Evidence from fluid inclusions for microbial methanogenesis in the early Archaean era

Abstract

Methanogenic microbes may be one of the most primitive organisms, although it is uncertain when methanogens first appeared on Earth. During the Archaean era (before 2.5 Gyr ago), methanogens may have been important in regulating climate, because they could have provided sufficient amounts of the greenhouse gas methane to mitigate a severely frozen condition that could have resulted from lower solar luminosity during these times. Nevertheless, no direct geological evidence has hitherto been available in support of the existence of methanogens in the Archaean period, although circumstantial evidence is available in the form of approximately 2.8-Gyr-old carbon-isotope-depleted kerogen. Here we report crushing extraction and carbon isotope analysis of methane-bearing fluid inclusions in approximately 3.5-Gyr-old hydrothermal precipitates from Pilbara craton, Australia. Our results indicate that the extracted fluids contain microbial methane with carbon isotopic compositions of less than -56 per thousand included within original precipitates. This provides the oldest evidence of methanogen (> 3.46 Gyr ago), pre-dating previous geochemical evidence by about 700 million years.

A methanogen hosted the origin of the genetic code

“…This is compatible with the suggestion that methanogenesis is a very early pathway in the history of life (Brocks et al, 1999;Battistuzzi et al, 2004;Bapteste et al, 2005;Ueno et al, 2006). Finally, this observation also corroborates the hypothesis that the LUCA was a methanogen (Xue et al, 2005;Wong et al, 2007).…”

“…Geological and biological methods aiming to establish the antiquity of biological processes: the example of methanogenesis Geological evidence suggest that methanogenesis was one of the earliest biological processes to take place on earth (Brocks et al, 1999;Ueno et al, 2006). Nevertheless, it is unclear how 'early' this origin was because, as geological dating indicates methanogenesis taking place approximately 3.5 billion years ago (Ueno et al, 2006), methanogenesis might actually be biologically later in the sense that the very first forms of life, and in particular the last universal common ancestor (LUCA), might be non-methanogenic 'organisms'. It is therefore clear that geological fossils need to be accompanied by biological evidence if we are to more accurately define the timing of biological processes.…”

An archaeal origin of eukaryotes supports only two primary domains of life

“…An earlier origin for eukaryotes had been suggested on the basis of the presence of sterane biomarkers in 2.7-billion-year-old rocks 77 , but these were subsequently shown to be contaminants from younger rocks 78,79 . An early origin for Archaea has been inferred on the basis of the presence of biological methane, today produced only by methanogenic Euryarchaeota, in rocks that are 3.5 billion years old 80 . Analyses of microfossils and stromatolites-modern versions of which harbour complex bacterial communities 81 -in 3.4-billion-year-old rocks suggest the presence of photosynthetic bacteria [82][83][84] .…”

La vida temprana en la Tierra y los primeros ecosistemas terrestres

“…La presencia de microfósiles, microbialitas, y biomarcadores moleculares e isotópicos en rocas de más de 3000 Ma, indican que la vida microbiana era abundante en ambientes marinos, someros y profundos del Arqueano (Lowe, 1980;Walter et al, 1980;Awramik et al, 1983;Schopf, 1983;Walter, 1983;Walsh y Lowe, 1985;Rasmussen, 2000;Westall et al, 2001;Furnes et al, 2004;Shen y Buick, 2004;Tice y Lowe, 2004;Allwood et al, 2006;Banerjee et al, 2006;Westall et al, 2006aWestall et al, , 2006bUeno et al, 2006;Schopf et al, 2007 y referencias incluidas;Shen et al, 2009;Westall, 2010;Wacey et al, 2011). Ello apoya la idea de que las zonas costeras estuarinas fueron muy productivas en aquel tiempo, y que la fotosíntesis ya estaba operando (Awramik, 1992;Rosing y Frei, 2004;Tice y Lowe, 2004;Buick, 2008;Hoashi et al, 2009;Kato et al, 2009;Kendall et al, 2010), aunque tal vez no necesariamente oxigénica (Westall et al, 2011;Li et al, 2012).…”

“…Los fósiles tipo eucarionte más antiguos (acritarcos, Buick, 2010), que quizás requerían oxígeno para maximizar sus capacidades energéticas y metabólicas, tienen ~3200 Ma de edad y también estuvieron presentes en ambientes estuarinos (Javaux et al, 2010). A pesar de desconocer su verdadera identidad, la presencia de microfósiles de gran tamaño (> 150 µm de diámetro celular) indica que la vida se diversificó y alcanzó una presencia global relativamente rápido (Kandler, 1994;Altermann y Schopf, 1995;Ueno et al, 2006;Blank, 2009;David y Alm, 2011), y ocupó una amplia variedad de nichos ecológicos hacia el Paleoarcheano, incluso en lugares gravemente perturbados por impactos de asteroides (ver Walsh, 1992 y referencias incluidas). Una mayor diversidad, ubicuidad, y abundancia biológica aparece más adelante en el tiempo, en el Proterozoico tardío (i.e.…”