The serpentinite-hosted Lost City hydrothermal field is a remarkable submarine ecosystem in which geological, chemical, and biological processes are intimately interlinked. Reactions between seawater and upper mantle peridotite produce methane- and hydrogen-rich fluids, with temperatures ranging from <40 degrees to 90 degrees C at pH 9 to 11, and carbonate chimneys 30 to 60 meters tall. A low diversity of microorganisms related to methane-cycling Archaea thrive in the warm porous interiors of the edifices. Macrofaunal communities show a degree of species diversity at least as high as that of black smoker vent sites along the Mid-Atlantic Ridge, but they lack the high biomasses of chemosynthetic organisms that are typical of volcanically driven systems.

Abstract. The Curiosity rover discovered fine--grained sedimentary rocks, inferred to represent an ancient lake, preserve evidence of an environment that would have been suited to support a Martian biosphere founded on chemolithoautotrophy. This aqueous environment was characterized by neutral pH, low salinity, and variable redox states of both iron and sulfur species. C, H, O, S, N, and P were measured directly as key biogenic elements, and by inference N and P are assumed to have been available. The environment likely had a minimum duration of hundreds to tens of thousands of years. These results highlight the biological viability of fluvial--lacustrine environments in the post--Noachian history of Mars.

X-ray diffraction analysis of the Rocknest scoop sample is described in (23); similar analyses were performed for John Klein and Cumberland. John Klein and Cumberland were the first two drill samples collected by Curiosity. All scooped or drilled samples pass through the Collection and Handling for In situ Martian Rock Analysis (CHIMRA) sample collection and processing system (10). All powders for X-ray diffraction are processed through a 150-m sieve before delivering a portion to the CheMin inlet funnel.The sieved drill powders were placed into sample cells with 6 μm thick Mylar® windows. Mylar® contributes a minor, broad scattering signature in diffraction patterns that is generally "swamped" by diffraction from the loaded sample. In addition, an aluminized light shield also contributes "peaks" to the observed diffraction patterns. Only ~10 mm 3 of material is required to fill the active volume of the sample cell, which is a disc-shaped volume 8 mm in diameter and 175 m thick. A collimated ∼70 μm diameter X-ray beam illuminates the center of the sample cell. A piezoelectric vibration system on each cell pair shakes the material during analysis, causing grains in the cell to pass through the X-ray beam in random orientations.CheMin measures XRD and XRF data simultaneously using Co radiation in transmission geometry (11). The instrument operates in single-photon counting mode so that between each readout the majority of CCD pixels are struck by either a single X-ray photon or by no photons. In this way, the system can determine both the energy of the photons striking the CCD (XRF) and the two-dimensional (2-D) position of each photon (XRD). The energy and positional information of detected photons in each frame are summed over repeated 10-sec measurements into a "minor frame" of 30 min of data (180 frames). The 2-D distribution of Co K X-ray intensity represents the XRD pattern of the sample. Circumferential integration of these rings, corrected for arc length, produces a conventional 1-D XRD pattern. For conversion of the 2-D CCD pattern to a 1-D pattern we have used FilmScan © software from Materials Data, Inc.CheMin generally operates for only a few hours each night, when the CCD can be cooled to its lowest temperature, collecting as many minor frames as possible for the available analysis time, usually five to seven per night. XRD data were acquired over multiple nights for the John Klein and Cumberland drill samples to provide acceptable counting statistics. Total data collection times were 33.9 hr for John Klein and 20.2 hr for Cumberland. The data for individual minor frames and for each night's analysis were examined separately, and there was no evidence of any changes in instrumental parameters as a function of time over the duration of these analyses. Before sample delivery and analysis, the empty cell was analyzed to confirm that it was indeed empty before receiving the sample. The flight instrument was calibrated on the ground before flight using a quartz-beryl standard, and measurement of this st...

Oxygenation of the Earth's surface is increasingly thought to have occurred in two steps. The first step, which occurred approximately 2,300 million years (Myr) ago, involved a significant increase in atmospheric oxygen concentrations and oxygenation of the surface ocean. A further increase in atmospheric oxygen appears to have taken place during the late Neoproterozoic period ( approximately 800-542 Myr ago). This increase may have stimulated the evolution of macroscopic multicellular animals and the subsequent radiation of calcified invertebrates, and may have led to oxygenation of the deep ocean. However, the nature and timing of Neoproterozoic oxidation remain uncertain. Here we present high-resolution carbon isotope and sulphur isotope records from the Huqf Supergroup, Sultanate of Oman, that cover most of the Ediacaran period (approximately 635 to approximately 548 Myr ago). These records indicate that the ocean became increasingly oxygenated after the end of the Marinoan glaciation, and they allow us to identify three distinct stages of oxidation. When considered in the context of other records from this period, our data indicate that certain groups of eukaryotic organisms appeared and diversified during the second and third stages of oxygenation. The second stage corresponds with the Shuram excursion in the carbon isotope record and seems to have involved the oxidation of a large reservoir of organic carbon suspended in the deep ocean, indicating that this event may have had a key role in the evolution of eukaryotic organisms. Our data thus provide new insights into the oxygenation of the Ediacaran ocean and the stepwise restructuring of the carbon and sulphur cycles that occurred during this significant period of Earth's history.