[asa] Direct dating of Archean microbial ichnofossils to 3.35 Ga

From: Rich Blinne <rich.blinne@gmail.com>
Date: Thu Jun 07 2007 - 00:30:06 EDT

http://www.gsajournals.org/perlserv/?request=get-abstract&doi=10.1130%
2FG23534A.1

> Geology
>
> Article: pp. 487490 | Full Text | PDF (369K)
> Direct dating of Archean microbial ichnofossils
>
> Neil R. Banerjee1, Antonio Simonetti2, Harald Furnes3, Karlis
> Muehlenbachs4, Hubert Staudigel5, Larry Heaman6, and Martin J. Van
> Kranendonk7
>
> 1. Department of Earth Sciences, University of Western Ontario,
> London, Ontario N6A 5B7, Canada, 2. Department of Earth and
> Atmospheric Sciences, University of Alberta, Edmonton, Alberta T6G
> 2E3, Canada, 3. Centre for Geobiology and Department of Earth
> Science, University of Bergen, Allegaten 41, 5007 Bergen, Norway,
> 4. Department of Earth and Atmospheric Sciences, University of
> Alberta, Edmonton, Alberta T6G 2E3, Canada, 5. Scripps Institution
> of Oceanography, University of California, La Jolla, California
> 92093-0225, USA, 6. Department of Earth and Atmospheric Sciences,
> University of Alberta, Edmonton, Alberta T6G 2E3, Canada, 7.
> Geological Survey of Western Australia, 100 Plain Street, East
> Perth, Western Australia 6004, Australia
>
>
> Well-preserved Archean pillow lavas from the ca. 3.35 Ga Euro
> Basalt of the Pilbara Craton, Western Australia, contain micron-
> sized tubular structures mineralized by titanite (CaTiSiO4) with
> residual organic carbon preserved along their margins. Direct U-Pb
> dating of titanite in the tubular structures demonstrates an
> Archean age. These tubular microstructures are identical to
> microbial ichnofossils in modern basalts, ophiolites, and
> greenstone belts, and are interpreted as a biogenic signature in
> these ancient rocks. Microbial colonization of basaltic glass thus
> appears to have been part of a deep subsurface biosphere
> established early in Earth's history.
>
> Keywords: early life, greenstone belt, Pilbara Craton,
> geochronology, ichnofossil, astrobiology
>

Nature summarized this as:

> Radiometric dating has confirmed that microscopic tubular
> structures in ancient lavas date back billions of years. These
> structures are thought to show that life thrived in volcanic rocks
> deep within the early Earth.
>
> Neil Banerjee of the University of Western Ontario in London,
> Canada, and his colleagues found the microfossils in pillow lavas
> in the Pilbara Craton of western Australia. The tubes contain
> traces of organic carbon, and appear identical to those left in
> basaltic rocks by modern microbes.
>
> The tubular structures at this site also contained the mineral
> titanite, which allowed them to be dated by measuring trace amounts
> of lead and uranium. This revealed the structures to be 3 billion
> years old.

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Received on Thu Jun 7 00:30:34 2007

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