Resolving the enigmatic Precambrian-Cambrian boundary event (BACE)

查尔斯·达尔文的“大难题”是，为什么在5.4亿年前，即众所周知的寒武纪大爆发期间，以动物化石形式出现的复杂生命似乎突然出现在岩石中。尽管我们现在知道许多化石是在稍古老的岩石中发现的，但寒武纪大爆发的触发和驱动因素仍然是一个谜。这一革命性的事件紧随碳同位素所揭示的碳循环扰动之后。这被称为基底寒武纪碳同位素偏移（BACE），尽管人们早就知道，但这一事件仍然是高度神秘的。这是因为没有一个单一的地层剖面可以让我们创造一个完整的画面，这需要包括在什么地方和什么时候发现关键化石，地球化学可以告诉我们地球环境在这个时候是如何变化的，最后是岩石的绝对年龄（日期），这样我们就可以重建事件的确切顺序。这意味着我们对这种深刻的进化转变的理解仍然非常不确定。在这个项目中，我们将使用从钻取的地下岩心中提取的独特和新的沉积岩档案。这使我们能够构建一个分辨率更高的四维（时空）图像，描绘最早的动物及其环境的进化史。这些核心来自三个不同的地方：纳米比亚、巴西和中国南方，这样我们就可以将当地的模式与全球的模式进行比较。这样的岩心是未风化的，因此将尽可能保留最精确的地球化学特征。我们还组建了一个非常多学科的团队，其中包括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-用于重建营养和生物地球化学循环；3)古生物学——记录生命和进化；4)数学建模，这将使我们能够获取地质信息，从而检验关于动物进化对环境稳定性影响的关键假设。我们的项目旨在解决三个核心科学问题：Q1: BACE是地方性的还是全球性的，是成岩性的还是原发性的？Q2: BACE的原因是什么？Q3: BACE在后生动物的进化中发挥了什么作用？我们将考虑环境因素，如氧含量的变化，作为进化变化的驱动因素。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、激励人心的问题：是什么导致了动物的进化和辐射？这个独特的数据集可能具有变革性，因为它将解决地球系统耦合进化和复杂生命兴起的关键基本过程。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是在这个关键时期出现的。通过更详细地研究它，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和它所承载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.