The Origin and Expansion of Silica Biomineralization and Its Influence on the Global Silica Cycle

一些海洋生物的骨骼是由蛋白石二氧化硅构成的。在现代海洋中，这一过程--二氧化硅生物矿化--在调节地球气候和主要元素循环方面发挥着重要作用。对岩石记录的观察提供了相互矛盾的观点，即第一批二氧化硅生物矿化剂是在多长时间前进化出来的，以及它们在调节海洋方面是否像它们的现代亲属一样发挥着重要作用。这个项目将通过测量最古老的海绵和放射虫化石中硅的稳定同位素组成来研究这些问题，重点是来自美国西部的样品，年龄从5.2亿到4.4亿年不等。该项目将包括研究生、本科生和高中生的研究培训；200名小学女孩的科学参与体验；以及开发关于第一种二氧化硅生物矿化剂的博物馆展览。古生代初期硅质生物矿化作用的演化和扩展，开启了硅质旋回的转变，从严格的非生物反应控制的系统向现代海洋的生物主宰的旋回转变。我们目前对这种转变的理解受到关于第一批二氧化硅生物矿化剂进化和扩张时间的相互矛盾的数据的限制，以及关于它们对二氧化硅循环的影响的未经检验的假设。该项目将通过解决两个主要研究目标来弥合这一知识鸿沟：(1)记录化石海绵针状体和放射虫的保存模式，以评估它们对保存原始硅同位素价值的影响；(2)改进寒武纪-奥陶纪对化石海绵针状体和放射虫中硅同位素价值的记录。这项工作将包括通过二次离子质谱仪现场分析硅质化石的硅和氧同位素比值，结合通过显微X射线荧光、拉曼显微光谱和波长色散X射线光谱进行额外的微观分析表征，以及一套描述海洋硅循环的模型。这些数据将提供一种新的方法来解决围绕全球硅质循环早古生代生物转化的长期存在的问题，包括海洋系统如何应对气候和构造驱动的硅酸盐风化通量的主要扰动。这一奖项反映了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。

Some marine organisms construct their skeletons from opaline silica. In modern oceans, this process—silica biomineralization—plays an important role in the regulation of Earth’s climate and major elemental cycles. Observations from the rock record offer conflicting views on how long ago the first silica biomineralizers evolved and whether they played as important a role in regulating the oceans as their modern relatives. This project will investigate these questions by measuring the stable isotope composition of silicon in the oldest fossils of sponges and radiolarians, focusing on samples from the western US ranging in age from 520-440 million years. This project will include research training for graduate, undergraduate, and high school students; science engagement experiences for 200 elementary school girls; and the development of a museum exhibit on the first silica biomineralizers. The evolution and expansion of silica biomineralization at the beginning of the Paleozoic Era initiated the transformation of the silica cycle from a system governed by strictly abiotic reactions to the biologically-dominated cycle that characterizes modern oceans. Our current understanding of this transition is limited by conflicting data on the timing of the evolution and expansion of the first silica biomineralizers and untested hypotheses about their influence on the silica cycle. This project will bridge this knowledge gap by address two primary research objectives: (1) document the preservational modes of fossil sponge spicules and radiolarians to evaluate their influence on preservation of primary Si isotope values; and (2) build an improved Cambrian-Ordovician record of Si isotope values in fossil sponge spicules and radiolarians. This work will include Si and O isotope ratio analyses of siliceous fossils in situ via secondary ion mass spectrometry, combined with additional microanalytical characterization via micro X-ray fluorescence, Raman microspectroscopy, and wavelength-dispersive X-ray spectroscopy, and a suite of models describing the marine silica cycle. These data will provide a novel approach to resolving long-standing questions surrounding the early Paleozoic biological transformation of the global silica cycle, including how the marine system responded to major perturbations in silicate weathering fluxes driven by climate and tectonics.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.