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Drilling Update

The Emergence of Microbial Life in Archean Pillow Lavas

This is the abstract of a seminar given by Nicola McLoughlin, during a month-long stay in South Africa at AEON September 2009.

Photomicrograph of microbial biotextures in a surface sample of inter-pillow...
Photomicrograph of microbial biotextures in a surface sample of inter-pillow breccia from the Hooggenoeg Complex of the Barberton Greenstone belt. The meta-volcanic glass comprises a greenschist facies assemblage of chlorite and quartz with titanite filled tubular textures. These are curvi-linear, unbranched and radiate from a central band of micro-crystalline titanite. Some taper towards their ends and are segmented by cross-cutting chlorite. These textures are interpreted to be mineralized tunnels created by microbes that etched volcanic glass on the Archean sub-seafloor. This is a composite z-stacked image showing tubes found at different focal depths. Scale bar 50μm.
Foto:
Nicola McLoughlin

Microbial activity in volcanic glass creates micron-scale granular and tubular cavities that can be regarded as trace fossils. These are ubiquitous in pillow lavas of the upper in-situ oceanic crust, spanning the youngest to the oldest oceanic basins (0 to 170 Ma) and have been attributed to the actions of microbial groups including Fe and Mn oxidizing bacteria. Comparable, mineralized micro-textures are also found in meta-volcanic glasses from ophiolites and Precambrian greenstone belts, including the Barberton Mountain Land of South Africa. Multiple lines of evidence suggest that these ~3.5 billion year old micro-textures from the Hooggenoeg Formation of S Africa were also formed by the microbial etching of formerly glassy lavas suggesting that life emerged in the sub-seafloor.

The talk reviewed the morphological similarities between the Archean micro-textures and bioalteration textures found in modern volcanic glasses. The chemical, isotopic and microbiological evidence that supports a microbial origin for the alteration of Archean volcanic glass were presented. Lastly McLoughlin explored the potential for discovering microbial bioalteration textures on Mars.

Read more about Dr. Nicola McLoughlin and about the drilling field work in South Africa.

Read more about McLoughlin's stay at AEON (African Earth Observatory Network) in South Africa.

Some of the results of their work on the core from Barberton were presented at the Geological Society of America's conference last autumn 2010 in a session where Harald Furness was a co-convenor.

 

Suggested Reading:
Furnes et al. (2004) Early life recorded in Archean pillow lavas. Science 304, 578–581
McLoughlin et al. (2009). Ichnotaxonomy of microbial trace fossils in volcanic glass. J. Geol. Soc. Lon. 166, 159-169