[M-IS07] 水惑星学

[MIS07-P17] New sulfur isotopes 1-D photochemical model for revealing early earth's atmosphere

*遠藤 美朗^1,2、Claire Mark²、Chester Harman^2,3、Laura Crick² (1.東京工業大学大学院、2.University of St Andrews、3.NASA Ames Research Center)

キーワード：初期地球大気、硫黄同位体

Constraining the atmospheric composition of planets is essential to understanding habitability. However, the chemical composition of the early Earth's atmosphere is poorly understood. Here, mass-independent fractionation of sulfur isotopes (MIF-S) in pre-2.4 Ga sedimentary rocks provide a hint of atmospheric composition at that time. For the early Earth, it is believed that partial pressure of O₂ was very low and atmosphere was reducing. Recently, our sulfur dioxide (SO₂) photochemical experiments under carbon monoxide (CO) atmosphere reproduced the Δ³⁶S/Δ³³S slope from the Archean (~−1), which is the most basic character of Archean MIF-S (Endo et al. 2016). Moreover, it was found that the MIF-S trend depends on total pressure, indicating that MIF-S is sensitive to absorption spectral shape of SO₂ via SO₂’s own UV absorption (Endo et al. 2019). We synthesized SO₂ isotopologues absorption spectra which reproduce the MIF-S of photochemical experiments (Endo et al. 2019). Therefore, we can predict MIF-S produced in various atmospheric compositions using the SO₂ isotopologues absorption spectra and irradiative UV spectra, and the resulting MIF-S depends on altitude. Here, we develop a 1-D (vertical) photochemical model including 4 sulfur isotopes (³²S, ³³S, ³⁴S, and ³⁶S) and very high resolution SO₂ absorption spectra (~0.0004 nm). This new model is based on previous models including sulfur isotopes and low wavelength resolution SO₂ absorption spectra (Claire et al. 2014; Izon et al. 2017). We will present preliminary results and discuss the meaning of MIF-S in Early Earth rocks and modern atmospheric sulfates, if possible, Martian meteorites.