Influence of Biomass Emissions on Habitability, Biosignatures, and Detectability in Earth-like Atmospheres

Abstract

We investigate atmospheric responses of modeled hypothetical Earth-like planets in the habitable zone of the M-dwarf AD Leonis to reduced oxygen (O2), removed biomass ("dead" Earth), varying carbon dioxide (CO2) and surface relative humidity (sRH). Results suggest large O2 differences between the reduced O2 and "dead" scenarios in the lower but not the upper atmosphere. Ozone (O3) and nitrous oxide (N2O) also show this behavior. Methane depends on hydroxyl (OH), its main sink. Abiotic production of N2O occurs in the upper layers.Chloromethane (CH3Cl) decreases everywhere on decreasing biomass. Changing CO2 (from x1 to x100 present atmospheric level (PAL)) and surface relative humidity (sRH) (from 0.1% to 100%) does not influence CH3Cl as much as lowering biomass.Therefore, CH3Cl can be considered a good biosignature. Changing sRH and CO2 has a greater influence on temperature than O2 and biomass alone. Changing the biomass produces ~6 kilometer (km) in effective height (H) in transmission compared with changing CO2 and sRH (~25km). In transmission O2 is discernible at 0.76 µm for >0.1 PAL. The O3 9.6 µm band was weak for the low O2 runs and difficult to discern from "dead" Earth", however O3 at 0.3 µm could serve as an indicator to distinguish between reduced O2 and "dead" Earth. Spectral features of N2O and CH3Cl corresponded to some km H. CH4 could be detectable tens of

Variations in climate habitability parameters and their effect on Earth's biosphere during the Phanerozoic Eon

“…The amount of O 2 characteristic of a thriving terrestrial floral biosphere can be inferred from the planetary spectral features at 0.69, 0.76, 0.77 and 1.27 μm 58 . Its atmospheric proxy O 3 can also be used, as it exhibits more dominant features compared to O 2 at ~ 0.25, 0.4–0.85 and 9.6 μm 59 . CO 2 levels, moreover, can be inferred from the dominant 4.3 and 15 μm features in the (exo)planetary spectra.…”