Fossilised bacteria offer clues to the origins of life

A visiting expert on fossilised bacteria has been using University of Cape Town's (UCT) scanning electron microscope (the UCT scanning electron microscope is capable of a resolution of 3nano meters, i.e. 3x10-10m) to study what may represent the origins of life on Earth, and the possibility of life on Mars.

Dr Frances Westall is a marine geologist based at the University of Bologna. A UCT PhD graduate, she travels widely, following her special interest in the tiny fossils. She first found fossilised bacteria in cores recovered from the ocean floor while undertaking oceanographic research some years ago on the Joides Resolution, the drilling research vessel which visited Cape Town recently.

Since then, she has pursued her interest in bacteria fossils relentlessly. She visited UCT to study fossilised bacteria found in rocks from Barberton, Mpumalanga in South Africa. South Africa's geological history spans approximately 3.7 billion years. The oldest rocks are found in the Kaapvaal craton, which underlies the north-eastern part of the country. Kaapvaal craton consists of archaean granites and gneisses and lesser volumes of metamorphosed volcano sedimentary greenstone lithologies. Although the granite gneiss terrains are less mineralised and host small pegmatitic, corundum and gold deposits, the greenstones host gold, antimony, copper-zinc, asbestos, talc, mercury, magnesite and gemstone deposits. The Barbeton greenstone belt is the largest gold-producing greenstone belt in South Africa, while the Murchison Belt is an important source of antimony. The large sedimentary basins, which developed on the Kaapvaal craton, host some of the richest mineral resources in the country. The Witwatersrand Supergroup sediments were deposited between 3074-2714 million years ago in a basin measuring 320 by 160 kilometers south of present-day Johannesburg. Similar strata, which also host small gold deposits, were deposited as the Pongola and Pietersburg Groups. The volcano-sedimentary rocks of the Ventersdorp Supergroup host gold concentrations on the contact with the Witwatersrand Supergroup. It is in the Barbeton greenstone belt that fossil bacteria have been found. The rock is ancient - between 3,3 and 3,5 billion years old - which places the fossils among the oldest known life forms on earth.

Dr Westall has also taken a keen interest in evidence which suggests that life could be found on Mars. In April this year, she visited scientists at NASA in the United States where she discussed a meteorite found in Antarctica, said to come from the red planet. The meteorite has attracted international attention because of claims that it contains evidence of fossilised bacteria, suggesting that life may exist on Mars. Dr Westall brought a tiny sample of the "Mars Rock" to UCT to study it using the scanning electron microscope, along with the rocks from Barberton. She is comparing the samples, and hopes to find evidence that will prove or disprove signs of fossilised life in the meteorite. She will join the NASA Mars Rock research team early next year, funded by a research fellowship from the space agency.

Dr Westall was born in South Africa, and grew up in Britain. She completed her first degree in geology at the University of Edinburgh. After graduating with a PhD in marine geology at UCT, she joined the Alfred Wegener Institute for Marine and Polar Research at Bremerhaven, Germany. Her research interest at the time was the oceanography of the South Atlantic, particularly sedimentology.

"While on the Joides Resolution, I found my first fossilised bacteria, just by chance, in sediments. We were taking very long drill cores. In one of the cores I saw these structures which looked really weird to me, and they turned out to be fossilised bacteria."

Her new-found interest took her to Professor Claude Monty of the University of Liege, Belgium, an expert in fossilised bacteria. She also worked with him in France when he moved to the University of Nantes. The European Community awarded Dr Westall a grant which enabled her to move to Italy to continue her research, focussing on the fossilising process. She recovered bacteria from the deep sea of the South Atlantic and fossilised them herself to learn more about the processes involved.

These experiments provided useful for further studies of bacteria fossils in rock, and she has found fossils about 49 to 50 million years old in collaboration with researchers in Germany. She contacted Professor Maarten de Wit of UCT's Department of Geological Sciences because she wanted to study the earliest known bacteria fossils. Prof De Wit has been working in the Barberton area which has some of the oldest known rocks on earth.

Dr Westall said the geology of Barberton was significant because the area sits on an ancient piece of the earth's crust which has been left relatively unscathed by the tremendous forces of continental movement. Prof De Wit is also very interested in evidence of life in the rocks, because they were formed by ancient hotsprings of the type found in deep oceans today. Most earth scientists now believe that early life thrived in hot springs of this type, and may have originated from them. He is studying the rocks of the area, thanks to a research grant from the Foundation for Research Development (FRD).

Dr Westall collected Barberton rock samples from UCT last year, to study them in Europe, and returned this year to investigate them further using the scanning electron microscope. She is looking for structures which have the same size and shape as modern bacteria and present the same kind of characteristics. Like modern bacteria, fossilised bacteria are typically found in clusters, or colonies. The fossilised bacteria can often be found in fossilised slime. Modern bacteria often occur in a layer of slime, because it provides protection, a source of nutrients, and a way of attaching them to a substrate.

Dr Westall said the fossilised bacteria were typically between one and two microns in size (one micron is 1000th of a millimetre). Scientists have used conventional microscopes to study the fossils. However, these microscopes did not provide the resolution necessary to get a clear picture of the bacteria, particularly when studying samples in thin sections, she said. The scanning electron microscope now makes it possible to study the shape, size and form of the fossilised bacteria, while also providing analytical data on the chemistry of the sample.

Dr Westall described the similarities between the fossilised bacteria in the Barberton rock and modern bacteria as "stunning". "I felt I was looking at modern bacteria. It's just amazing."

She also found it interesting to note that the fossils represented advanced forms of life , in spite of the age of the rock. While signs of the origin of life remain elusive, the bacteria may well have been the only life forms present at the time of the formation of the ancient rocks. The scanning electron microscope also revealed structures that were smaller than modern bacteria. "We are wondering if these are just small forms of bacteria. We are getting a lot more information, but we can't interpret this yet," she said. However, what they had found so far "is quite fundamental to the search for life on earth".

Meanwhile, she also used her time on the scanning electron microscope to study the characteristics of her "Mars Rock" sample, with a view to proving or disproving the possibility of life forms in the meteorite. Scientists believe the meteorite came from Mars because it contains bubbles of gas which match the chemical composition of the atmosphere of the planet. The rock was formed about 4,5 billion years ago and probably circled the solar system for several million years before landing on earth. It contains carbonate minerals, which suggest the presence of liquid water on Mars, which in turn points to the possibility of life.

"The carbonate globules are more or less the same age as the rocks at Barberton (3,5 billion years), so we want to compare the structures that we see in the carbonate globules with the structures that we see in the Barberton rock," Dr Westall said. "There is quite a lot of work involved. We are hoping to prove or disprove the possibility of fossil bacteria or other fossilised life forms." Dr Westall said the issue of whether or not the Mars Rock contained fossils was highly controversial. Scientists could not agree on how the carbonate globules came to be in the rock, and on whether marks found in the rock could indicate fossilised life forms. "I spent a few days with the people who are studying them at NASA in April, looking through all their photographs and discussing what the marks might or might not be." "Most of the structures I saw looked crystalline. A few didn't. A few looked like squiggly bacteria." Dr Westall said she would like to study more examples before expressing an opinion on whether or not they represented life forms.

She said the "s"-shaped marks claimed to be bacteria were long and thin, and were unlike the fossils she studied in rocks from Earth, which tended to be oval, the shape of short-grained rice. Dr Westall said that while the nature of this work bordered on science fiction, it was fascinating to speculate about the origins of life on earth, and possibly the universe. If they found evidence of independent life on Mars, it raised the possibility of life on other planets in the universe.