PALEONTOLOGY: Enhanced: A New Molecular Window on Early Life Andrew H. Knoll In recent years, the boundary between the Archean and the Proterozoic--2500 million years ago--has been the boundary between a relatively well-studied biology preserved in fossils and a shadowland for paleobiological evidence for life on Earth. Brocks et al. now extend the chemical evidence for biomolecules from the previous 1700 million years to 2700 million years, by identifying biomarkers characteristic for cyanobacteria and eukaryotes in Archean rocks from rocks from Western Australia. The results show that a key attribute of eukaryotic physiology had already evolved 2700 million years ago. The author is at the Botanical Museum, Harvard University, Cambridge, MA 02138, USA. E-mail: aknoll@oeb.harvard.edu


Archean Molecular Fossils and the Early Rise of Eukaryotes Jochen J. Brocks, 12* Graham A. Logan, 2 Roger Buick, 1 Roger E. Summons 2 Molecular fossils of biological lipids are preserved in 2700-million-year-old shales from the Pilbara Craton, Australia. Sequential extraction of adjacent samples shows that these hydrocarbon biomarkers are indigenous and syngenetic to the Archean shales, greatly extending the known geological range of such molecules. The presence of abundant 2-methylhopanes, which are characteristic of cyanobacteria, indicates that oxygenic photosynthesis evolved well before the atmosphere became oxidizing. The presence of steranes, particularly cholestane and its 28- to 30-carbon analogs, provides persuasive evidence for the existence of eukaryotes 500 million to 1 billion years before the extant fossil record indicates that the lineage arose. 1 School of Geosciences, University of Sydney, Sydney, NSW 2006, Australia. 2 Australian Geological Survey Organisation (AGSO), Canberra, ACT 2601, Australia. * To whom correspondence should be addressed. E-mail: jochen.brocks@agso.gov.au or brocks@es.su.oz.au

This web site is provided for instruction in Botany and Zoology 342

by Kenneth G. Wilson,
Professor of Botany
Miami University
wilsonkg@muohio.edu