变化或大陆的碰撞和解体。初步研究表明，大峡谷的托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，并在整个美国西部增加同期地层，以测试关于这些洪水事件如何与全球生物、构造和地球物理事件和过程相关的假设。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.