Resolving the enigmatic Precambrian-Cambrian boundary event (BACE)

查尔斯达尔文的“大难题”是，为什么以动物化石形式存在的复杂生命似乎在大约5.4亿年前（Ma）的岩石中突然出现，这就是众所周知的寒武纪大爆发。虽然我们现在知道，许多化石是在稍微古老的岩石中发现的，但寒武纪大爆发的触发器和驱动器仍然非常神秘。这一革命性的事件发生在碳同位素揭示的碳循环扰动之后。这被称为寒武纪碳同位素漂移（BACE），尽管人们早就知道，但这一事件仍然非常神秘。这是因为没有一个单一的地层剖面可以让我们创建一个完整的图像，这需要包括关键化石的发现地点和时间，可以告诉我们地球环境在这个时候如何变化的地球化学，最后是岩石的绝对年龄（日期），以便我们可以重建事件的确切顺序。这意味着我们对这一深刻的进化转变的理解仍然非常不确定。在这个项目中，我们将使用来自地下钻探岩心的独特和新的沉积岩档案。这使我们能够构建一个更高分辨率的，四维（时空）的最早的动物和他们的环境的进化历史的图片。这些岩心来自三个不同的地方：纳米比亚、巴西和中国南方，因此我们可以将当地模式与全球模式进行比较。这样的岩心是未风化的，因此将尽可能保留最准确的地球化学特征。我们还组建了一个非常多学科的团队，该团队结合了以下方面的互补专业知识：1）地质年代学-岩石测年; 2）地球化学-重建营养和地球化学循环; 3）古生物学-生命和进化的记录;以及4）数学建模，这将使我们能够捕获地质信息，以这种方式来测试关于动物进化对环境稳定性的影响的关键假设。我们的项目旨在解决三个核心科学问题：问题1：BACE是局部的还是全球的，成岩的还是原生的？Q2：BACE的原因是什么？问题3：BACE在后生动物的进化中扮演了什么角色？我们将考虑环境因素，如氧气水平的变化，作为进化变化的驱动力。通过区分物理的、外在的驱动因素，我们可以解决一个基本的、激励性的问题：是什么导致了动物的进化和辐射？这个独特的数据集可能是变革性的，因为它将解决地球系统耦合进化和复杂生命兴起的关键过程。这项研究与今天的生物圈有关，因为现代地球系统及其稳定反馈就是在这个关键时期出现的。通过更详细地研究它，并建立关键事件之间的时间关系和因果关系，我们可以发现现代地球系统及其所携带的独特生命是如何构建的。

Charles Darwin's 'great dilemma' was why complex life in the form of fossil animals seemed to appear so abruptly in rocks around 540 million years ago (Ma), in what is widely known as the Cambrian Explosion. Although we now know that many fossils are found in slightly older rocks, nonetheless the triggers and drivers of the Cambrian Explosion remain highly enigmatic. This revolutionary event follows immediately after a perturbation in the carbon cycle as revealed by carbon isotopes. This is known as the BAsal Cambrian carbon isotope Excursion (the BACE), and although has long been known, this event remains highly enigmatic. This is because there is no single stratigraphic section that allows us to create an integrated picture, which needs to include where and at what time the key fossils are found, the geochemistry that can tell us about how the Earth's environment may have changed at this time, and finally absolute ages (dates) of the rocks so that we can reconstruct the exact order of events. This means that our understanding of this profound evolutionary transition remains very uncertain.In this project we will use unique and new archives of sedimentary rocks derived from drilled, subsurface cores. This enables us to construct a much higher resolution, four-dimensional (temporal-spatial) picture of the evolutionary history of the earliest animals and their environment. These cores are from three diverse locations: Namibia, Brazil and South China, so that we can compare local to global patterns. Such cores are unweathered, so will preserve the most accurate geochemical signatures possible. We have also assembled a very multidisciplinary team, which combines complementary expertise in: 1) geochronology - the dating of rocks; 2) geochemistry - for reconstructing nutrient and biogeochemical cycles; 3) palaeontology - the record of life and evolution; and 4) mathematical modelling, which will enable us to capture geological information, in such a way as to test key hypotheses about the effects of animal evolution on environmental stability. Our project aims to address three central scientific questions: Q1: Is the BACE local or global, diagenetic or primary? Q2: What were the causes of the BACE? and Q3: What role did the BACE play in the evolution of metazoans? We will consider environmental factors, such as changes in oxygen levels, as the drivers of evolutionary change. By distinguishing physical, extrinsic drivers we can address a fundamental and motivating question: what caused animals to evolve and radiate when they did? This unique dataset is likely to be transformative as it will resolve the key processes fundamental to the coupled evolution of the Earth System and the rise of complex life.This study has relevance to today's biosphere, as the modern Earth system and its stabilising feedbacks arose during this key interval. By studying it in more detail, and establishing temporal relationships and causality between key events, we can find out how the modern Earth system and the unique life it carries, is structured.