[M-IS08] Astrobiology

[MIS08-P07] The Archean Underwater Light Environment: Implications for Habitability of Earth's Surface and Potential Biosignatures

*Chihiro Arai¹, Yuka Fujii², Kumiko Ito-Miwa¹, Yuri I. Fujii³, Satomi Kanno¹, Taro Matsuo^1,4 (1.Nagoya University, 2.National Astronomical Observatory of Japan, 3.Kyoto University, 4.Osaka Universisty)

In the Archean era, oxygenic photosynthesis dramatically transformed the water environment from a reducing to an oxidizing state, leading to the formation of large-scale banded iron formations (BIF) as dissolved Fe(II) was oxidized into iron hydroxide. The oxidation of the oceans may have triggered a significant, global-scale change in the underwater light environment, driven by the unique optical properties of the precipitated iron hydroxide. While iron hydroxide absorbed ultraviolet light, which allowed the biosphere to expand to the ocean surface, it might have also absorbed blue light, resulting in a green-light environment.
Understanding the light environment in the Archean oceans will not only provide insights into the habitability of the Earth's surface in the Archean era but also potentially offer a new approach to detecting signs of life on distant planets. In this study, we simulate the underwater light transmission and reflectance of the Archean oceans by combining measured absorption coefficients from iron hydroxide samples with scattering coefficients calculated using Mie theory. We will also discuss how the concentration of iron hydroxide could affect the color of the sea as a potential biosignature.