Oxygenic photosynthesis is widely accepted as the most important bioenergetic process happening in Earth's surface environment. It is thought to have evolved within the cyanobacterial lineage, but it has been difficult to determine when it began. Evidence based on the occurrence and appearance of stromatolites and microfossils indicates that phototrophy occurred as long ago as 3,465 Myr although no definite physiological inferences can be made from these objects. Carbon isotopes and other geological phenomena provide clues but are also equivocal. Biomarkers are potentially useful because the three domains of extant life-Bacteria, Archaea and Eukarya-have signature membrane lipids with recalcitrant carbon skeletons. These lipids turn into hydrocarbons in sediments and can be found wherever the record is sufficiently well preserved. Here we show that 2-methyl-bacteriohopanepolyols occur in a high proportion of cultured cyanobacteria and cyanobacterial mats. Their 2-methylhopane hydrocarbon derivatives are abundant in organic-rich sediments as old as 2,500 Myr. These biomarkers may help constrain the age of the oldest cyanobacteria and the advent of oxygenic photosynthesis. They could also be used to quantify the ecological importance of cyanobacteria through geological time.

The molecular and isotopic compositions of lipid biomarkers of cultured Aquificales genera have been used to study the community and trophic structure of the hyperthermophilic pink streamers and vent biofilm from Octopus Spring. Thermocrinis ruber, Thermocrinis sp. strain HI 11/12, Hydrogenobacter thermophilus TK-6, Aquifex pyrophilus, and Aquifex aeolicus all contained glycerol-ether phospholipids as well as acyl glycerides. The n-C 20:1 and cy-C 21 fatty acids dominated all of the Aquificales, while the alkyl glycerol ethers were mainly C 18:0 . These Aquificales biomarkers were major constituents of the lipid extracts of two Octopus Spring samples, a biofilm associated with the siliceous vent walls, and the well-known pink streamer community (PSC). Both the biofilm and the PSC contained mono-and dialkyl glycerol ethers in which C 18 and C 20 alkyl groups were prevalent. Phospholipid fatty acids included both the Aquificales n-C 20:1 and cy-C 21 , plus a series of isobranched fatty acids (i-C 15:0 to i-C 21:0 ), indicating an additional bacterial component. Biomass and lipids from the PSC were depleted in 13 C relative to source water CO 2 by 10.9 and 17.2‰, respectively. The C 20-21 fatty acids of the PSC were less depleted than the iso-branched fatty acids, 18.4 and 22.6‰, respectively. The biomass of T. ruber grown on CO 2 was depleted in 13 C by only 3.3‰ relative to C source. In contrast, biomass was depleted by 19.7‰ when formate was the C source. Independent of carbon source, T. ruber lipids were heavier than biomass (؉1.3‰). The depletion in the C 20-21 fatty acids from the PSC indicates that Thermocrinis biomass must be similarly depleted and too light to be explained by growth on CO 2 . Accordingly, Thermocrinis in the PSC is likely to have utilized formate, presumably generated in the spring source region.Based on phylogenetic analysis of small-subunit rRNA sequences, hyperthermophilic organisms proliferate in the deepest branches of the Bacterial and Archaeal domains. The branch lengths of these hyperthermophilic lineages tend to be short, which further suggests that such organisms are the closest known extant descendants of the last common ancestor and retain many ancestral phenotypic properties (49). The recent discovery of filamentous microfossils preserved in a 3,235-million-year-old submarine volcanogenic deposit lends considerable weight to the theory that hydrothermal vent organisms have had a very long history on Earth (41). Hyperthermophilic microbes are also attracting astrobiological and biogeochemical interest because of their potential role in the formation of many kinds of mineral deposits and the generation of rock textures and mineral assemblages that may be diagnostic for extant or extinct life beyond Earth (5).A well-known example of a hyperthermophilic chemolithotrophic ecosystem is the pink filamentous streamers found at Octopus Spring in Yellowstone National Park (YNP), United States that were described by Brock in 1965 (3, 4). Similar streamer communities were first reported b...

Hopanes and steranes found in Archean rocks have been presented as key evidence supporting the early rise of oxygenic photosynthesis and eukaryotes, but the syngeneity of these hydrocarbon biomarkers is controversial. To resolve this debate, we performed a multilaboratory study of new cores from the Pilbara Craton, Australia, that were drilled and sampled using unprecedented hydrocarbon-clean protocols. Hopanes and steranes in rock extracts and hydropyrolysates from these new cores were typically at or below our femtogram detection limit, but when they were detectable, they had total hopane (<37.9 pg per gram of rock) and total sterane (<32.9 pg per gram of rock) concentrations comparable to those measured in blanks and negative control samples. In contrast, hopanes and steranes measured in the exteriors of conventionally drilled and curated rocks of stratigraphic equivalence reach concentrations of 389.5 pg per gram of rock and 1,039 pg per gram of rock, respectively. Polycyclic aromatic hydrocarbons and diamondoids, which exceed blank concentrations, exhibit individual concentrations up to 80 ng per gram of rock in rock extracts and up to 1,000 ng per gram of rock in hydropyrolysates from the ultraclean cores. These results demonstrate that previously studied Archean samples host mixtures of biomarker contaminants and indigenous overmature hydrocarbons. Therefore, existing lipid biomarker evidence cannot be invoked to support the emergence of oxygenic photosynthesis and eukaryotes by ∼2.7 billion years ago. Although suitable Proterozoic rocks exist, no currently known Archean strata lie within the appropriate thermal maturity window for syngenetic hydrocarbon biomarker preservation, so future exploration for Archean biomarkers should screen for rocks with milder thermal histories.oxygenic photosynthesis | eukaryotes | cyanobacteria | Great Oxidation Event | Pilbara

XMDS2 is a cross-platform, GPL-licensed, open source package for numerically integrating initial value problems that range from a single ordinary differential equation up to systems of coupled stochastic partial differential equations. The equations are described in a high-level XML-based script, and the package generates low-level optionally parallelised C++ code for the efficient solution of those equations. It combines the advantages of high-level simulations, namely fast and low-error development, with the speed, portability and scalability of hand-written code. XMDS2 is a complete redesign of the XMDS package, and features support for a much wider problem space while also producing faster code.

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