Hydrogen (H₂) serves as a key point of interface between the geosphere and the biosphere and has likely done so since early in the history of Earth. Indeed, many of the most well accepted origin of life scenarios involve autotrophic microbial metabolisms that are fueled by redox reactions involving H₂, including the processes of acetogenesis and methanogenesis. Acetogens and methanogens use the iron sulfur (Fe-S) protein ferredoxin (Fd) to facilitate key electron transfers between H₂ and carbon reduction. However, the redox potential of H...

Two decades ago Fox and Woese demonstrated that the evolutionary comparison of 16/18S rRNA led to a trifucated unrooted tree that demonstrated that all living forms groups all living forms in one of three major phylogenetic lineages derived from a common ancestor. Bioinformatic analysis of completely sequenced cellular genomes from these three major kingdoms have been used to define the set of the most most conserved protein-encoding sequences to characterize the gene...

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Although biologists do not agree on what “life” is, given a few provisions, we understand the smallest unit is a cell bounded by a membrane across which is an electrochemical potential far from thermodynamic equilibrium. In the early part of the 20th century, Vladimir Vernadsky recognized that all cells exchange gases with the environment. These universal properties of life on Earth gave rise to a global scale electrical circuit, powered almost exclusively by light. The atmosphere and oceans are, in effect, planetary “wires” that connect the circuit from the...

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When we say a collection of matter has a form that is well-suited to a particular function, we are claiming implicitly that the particular arrangement of matter in question is much better at accomplishing some task than a random rearrangement would be.  In the biological context, we see many examples of form that supports function, and we very often seek to explain the exquisite non-randomness of structure as the result of successive rounds of self-replication, mutation, and selection.  One may also ask, however, what physical mechanisms may still give rise...

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The rovers Spirit and Opportunity touched down on Mars in January 2004 and have been conducting extensive observations with the Athena science payload. Together the two rovers have traversed more than 50 km. 

Spirit, located on the floor of Gusev crater, investigated basaltic plains, as well as older materials in the Columbia Hills. The rocks of the Columbia Hills are granular and have undergone significant alteration by water. They appear to be largely a mixture of altered impact ejecta and explosive volcanic materials. Spirit...

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Origin of Life studies primarily consist of two sets of inferences:  bottom-up, which infer plausible scenarios of abiogenesis given our understanding of planetary, geological, and chemical processes, and top-down, which reconstruct the evolutionary history of life for clues to its earliest states.  A discontinuity exists between these narratives, however, as deterministic physiochemical processes must give way to historic evolutionary processes before the common ancestry of any of the genetic lineages upon which top-down approaches rely.  This...

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I will describe various aspects of stellar activity that control the environment of exoplanets, produce photochemical reactions in their atmospheres, and drive mass loss. The fundamental drivers of stellar active phenomena are strong magnetic fields for which field strengths can be measured by Zeeman broadening of absorption lines in stellar spectra, and the large scale magnetic geometry and properties that can be measured with Zeeman Doppler imaging techniques. Magnetic heating processes produce warm chromospheres and hot coronae. ...

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The search for organic material and biosignatures in our solar system is a highly complex endeavor. For life to develop, chemical raw materials are necessary, hence space missions that investigate the composition of comets and asteroids and in particular their organic content provide major opportunities to determine the prebiotic reservoirs available to the early Earth and Mars. The comet rendezvous mission Rosetta was the first spacecraft to land on a comet and thus sampling material from a cometary nucleus. Rosetta monitored the evolution of comet 67P/...

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The overwhelmingly homochiral nature of life has left a puzzle as to whether mirror-image biological systems based on a chirally inverted version of molecular machinery could also have existed. We show that two processes in the central dogma of molecular biology, the template-directed polymerization of DNA and transcription into RNA, can be catalyzed by a chemically synthesized D-amino acid polymerase on an L-DNA template. The establishment of such molecular systems with an opposite handedness is a small step towards chemically synthesizing an alternative...

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Minerals, textures and shapes of sedimentary rocks may record metabolisms and environmental conditions that were present before the rise of atmospheric oxygen. For example, dolomite does not preserve fine microbial textures in modern seawater, but it commonly did so in the past. Furthermore, manganese oxides are only known to form in the presence of oxygen, so these minerals are used as proxies for the past presence of oxygen or oxygen-producing organisms. To better interpret the records of these minerals, we grew anoxygenic benthic photosynthetic microbial...

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Synthetic biology – the design and construction of new biological parts and systems and the ...

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The RNA World hypothesis, which posits that RNA existed before the advent of DNA and proteins, remains a popular and influential hypothesis. However, despite decades of effort, origins of life researchers are still lacking a plausible prebiotic synthesis for RNA. Persistent challenges include nucleobase selection, nucleoside bond formation, and nucleotide polymerization. We are investigating the possibility that RNA was preceded by a polymer that would have assembled more easily than RNA (i.e., pre-RNA), being comprised of different nucleobases and, perhaps, a different...

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This talk will discuss the results presented in our recent paper (Science 351, p.1414 and online aad6253). Recent work to analyze the minimal cell, and plans for further analysis will also be discussed. We used whole-genome design and complete chemical synthesis to minimize the 1079-kilobase pair synthetic genome of Mycoplasma mycoides JCVI-sym.o. An initial design, based on collective knowledge of molecular biology combined with limited transposon mutagenesis data, failed to produce a viable cell. Improved transposon mutagenesis methods revealed...