For the past century, most paleontological research has concentrated on sedimentary rocks deposited over the past 550 million years. It is now clear, however, that this conspicuous record of animals and plants documents only the latest 15% of the history of life on Earth. The earlier (pre-animal) biological record is written in the fossils of microorganisms, as well as in the chemical traces of microbial activity contained in sedimentary rocks. Rocks of Late Proterozoic age (900-550 million years) contain a rich fossil record that includes diverse planktonic algae and seaweeds, as well as bacteria of many kinds. The fossils indicate that this was a period of rapid evolutionary change. Chemical and geological data further suggest that the Late Proterozoic Earth was characterized by major changes in climate, tectonics, atmospheric chemistry, and the cycling of biologically important elements. In contrast, rocks of Early Proterozoic age (2500-1800 million years) reflect a very different world -- one in which an exclusively bacterial biota thrived in environments unaffected by the kinds of climatic and biogeochemical variability seen in the Late Proterozoic era. The key to understanding the transition from the Early Proterozoic Earth to the Late Proterozoic planet clearly must lie in rocks deposited during Middle Proterozoic times (1800- 900 million years). Careful field and laboratory studies will be conducted of the 1400-1300 million year of Bangemall Group, Western Australia -- a suite of rocks especially well suited to yield critical information on biological and environmental change during this period. Field measurements of the thickness, composition, and characteristic features of these rocks will be made; this will permit determination of the age and environmental relationships of the rocks. Samples collected within this matrix will be examined for their microfossil content, rock fabric and alteration history, and geochemistry (especially the ratios of the isotopes of carbon and strontium contained in certain of these rocks). The result will be a multidisciplinary data set that will provide critical insights into Middle Proterozoic biology and environments. Such data are of great importance in efforts to understand life's early evolution and how biology and Earth surface environments have influenced each other through time to produce the modern world. Although this research is basic in nature, it has important applications to mineral and petroleum exploration in Proterozoic rocks. Documentation of fossil and geochemical marker distributions will improve our ability to correlate Proterozoic rocks, the important first step in geological prospecting. A better understanding of Earth's environmental history will additionally serve to constrain patterns of exploration for the rich deposits of stratabound ores locked in Proterozoic sedimentary rocks.
