North China craton: A unique window into Earth's middle age

Biological evolution is commonly viewed as a gradual and largely predictable journey from simple, single-celled bacterial ancestors, to ever larger and more complex life forms. Similarly, the evolution of Earth's atmosphere and oceans (which is considered to play a crucial role in biological evolution) is generally viewed as a gradual, albeit stepwise, trajectory towards greater oxygenation, with each rise occurring in tandem with, and facilitating progressive increases in, biological size and complexity. This paradigm of a monotonous progression towards modern conditions and the implied linkage between key evolutionary steps and oxygenation has recently been challenged. However, relevant data to resolve the issue are scarce and ambiguous. Geochemical estimates of atmospheric oxygen levels during the Proterozoic range widely, and our understanding of ocean oxygenation levels have complicated this picture further, indicating a dynamic environment fluctuating between abundant oxygen levels and no oxygen (anoxic). As such, links between Earth surface oxygenation and early biological evolution have been particularly difficult to unravel. Recently discovered, large eukaryote fossils from North China are particularly difficult to understand in the light of current understanding of Earth's atmospheric evolution which suggests exceedingly low oxygen levels at this time of diversification.

Studies of early Earth environments have been severely hampered by the poor quality of geological samples (burial and subsequent exposure at the Earth's surface can destroy the primary geochemistry of rocks). With this in mind, we propose a multidisciplinary study of superbly preserved mid-Proterozoic samples from the North China craton, largely obtained by drilling, to reconstruct the oxygenation history of the ocean and to investigate how nutrients in the ocean interact with this history. This will be combined with new paleontological data to demonstrate how nutrients and redox constrained the early evolution of eukaryotes, the ancestral lineage of all extant animals. By specifically targeting the best quality samples that can be obtained across this crucial interval in the history of life on Earth, the research outlined in this proposal will shed fundamental new insight into the enigmatic mid-Proterozoic Earth system, including why it took so long for large, complex multicellular eukaryotes to dominate marine ecosystems.

In this project we propose an integrated approach to test assumed linkages between Earth surface conditions and biological evolution during the mid-Proterozoic (~1.7-0.9 Ga). A combination of fieldwork and targeted shallow drilling of demonstrably preserved rocks on the North China craton will provide the basis for a detailed study of a crucial interval of early biological diversification. In particular, we will utilize key redox and novel nutrient tracers, organic-walled fossils and molecular biomarkers. Reconstruction of early marine ecosystems and their environment will allow us to test highly topical hypotheses relating to the delayed evolution of biological complexity on Earth, including the potential roles of nutrient availability and Earth surface oxygenation.

We have identified the following potential beneficiaries and ways in which they could benefit from the project:

School children: Through this project we will have access to some remarkable new 'megascopic' and micro-fossils from the North China craton. Many of the new examples have not been described by science, and present an exciting puzzle to reconstruct what they were, what they did, and what sort of communities they formed. School children could benefit from exposure to this fossil material and the environmental puzzles it raises through an interactive education display/exhibit that is brought to them or is available in a museum that they visit.

Undergraduate students: The Precambrian Earth system is a much overlooked subject in university courses despite covering almost 90% of all Earth history. The three UK-based investigators on this project all teach Precambrian Earth history at UCL, Leeds and Exeter universities. Hence undergraduates at these universities could benefit from the new material being brought into the teaching of the investigators.

Graduate students: Earth system science PhD students could benefit from exposure to the new research and engagement with it. For example, in July 2014, PI Shields-Zhou, Co-I Poulton, PP Zhu and PP Ling convened a workshop for graduate students and early career researchers in Nanjing, which attracted around 50 students from China, UK and USA. The association of PhD students with the project, and a further such workshop, are pathways through which graduate students could benefit.

General public: Our project concerns the earliest eukaryotic origins of animals, plants and fungi, and so is a topic of intrinsic interest to the general public. Life's early origins have featured prominently in recent TV and radio documentary series, from David Attenborough's 'Early Life' to widespread coverage of 'Snowball Earth' in various forms. The general public could benefit in several ways from the project. The new 'world record' fossils, stromatolites and example drill-core (with data) could form part of a museum exhibit. They could also from the focus of popular science articles and/or TV/radio documentaries. The drilling represents an ideal opportunity for real-time engagement with the general public through blogs, twitter and other web-based social media. Public lectures could be given by the two UK-based investigators, who have considerable experience in giving lectures for school groups, school teachers and the lay public. A dedicated website would also provide access to the project activities.

Geoscience industries: The global petroleum industry has become increasingly interested in Proterozoic oil and gas, as the more conventional Phanerozoic sources of natural fuel become exhausted (e.g., Craig et al., 2013, The palaeobiology and geochemistry of Precambrian hydrocarbon source rocks, Marine and Petroleum Geology, v. 40, p. 1-47). The North China craton has long been of major interest to the petroleum industry due to the unusually organic-rich and unmetamorphosed nature of the Yanshan Basin. Despite such interest, relatively little is known about the organic geochemistry of Proterozoic hydrocarbons, and much of what has been discovered is protected by both nationalised and private petroleum companies. At present the oldest 'live' oil is from ~1.4 Ga in Australia, while the oldest commercial operations focus on mid-late Neoproterozoic source rocks. We thus anticipate that our work on the early Mesoproterozoic interval, circa 1.6-1.4 Ga, in North China will be of considerable interest for conventional and oil shale petroleum industries. They could benefit from early access to our results, mediated, for example through the Geological Society of London Petroleum Specialist Interest Group, or through Getenergy.Ltd (see getenergyawards.com).