Field Pictures


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Trace fossil surfaces just above the Precambrian-Cambrian boundary, Grand Bank Head, Newfoundland




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A tiny Ediacaran frond, Newfoundland




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On a dig-site in Wyoming with a Camarasaurus.




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Sunrise over the Fayum Desert, Egypt


Alex Liu

Doctoral Student, Exeter College

Research Area: Oxygen and Ediacaran Evolution

Supervisors:
Prof. Martin Brasier (Oxford)
Prof. Duncan McIlroy (Memorial University of Newfoundland)

alexl[at]earth.ox.ac.uk

It is widely believed that many of the most notable and important events in Earth history occurred due to fluctuations in the levels of oxygen in the Earth's atmosphere [1]. These include mass extinctions [1] linked to drops in oxygen levels, the phenomenon of gigantism (e.g. in the Carboniferous) associated with high levels of oxygen [2], and the evolution and radiation of several groups of organisms. One of the most important and increasingly researched events is the initial evolution of metazoans, roughly 575 million years ago [3]. Geochemical studies indicate an oxygenation event in the deep oceans immediately following the Gaskiers glaciation, the last of the great Neoproterozoic 'Snowball Earth' events, and this is hypothesised to have driven the evolution of the Ediacaran fauna, which appear ~4 million years after the end of the glacial [4,5]. At present, there are few constraints on the actual values for the oxygen levels at this time, just a consensus that oxygen levels did rise.

My research is attempting to quantitatively determine the oxygen levels in the atmosphere, both over this time interval and across other important evolutionary boundaries where oxygen is suspected of having an influence, by taking a biological approach to the problem. There is potentially a relationship in groups of animals which respire by diffusion (e.g. some insects, amphibians), between their maximum size and the concentration of oxygen in their ambient environment [6]. I am attempting to quantify this relationship (measuring 'size' as the ratio of surface area to volume) for modern organisms, and then see whether the relationship can be taken back into the fossil record. Ultimately the plan is to determine the oxygen levels required to allow the survival of the largest organisms at certain periods of time (e.g. the early Ediacaran, or the Precambrian/Cambrian boundary), and compare these to the geochemical records to further constrain absolute oxygen concentrations. A similar study has been attempted for one Ediacaran fossil once before [7,8], but it is hoped that new techniques can improve on these estimates. These techniques include high-resolution laser scanning, computer modelling, and a comprehensive fieldwork programme incorporating Ediacaran sites in Newfoundland, England, Australia, China and Namibia, along with modern studies in the Black Sea.

This project is broad, incorporating within it ichnology, sedimentology, the geochemical evolution of the atmosphere through time, animal physiology and respiration, oceanic anoxic events, and the morphology, palaeontology and ecology of the earliest 'metazoan' fossils. This includes current work on the early life cycle of Ediacaran fronds, and studies into their respiration and metabolism. I hope that my research will be of interest to researchers in early life, atmospheric composition, general palaeontology and evolution, and even astrobiology.


Previous fieldwork interests include a trip to Wyoming, U.S.A., in conjunction with Iowa State University, where I assisted with several dinosaur excavations, helping teams including the Smithsonian Institute, and spent a few days in the Wyoming Dinosaur Center, learning various bone preparation techniques. I have also completed fieldwork in Egypt, in collaboration with Duke Lemur Center, for my Masters project 'determining the dietary and habitat adaptations of early proboscideans using stable isotope techniques'.

If you have any questions, queries or general comments, please get in touch using the above email address.


References
1. Berner, R. A., VandenBrooks, J. M. & Ward, P. D. Oxygen and Evolution. Science 316, 557-558 (2007).
2. Graham, J. B., Dudley, R., Aguilar, N. M. & Gans, C. Implications of the late Palaeozoic oxygen pulse for physiology and evolution. Nature 375, 117-120 (1995).
3. Narbonne, G. M. & Gehling, J. G. Life after snowball: the oldest complex Ediacaran fossils. Geology 31, 27-30 (2003).
4. Canfield, D. E., Poulton, S. W. & Narbonne, G. M. Late-Neoproterozoic deep-ocean oxygenation and the rise of animal life. Science 315, 92-95 (2007).
5. Fike, D. A., Grotzinger, J. P., Pratt, L. M. & Summons, R. E. Oxidation of the Ediacaran Ocean. Nature 444, 744-747 (2006).
6. Chapelle, G. & Peck, L. S. Polar gigantism dictated by oxygen availability. Nature 399, 114-115 (1999).
7. Runnegar, B. Oxygen requirements, biology and phylogenetic significance of the late Precambrian worm Dickensonia, and the evolution of the burrowing habit. Alcheringa 6, 223-239 (1982).
8. Runnegar, B. Precambrian oxygen levels estimated from the biochemistry and physiology of early eukaryotes. Palaeogeography, Palaeoclimatology, Palaeoecology 97, 97-111 (1991).

Publications
Liu, A. G. S. C., Seiffert, E. R. & Simons, E. L. Stable isotope evidence for an amphibious phase in early proboscidean evolution. PNAS 105, 5786-5791 (2008).

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