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
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wilsonkg@muohio.edu