David Wacey

Research Interests:

My research seeks to elucidate how and when life originated on Earth and whether it could have originated on other planets such as Mars. Within this framework, I am part of a multidisciplinary team based jointly at the Centre for Microscopy, Characterisation & Analysis and the School of Earth & Environment, here at the University of Western Australia.

I use a variety of research tools, including field based mapping and sample collection in Australia, optical and scanning electron microscopy, state of the art computer based imaging, microbiology and high resolution geochemistry.

Current Research Projects:

Questions concerning the origins of life and of our place in the universe are fundamental to modern science and society. Locating the first evidence for life on Earth is, however, a question of considerable complexity - multiple lines of evidence are essential. These include a well-constrained and plausible geological context, geochemical evidence for biology-like metabolic pathways, evidence for biology-like morphology, plus testing against plausible non-biological origins. This means that features until recently regarded as the earliest microfossils or biogeochemical signals at 3.8-3.0 billion years old should not be accepted as biological until their origin from plausible non-biological processes has been examined and can be falsified.

2. What was Earth like 3.0-4.0 billion years ago and what habitats were most conducive for the origin of life?

I have been searching for new and more reliable windows into the earliest fossil record, and have accordingly pioneered the exploration of early Archaean siliclastic sandstones. These differ from commonly investigated stratiform cherts in suffering less displacement or replacement by later silica phases, and provide the additional advantages of contrasting grain compositions, preserved grain boundaries, plus cements and sedimentary structures. They are altogether more readily measured and visualized as ancient microbial habitats than are stratiform cherts. Even so, it is clearly essential to be able to distinguish abiogenic from biogenic structures, as I have been attempting with studies of criteria for biogenicity in endolithic microborings and by ongoing research into ambient inclusion trails in sand grains. My latest field work has found that early Archaean sandstones can preserve cell- and sheath-like structures caught up within early diagenetic and possibly meteoric cements, plus the preferential formation of microtubes within sulphide grains.

3. The interplay between microbes and minerals both in modern and ancient settings.

I am also interested in the way microbes modify ambient conditions to form minerals at the present day. I then apply these findings to try to solve geological problems. My D.Phil. thesis concentrated on the so called ‘dolomite problem’. The ‘dolomite problem’ had resulted from the inability to precipitate dolomite (Ca0.5Mg0.5CO3) in the laboratory under earth surface temperatures and pressures, together with the enigma of the relative scarcity of modern occurrences of the mineral despite seawater being supersaturated with respect to dolomite. My work helps to address this problem by approaching it from a kinetic rather than purely thermodynamic viewpoint, in particular focusing on the role of sulphate-reducing bacteria (SRB) in modifying ambient water chemistry. I used laboratory experiments together with data collected in the field from the Coorong region of South Australia to test an organogenic model for dolomite precipitation. I found that dolomite could be precipitated under ‘normal’ earth surface conditions catalysed by organic material and SRB. This model could be significantly more important in dolomite genesis than previously thought.

Recent Publications:

WACEY, D., McLoughlin, N. and Brasier, M.D. (2008) The search for windows into the earliest history of life on Earth and Mars. In: Seckbach, J. and Walsh, M. (Eds.) From Fossils to Astrobiology: Cellular Origin, Life in Extreme Habitats and Astrobiology 11, 548p. Take a look

WACEY, D., Kilburn, M.R., McLoughlin, N., Parnell, J., Stoakes, C.A. and Brasier, M.D. (2008) The enigma of ambient inclusion trails and biological activity in a ~3400 Ma sandstone. Journal of the Geological Society of London 165, 43-53.

WACEY, D., Kilburn, M.R., Stoakes, C.A., Aggleton, H. and Brasier, M.D. (2008) Ambient inclusion trails: Their recognition, age range and applicability to early life on Earth? In: Dilek, Y., Furnes, H. and Muehlenbachs, K. (Eds.) Links Between Geological Processes Microbial Activities & Evolution of Life, Springer, 113-134.

WACEY, D., Wright, D.T. and Boyce, A.J. (2007) A stable isotope study of microbial dolomite formation in the Coorong region, South Australia. Chemical Geology 244, 155-174.

McLoughlin, N., Brasier, M.D, WACEY, D, Green, O.R. and Perry, R.S. (2007) Formulating Biogenicity Criteria for Endolithic Microborings on Early Earth and Beyond. Astrobiology 7, 10-26.

WACEY, D., McLoughlin, N., Green, O.R., Parnell, J. Stoakes, C.A. and Brasier, M.D. (2006) The ~ 3.4 billion-year-old Strelley Pool Sandstone: a new window into early life on Earth. Int. J. Astrobiology 5, 333-342.

Brasier, M.D., McLoughlin, N., Green, O.R. and WACEY, D. (2006) A fresh look at the fossil evidence for early Archaean cellular life. Phil. Trans. R. Soc. B 361, 887-902.

Wright, D.T. and WACEY, D. (2005) Precipitation of dolomite using sulphate-reducing bacteria from the Coorong Region, South Australia: significance and implications. Sedimentology 52, 987-1008.

Perry, R. S., Kolb, V. M., Philip, A. I., Lynne, B. Y., McLoughlin, N., Sephton, M., WACEY, D. and Green, O. R. (2005) Making silica coatings in the lab: synthetic desert varnish. In: Hoover, R. B., Levin, G. V., Rozanov, A. Y. and Randall Gladstone, G. (Eds) Astrobiology and Planetary Missions: Proc. S.P.I.E. 5906, pp 265-275.

Wright, D.T. and WACEY, D. (2004) Sedimentary dolomite: a reality check. In: Braithwaite, C.J.R., Rizzi, G. & Darke, G. (Eds) The geometry and petrogenesis of dolomite hydrocarbon reservoirs. Spec. Pub. Geol. Soc. Lon. 235, 65-74.