1. Rapid oxygenation of Earth's atmosphere 2.33 billion years ago.

    Science advances 2(5):e1600134 (2016) PMID 27386544 PMCID PMC4928975

    Molecular oxygen (O2) is, and has been, a primary driver of biological evolution and shapes the contemporary landscape of Earth's biogeochemical cycles. Although "whiffs" of oxygen have been documented in the Archean atmosphere, substantial O2 did not accumulate irreversibly until the Early Pale...
  2. Methane cycling. Nonequilibrium clumped isotope signals in microbial methane.

    Science 348(6233):428 (2015) PMID 25745067

    Methane is a key component in the global carbon cycle, with a wide range of anthropogenic and natural sources. Although isotopic compositions of methane have traditionally aided source identification, the abundance of its multiply substituted "clumped" isotopologues (for example, (13)CH3D) has r...
  3. Millimeter-wave optical double resonance schemes for rapid assignment of perturbed spectra, with applications to the C̃ (1)B(2) state of SO2.

    Journal of Chemical Physics 142(14):144201 (2015) PMID 25877571

    Millimeter-wave detected, millimeter-wave optical double resonance (mmODR) spectroscopy is a powerful tool for the analysis of dense, complicated regions in the optical spectra of small molecules. The availability of cavity-free microwave and millimeter wave spectrometers with frequency-agile ge...
  4. Decline in oceanic sulfate levels during the early Mesoproterozoic

    Precambrian Research 258:36 (2015)

    • Multiple sulfur isotopes were analyzed for early Mesoproterozoic CAS and pyrite. • Paired CAS and pyrite δ34S suggest low sulfur isotope fractionation (<10‰). ...
  5. Predictive isotope model connects microbes in culture and nature.

    PNAS 111(51):18102 (2014) PMID 25480549 PMCID PMC4280631

  6. Measurement of a doubly substituted methane isotopologue, ¹³CH₃D, by tunable infrared laser direct absorption spectroscopy.

    Analytical chemistry 86(13):6487 (2014) PMID 24895840

    Methane is an important energy resource and significant long-lived greenhouse gas. Carbon and hydrogen isotope ratios have been used to better constrain the sources of methane but interpretations based on these two parameters alone can often be inconclusive. The precise measurement of a doubly s...
  7. Consumption of atmospheric hydrogen during the life cycle of soil-dwelling actinobacteria.

    Environmental Microbiology Reports 6(3):226 (2014) PMID 24983527

    Microbe-mediated soil uptake is the largest and most uncertain variable in the budget of atmospheric hydrogen (H2 ). The diversity and ecophysiological role of soil microorganisms that can consume low atmospheric abundances of H2 with high-affinity [NiFe]-hydrogenases is unknown. We expanded the...
  8. Development of a spectroscopic technique for continuous online monitoring of oxygen and site-specific nitrogen isotopic composition of atmospheric nitrous oxide.

    Analytical chemistry 86(3):1726 (2014) PMID 24328290

    Nitrous oxide is an important greenhouse gas and ozone-depleting-substance. Its sources are diffuse and poorly characterized, complicating efforts to understand anthropogenic impacts and develop mitigation policies. Online, spectroscopic analysis of N2O isotopic composition can provide continuou...
  9. Multiple sulfur isotope signatures of sulfite and thiosulfate reduction by the model dissimilatory sulfate-reducer, Desulfovibrio alaskensis str. G20.

    Frontiers in Microbiology 5:591 (2014) PMID 25505449 PMCID PMC4243691

    Dissimilatory sulfate reduction serves as a key metabolic carbon remineralization process in anoxic marine environments. Sulfate reducing microorganisms can impart a wide range in mass-dependent sulfur isotopic fractionation. As such, the presence and relative activity of these organisms is iden...
  10. Vibronic origin of sulfur mass-independent isotope effect in photoexcitation of SO2 and the implications to the early earth's atmosphere.

    PNAS 110(44):17697 (2013) PMID 23836655 PMCID PMC3816475

    Signatures of mass-independent isotope fractionation (MIF) are found in the oxygen ((16)O,(17)O,(18)O) and sulfur ((32)S, (33)S, (34)S, (36)S) isotope systems and serve as important tracers of past and present atmospheric processes. These unique isotope signatures signify the breakdown of the tr...
  11. Fully automated, high-precision instrumentation for the isotopic analysis of tropospheric N2O using continuous flow isotope ratio mass spectrometry.

