2007 Annual Science Report
Pennsylvania State University Reporting | JUL 2006 – JUN 2007
Modeling Early Atmospheric Composition and Climate (Kasting)
My students and I, along with my collaborator Dave Pollard, have made progress on several fronts:
1) Dave Pollard and I published a response to a comment by Steve Warren and Richard Brandt on our “thin-ice” model of Neoproterozoic Snowball Earth (see publications listed below). In the original paper, Dave and I argued that the equatorward flow of sea glaciers, discussed by Goodman and Pierrehumbert (JGR, 2003) does not necessarily preclude the existence of thin (~1-m) ice in the tropics. Warren and Brandt then argued that because the optical properties of the ice had been misconstrued by us, thin ice was precluded. We looked at things again and found that thin ice is allowed under a variety of circumstances. Read the papers to find out the details.
2) We have made more progress in understanding climate during the Archean Era. In Kasting and Howard (2006), we discuss the possible significance of the low Δ33S values seen in sulfides deposited between about 2.8 Ga and 3.2 Ga. We suggest that they are linked to the development of a thick organic haze that inhibited SO2 photolysis. This is an alternative to the idea we published previously (Kasting and Ono, 2006) and also to the Ohmoto et al. “yo-yo atmosphere” hypothesis. A more detailed paper, first authored by my student Shawn Goldman, has been submitted to EPSL and is currently under revision.
3) In Kasting et al., EPSL (2006), we proposed a new explanation for the decrease in the δ18O values of sedimentary cherts and carbonates in the distant past. We suggested that seawater δ18O increased with time as a consequence of changing tectonic styles and their effect on water-rock interactions within the midocean ridge hydrothermal vents. If correct, this implies that low δ18O values of ancient sedimentary rocks cannot be taken as evidence for a hot Archean climate. In a related twist, our mechanism can also explain the long-term trend in silicon isotopes observed by Robert and Chaussidon (2006). See the comment in Nature by Shields and Kasting (2007).
4) My work as co-chair of NASA’s TPF-C Science and Technology Definition team wrapped up. This resulted in the publication of a technical report (Levine et al., 2006) on the Flight Baseline 1 TPF-C mission design. My own contribution was primarily to help establish the science requirements for the mission.
5) I supervised Feng Tian’s NAI postdoc work on hydrodynamic escape of gases from planetary atmospheres. A first paper has been submitted to Icarus (Tian et al., submitted). The paper gives the details of the upper atmosphere model and shows its application to Earth’s present atmosphere under a variety of solar EUV heating rates.
6) In collaborations with French astronomers, especially Frank Selsis, I have contributed to a paper on hypothetical ocean planets (Selsis et al., Icarus, submitted) and on the habitability, or lack thereof, of Gliese 581c (Selsis et al., Astron. & Astroph
PROJECT INVESTIGATORS:James Kasting
PROJECT MEMBERS:Dave Pollard
RELATED OBJECTIVES:Objective 4.1
Earth's early biosphere
Biosignatures to be sought in nearby planetary systems