Resolving the enigmatic Precambrian-Cambrian boundary event (BACE)

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.

The main beneficiary from this research will be the general public. More specifically, our targets are: (1) school students, particularly Scottish Higher/A-level and just pre-A-level, who are learning basic scientific concepts from physics, chemistry, biology and Earth sciences, and linked to this, and (2) teachers communicating the results of Earth science research to students, (3) university students seeking to learn about the Earth system.

The origin of complex life and current loss of biodiversity have, in particular captured the public imagination. Evolution of life on Earth has captured significant public interest in the past and through popular books, television programs, and other publications. The importance of communicating the results of this research in the context of the "evolution of life on Earth" cannot be overstated. This broad topic serves to illustrate the fine balance on which the Earth's life rests. It is important to communicate to the public what the vast amount of time recorded in geologic history tells us, and how life and the workings of Earth are inextricable linked. Most importantly, it answers the question of "how we got here", informing the general public on issues such as evolution, the time scale of environmental change and how organisms adapt to it. Thus, the research results of this project stand to directly impact the information that is often disseminated to the public. We have identified three platforms:

The first platform targets teachers, students as well as the general public. Our plan is to introduce a workshop focused on ancient mass extinctions and current biodiversity crisis to the formal educational programme that is offered during the academic year by Our Dynamic Earth, an interactive science centre based in Edinburgh. With important feedback from the general public and students, the workshop will be molded to integrate with general science curricula for A-level and pre-A-level students so teachers may justify visits to Our Dynamic Earth. Importantly, the workshop will be one of as many as 20 that are offered continuously and viewed by as many as several thousand students and visitors per year. The long-term goal is to offer the workshop for 2-3 years, the average running time for most other science-based workshops at Our Dynamic Earth. This offers a direct and effective mechanism to disseminate the latest results and intellectual developments surrounding our research to a large group of students and teachers across the UK.

The second platform is through visual art. We have collaborated with freelance artist Alice Spicer to illustrate a UoE PhD thesis on the Permian Triassic extinction, entitled 'Why concern ourselves with the matter of the dead?' This work was designed to create material that includes the illustrations and lay summaries, to be displayed in the Cockburn Museum of the Edinburgh University, the Edinburgh Science Festival, and part of continued departmental outreach programmes with SESEF (Scottish Earth Science's Education Forum). The illustrations form a permanent component of the illustrator's personal portfolio that will on display in galleries, offering further opportunity to communicate the concepts of Earth Science research to a wider audience.

The third platform will target university students and researchers. We will make our Earth system box model freely available as an educational tool. We will develop an easy-to-use version of the model with a graphical user interface in the form of an executable program, and also implemented via a web java applet. This tool will be useful as an introduction to long term biogeochemical modelling for students and members of the general public. We will develop a series of lecture/practical plans that can be used with the model for undergraduate level courses to demonstrate the "process" of Earth system modelling with a focus on understanding changes in past climate and carbon cycling.