    Rapid Communications in Mass Spectrometry 27(15):1723 (2013) PMID 23821566

    Measurements of the isotopic composition of nitrous oxide in the troposphere have the potential to bring new information about the uncertain N2O budget, which mole fraction data alone have not been able to resolve. Characterizing the expected subtle variations in tropospheric N2O isotopic compos...
  12. Manganese-oxidizing photosynthesis before the rise of cyanobacteria.

    PNAS 110(28):11238 (2013) PMID 23798417 PMCID PMC3710856

    The emergence of oxygen-producing (oxygenic) photosynthesis fundamentally transformed our planet; however, the processes that led to the evolution of biological water splitting have remained largely unknown. To illuminate this history, we examined the behavior of the ancient Mn cycle using newly...
  13. Evidence for microbial carbon and sulfur cycling in deeply buried ridge flank basalt.

    Science 339(6125):1305 (2013) PMID 23493710

    Sediment-covered basalt on the flanks of mid-ocean ridges constitutes most of Earth's oceanic crust, but the composition and metabolic function of its microbial ecosystem are largely unknown. By drilling into 3.5-million-year-old subseafloor basalt, we demonstrated the presence of methane- and s...
  14. High-precision measurements of (33)S and (34)S fractionation during SO2 oxidation reveal causes of seasonality in SO2 and sulfate isotopic composition.

    Environmental Science & Technology 47(21):12174 (2013) PMID 24079753

    This study presents high-precision isotope ratio-mass spectrometric measurements of isotopic fractionation during oxidation of SO2 by OH radicals in the gas phase and H2O2 and transition metal ion catalysis (TMI-catalysis) in the aqueous phase. Although temperature dependence of fractionation fa...
  15. Fractionation of sulfur isotopes by Desulfovibrio vulgaris mutants lacking hydrogenases or type I tetraheme cytochrome c 3.

    Frontiers in Microbiology 4:171 (2013) PMID 23805134 PMCID PMC3691511

    The sulfur isotope effect produced by sulfate reducing microbes is commonly used to trace biogeochemical cycles of sulfur and carbon in aquatic and sedimentary environments. To test the contribution of intracellular coupling between carbon and sulfur metabolisms to the overall magnitude of the s...
  16. Effects of iron and nitrogen limitation on sulfur isotope fractionation during microbial sulfate reduction.

    Applied and Environmental Microbiology 78(23):8368 (2012) PMID 23001667 PMCID PMC3497358

    Sulfate-reducing microbes utilize sulfate as an electron acceptor and produce sulfide that is depleted in heavy isotopes of sulfur relative to sulfate. Thus, the distribution of sulfur isotopes in sediments can trace microbial sulfate reduction (MSR), and it also has the potential to reflect the...
  17. Excitation band dependence of sulfur isotope mass-independent fractionation during photochemistry of sulfur dioxide using broadband light sources

    Geochimica et Cosmochimica Acta 94:238 (2012)

    Ultraviolet photolysis of sulfur dioxide (SO2) is hypothesized to be the source of the sulfur isotope mass-independent fractionation (S-MIF) observed in Archean sulfate and sulfide minerals and modern stratospheric sulfate aerosols. A series of photochemical experiments were performed ...
  18. Sulfur-33 constraints on the origin of secondary pyrite in altered oceanic basement

    Geochimica et Cosmochimica Acta 87:323 (2012)

    Low temperature alteration of oceanic basement rocks is characterized by net gain of sulfur, which commonly yields low δ34S values, suggesting involvement of microbial sulfate reduction. In order to test whether secondary sulfide minerals are consistent with a biogenic source, we apply...
  19. Sulfur mass-independent fractionation in liquid phase chemistry: UV photolysis of phenacylphenylsulfone as a case study

    Geochimica et Cosmochimica Acta 85:160 (2012)

    The sulfur isotope mass-independent fractionation (S-MIF) represents a distinct geochemical signature commonly observed in Archean rocks. Although S-MIF is generally thought to be exclusive to gas phase chemistry, several studies have suggested that liquid phase or heterogeneous chemis...
  20. Large sulfur isotope fractionation does not require disproportionation.

    Science 333(6038):74 (2011) PMID 21719675

    The composition of sulfur isotopes in sedimentary sulfides and sulfates traces the sulfur cycle throughout Earth's history. In particular, depletions of sulfur-34 ((34)S) in sulfide relative to sulfate exceeding 47 per mil (‰) often serve as a proxy for the disproportionation of intermediate sul...