Archean rocks (2.5 to 4 billion-years-old) can record traces of the activity of the first living organisms as well as information about the environment in wich primitive life evolved. However, analyzing such evidences is often difficult because of the rocks age and the similarity of the signatures that can be produced by biological and geological processes. New analytical strategies must therefore be developed.
Synchrotron beam, because of its spatial resolution and high sensitivity, is particularly well-adapted for the study of micrometer-size, fragile objects embedded in mineral matrices.
A combination of different spectroscopical techniques, most of which use a synchrotron beam, were used to determine the biogenicity of recent microfossils. Furthermore, micro-XANES results suggest that the fossilized organisms probably metabolized sulfur. The analytical protocol described here can be applied to older microfissils in order to asses their biogenicity and study the metabolism of fossilized organisms.
Archaean (3.5 billion-years-old) fluid inclusions from the North Pole Dome, Pilbara, Australia, were analyzed by synchrotron X-ray microfluorescence. Results show thaht inclusions, trapped in intra-pillow basalt quartz pods, contain a fluid close to North Pole seawater mixed with mantle-buffered fluids. Chlorine and bromide composition of these fluids suggest that biological activity influenced the composition of seawater. In addition, carbonaceous globules of probable (yet not ascertained) biological origin were identified in North Pole sediments. Finally, the very low sulfate content in North Pole seawater end-member indicates that the O2 concentration in the Archaean atmosphere was very low.