Ion probes support research into early life on Earth

Studies into agriculture, health and minerals are enabled by the flagship ion probe suite (NanoSIMS 50 and IMS 1280) and its dedicated engineer, Dr Matt Kilburn at the University of Western Australia (UWA).

2014 Future Fellow, Dr David Wacey, has used the ion probes extensively over many years to amass a significant body of work revealing the nature of some of the earliest life on Earth.

Dr David Wacey in the field.

When did life first appear on Earth, what form did it take and how can we recognise life on other planets? These are the big questions that interest Dr Wacey. The earliest life on Earth would have been very small, morphologically simple and probably only subtly different from co-occurring non-biological organic material. Fortunately, AMMRF (now Microscopy Australia)  instrumentation gives researchers a fighting chance to determine what is and what is not ancient fossilised life.

NanoSIMS ion image of a 1900 million-year-old pyritic Huroniospora microfossil: sulfur is blue; oxygen, representing quartz, is green; and nitrogen, pink. The discontinuous ring of nitrogen is interpreted as a chemical ghost of the original organic microfossil wall.

The UWA flagship has enabled Dr Wacey to collect unique in-situ elemental and isotopic data from rock samples up to 3.5 billion years old. This allows the precise ageing of the rocks and lets him associate the position of elements associated with life, such as carbon and nitrogen, with sulfur and structural features of potential fossils.

Ultrathin slices from potential microfossils were prepared so cell-wall microstructure and nanoscale chemistry could be studied by transmission electron microscopy, complementing the ion probe results. The flagship focused-ion beam instruments at the University of Adelaide and the University of New South Wales were used for this precision work. Accurate 3D models of the microbial fossils were also constructed using serial sectioning.

Dr Wacey’s research highlights

• He identified the earliest undisputed fossil life found so far on Earth (3.4 billion-year-old) and found that it had a sulfur-based metabolism, thought to be one of the earliest stages in the development of life.
• He found bacteria called Gunflintia caught in the act of being consumed by other bacteria. Their association with specks of the iron sulfide mineral, pyrite, strongly suggests that the pyritic sulfur originates from bacterial metabolism.
• He was part of a team that linked microbial activity with the formation of small iron oxide spheres on Earth. These spheres are very like structures found on Mars.
• He discovered that clay minerals are excellent at preserving cell structures, allowing him to see one billion-year-old cell membranes.
• He helped demonstrate that viruses can mediate the mineralisation of microbial matter and that many nanospheres in the geological record are likely to be fossilised viruses.
• Dr Wacey also wrote the first textbook on the subject: Early Life on Earth – A Practical Guide. As well as shedding light on the origins of life on Earth, these discoveries will help scientists to recognise what is and what is not extraterrestrial life.