title: Haze aerosols in the atmosphere of early Earth: manna from heaven.
abstract: An organic haze layer in the upper atmosphere of Titan plays a crucial role in the atmospheric composition and climate of that moon. Such a haze layer may also have existed on the early Earth, providing an ultraviolet shield for greenhouse gases needed to warm the planet enough for life to arise and evolve. Despite the implications of such a haze layer, little is known about the organic material produced under early Earth conditions when both CO(2) and CH(4) may have been abundant in the atmosphere. For the first time, we experimentally demonstrate that organic haze can be generated in different CH(4)/CO(2) ratios. Here, we show that haze aerosols are able to form at CH(4) mixing ratios of 1,000 ppmv, a level likely to be present on early Earth. In addition, we find that organic hazes will form at C/O ratios as low as 0.6, which is lower than the predicted value of unity. We also show that as the C/O ratio decreases, the organic particles produced are more oxidized and contain biologically labile compounds. After life arose, the haze may thus have provided food for biota.
authors.affiliation: Department of Chemistry and Biochemistry and Cooperative Institute for Research in Environmental Sciences, University of Colorado at Boulder, Boulder, Colorado 80309-0216, USA.
authors.forename: Melissa G
authors.initials: MG
authors.lastname: Trainer
authors.forename: Alexander A
authors.initials: AA
authors.lastname: Pavlov
authors.forename: Daniel B
authors.initials: DB
authors.lastname: Curtis
authors.forename: Christopher P
authors.initials: CP
authors.lastname: McKay
authors.forename: Douglas R
authors.initials: DR
authors.lastname: Worsnop
authors.forename: Alice E
authors.initials: AE
authors.lastname: Delia
authors.forename: Darin W
authors.initials: DW
authors.lastname: Toohey
authors.forename: Owen B
authors.initials: OB
authors.lastname: Toon
authors.forename: Margaret A
authors.initials: MA
authors.lastname: Tolbert
mesh_terms: D000336:Aerosols; D001272:Atmosphere / Q000737:chemistry*; D002245:Carbon Dioxide; D018534:Earth, Planet; D018559:Exobiology; D013058:Mass Spectrometry; D008697:Methane; D019021:Natural History; D009584:Nitrogen; D018539:Saturn
chemical_list: D000336:Aerosols; D002245:Carbon Dioxide; D009584:Nitrogen; D008697:Methane