Rocks and sediments contain the chemical remains of the organisms that once lived in ancient oceans and lakes, just as they contain the mineral fossils with which we are all familiar. These ‘biomarkers’ can be used to reconstruct plant and animal assemblages living in past settings. Moreover, they can tell us something about the prevailing environment, since a biomarker’s distribution and isotopic composition can vary in organisms, depending on the surroundings in which they formed. For example, when chemical compounds called alkenones are recovered from ancient sediments, they can be used to estimate the sea-surface temperature of ancient oceans.
Chemists Richard Pancost and Bart van Dongen are using a technique based on the carbon isotopic composition of algal biomarkers to reconstruct changes in atmospheric carbon dioxide concentrations over the past 100 million years. This is a time when the Earth’s climate cooled considerably – a change thought to be driven in part by a decline in carbon dioxide concentrations. To try to pin down the timing and extent of this decline, they have teamed up with geologists to recover sediments from Tanzania that contain exceptionally well-preserved bio-markers. Results from this work will help them to better understand how current rates of change compare with those in the past.
This project is funded by the Natural Environment Research Council in collaboration with the Tanzanian Petroleum Development Corporation.