title: Follow the Carbon: Isotopic Labeling Studies of Early Earth Aerosol.
abstract: Despite the faint young Sun, early Earth might have been kept warm by an atmosphere containing the greenhouse gases CH4and CO2in mixing ratios higher than those found on Earth today. Laboratory and modeling studies suggest that an atmosphere containing these trace gases could lead to the formation of organic aerosol haze due to UV photochemistry. Chemical mechanisms proposed to explain haze formation rely on CH4as the source of carbon and treat CO2as a source of oxygen only, but this has not previously been verified experimentally. In the present work, we use isotopically labeled precursor gases and unit-mass resolution (UMR) and high-resolution (HR) aerosol mass spectrometry to examine the sources of carbon and oxygen to photochemical aerosol formed in a CH4/CO2/N2atmosphere. UMR results suggest that CH4contributes 70-100% of carbon in the aerosol, while HR results constrain the value from 94% to 100%. We also confirm that CO2contributes approximately 10% of the total mass to the aerosol as oxygen. These results have implications for the geochemical interpretations of inclusions found in Archean rocks on Earth and for the astrobiological potential of other planetary atmospheres. Key Words: Atmosphere-Early Earth-Planetary atmospheres-Carbon dioxide-Methane. Astrobiology 16, 822-830.
authors.affiliation: Department of Chemistry and Biochemistry, and Cooperative Institute for Research in Environmental Sciences, University of Colorado , Boulder, Colorado.
authors.forename: Raea K
authors.initials: RK
authors.lastname: Hicks
authors.affiliation: Department of Chemistry and Biochemistry, and Cooperative Institute for Research in Environmental Sciences, University of Colorado , Boulder, Colorado.
authors.forename: Douglas A
authors.initials: DA
authors.lastname: Day
authors.affiliation: Department of Chemistry and Biochemistry, and Cooperative Institute for Research in Environmental Sciences, University of Colorado , Boulder, Colorado.
authors.forename: Jose L
authors.initials: JL
authors.lastname: Jimenez
authors.affiliation: Department of Chemistry and Biochemistry, and Cooperative Institute for Research in Environmental Sciences, University of Colorado , Boulder, Colorado.
authors.forename: Margaret A
authors.initials: MA
authors.lastname: Tolbert
mesh_terms: D000336:Aerosols / Q000032:analysis*; D002244:Carbon / Q000032:analysis*; D002247:Carbon Isotopes; D018534:Earth, Planet; D007553:Isotope Labeling / Q000379:methods*; D013058:Mass Spectrometry
chemical_list: D000336:Aerosols; D002247:Carbon Isotopes; D002244:Carbon