Linda Christine Kah

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Progressive oxygenation of the Earth's early biosphere is thought to have resulted in increased sulphide oxidation during continental weathering, leading to a corresponding increase in marine sulphate concentration. Accurate reconstruction of marine sulphate reservoir size is therefore important for interpreting the oxygenation history of early Earth(More)
The environmental expression of sulfur compound disproportionation has been placed between 640 and 1050 million years ago (Ma) and linked to increases in atmospheric oxygen. These arguments have their basis in temporal changes in the magnitude of 34S/32S fractionations between sulfate and sulfide. Here, we present a Proterozoic seawater sulfate isotope(More)
The Curiosity rover discovered fine-grained sedimentary rocks, which are inferred to represent an ancient lake and 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(More)
Observations by the Mars Science Laboratory Mast Camera (Mastcam) in Gale crater reveal isolated outcrops of cemented pebbles (2 to 40 millimeters in diameter) and sand grains with textures typical of fluvial sedimentary conglomerates. Rounded pebbles in the conglomerates indicate substantial fluvial abrasion. ChemCam emission spectra at one outcrop show a(More)
The Rocknest aeolian deposit is similar to aeolian features analyzed by the Mars Exploration Rovers (MERs) Spirit and Opportunity. The fraction of sand <150 micrometers in size contains ~55% crystalline material consistent with a basaltic heritage and ~45% x-ray amorphous material. The amorphous component of Rocknest is iron-rich and silicon-poor and is the(More)
The landforms of northern Gale crater on Mars expose thick sequences of sedimentary rocks. Based on images obtained by the Curiosity rover, we interpret these outcrops as evidence for past fluvial, deltaic, and lacustrine environments. Degradation of the crater wall and rim probably supplied these sediments, which advanced inward from the wall, infilling(More)
Introduction: The Mars Science Laboratory (MSL) is NASA's next rover mission to Mars, planned for launch in 2011. Four years ago, Edgett et al. [1] described the science objectives of the MSL Mars Hand Lens Imager (MAHLI) investigation. The instrument has now been built and the camera head (Fig. 1) was delivered in October 2008 to Caltech's Jet Propulsion(More)
Stable isotope ratios of H, C, and O are powerful indicators of a wide variety of planetary geophysical processes, and for Mars they reveal the record of loss of its atmosphere and subsequent interactions with its surface such as carbonate formation. We report in situ measurements of the isotopic ratios of D/H and (18)O/(16)O in water and (13)C/(12)C,(More)
Introduction: The Mars Descent Imager (MARDI) is a fixed-focus color camera mounted on the forward port side of the Mars Science Laboratory (MSL) rover. The optic axis points in the +Z direction (towards the ground). The camera can obtain 1600 x 1200 pixel images at a rate of 4.5 frames per second throughout the period between heatshield separation and(More)
and classified as cryptomicrobial boundstones. Under close re-examination, these rocks reveal mesoscopic and microscopic fabrics which are indeed thrombolitic when considered in the context of the recent tripartate microbialite classification scheme developed by Kennard and James (1986) and Kennard (1989). Thrombolitic fabrics from the Rocknest Formation(More)