Resolving the enigmatic Precambrian-Cambrian boundary event (BACE)

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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.