T20 Changes in Ocean and Atmospheric Redox State and the Evolution of Life I

Sunday, 22 October 2006
8:00 AM - 12:00 PM

PROGRESS TOWARDS AN UNDERSTANDING OF BIOGENESIS

Paper number: T20-13
Program: Technical Sessions
Time: 11:10 AM – 11:25 AM

Authors

Abstract

Since antiquity human societies have attempted to understand biogenesis. It was, however, Darwin, who in 1859, set the course of modern science when he proposed his “genealogical tree” of “the great kingdoms of nature” which pointed back in time to a common ancestor for all life on Earth. Darwin's ideas took on much greater meaning in the last half of the 20th century with the decipherment of the genetic code and the refinement of the deepest roots of the tree of life. The realization that many of the life forms occupying the deepest roots of the tree of life were hyperthermophiles led to the conclusion that biogenesis may have occurred in and around high temperature hydrothermal vents. Numerous models for various stages in biogenesis have been developed on the basis of these conclusions. Most are based on data derived from the modern biosphere and are thus limited. Modern organisms, whilst inheriting an ancient genetic legacy have been shaped by billions of years of evolution. The only real record of biogenesis and the environment of prebiotic Earth is preserved in the ancient rock record.

Evidence of hydrothermal activity is widespread in Earth's earliest rock record, especially so on the Archean Pilbara Craton of Western Australia. Over the past seven years we have mapped and sampled three of the earliest of these well-preserved hydrothermal systems preserved in rocks ranging in age from 3.5 to 3.4 Ga. Black carbonaceous cherts are abundant in these early rocks and have been shown to extend to paleo-depths of as much as two kilometres in the hydrothermal system. Preliminary analysis of the carbonaceous components of cherts from hydrothermal veins and bedded sediments using Ultra-Microprobe Two-Step Laser Mass Spectrometry show that a variety of low molecular weight compounds are preserved. The results, following multivariate analysis, will lead to the identification of robust organic signatures, both prebiotic and biotic, that have survived the extremes of thermal maturation over a vast time period. The data will ultimately help define the environment of prebiotic Earth that led to biogenesis and provide an objective basis for modeling biogenesis.