Earth: Atmospheric Evolution of a Habitable Planet

Abstract

Our present-day atmosphere is often used as an analog for potentially habitable exoplanets, but Earth's atmosphere has changed dramatically throughout its 4.5-billion-year history. For example, molecular oxygen is abundant in the atmosphere today but was absent on the early Earth. Meanwhile, the physical and chemical evolution of Earth's atmosphere has also resulted in major swings in surface temperature, at times resulting in extreme glaciation or warm greenhouse climates. Despite this dynamic and occasionally dramatic history, the Earth has been persistently habitable-and, in fact, inhabited-for roughly 4 billion years. Understanding Earth's momentous changes and its enduring habitability is essential as a guide to the diversity of habitable planetary environments that may exist beyond our solar system and for ultimately recognizing spectroscopic fingerprints of life elsewhere in the Universe.Here, we review long-term trends in the composition of Earth's atmosphere as it relates to both planetary habitability and inhabitation. We focus on gases that may serve as habitability markers (CO2, N2) or biosignatures (CH4, O2), especially as related to the redox evolution of the atmosphere and the coupled evolution of Earth's climate system. We emphasize that in the search for Earth-like planets we must be mindful that the example provided by the modern atmosphere merely represents a single snapshot of Earth's long-term evolution. In exploring the many former states of our own planet, we emphasize Earth's atmospheric evolution during the Archean, Proterozoic, and Phanerozoic eons, but we conclude with a brief discussion of potential atmospheric trajectories into the distant future, many millions to billions of years from now. All of these 'Alternative Earth' scenarios provide insight to the potential diversity of Earth-like, habitable, and inhabited worlds.

Precambrian Paleobiology: Precedents, Progress, and Prospects

“…This is not to imply, however, that Earth's atmosphere became "fully oxygenated" at 2.3 Ga. Indeed, current estimates indicate that permanent oxygenation was not attained until ∼2.2 Ga, 100 Ma later (Poulton et al, 2021), and even then remained at low concentrations, far below current atmospheric levels, for the following billion years or more (Olson et al, 2018).…”

Biogeochemical and physical controls on methane fluxes from two ferruginous meromictic lakes

“…In the absence of O 2 , CH 4 is estimated to have reached a maximum of ~50× pre-industrial atmospheric levels (ca. 700 ppb; Etheridge, Steele, Francey, & Langenfelds, 1998) assuming pCO 2 near upper paleosol limits (Olson et al, 2018). After the "Great Oxidation Event" (ca.…”

“…The focus on CH 4 extends out of the water column as it is one of the main gases thought to have regulated early Earth climate in the Archean. Paleoatmospheric modeling suggests that CH 4 was an important greenhouse gas, in addition to CO 2 , that warmed Earth during the lower solar luminosity experienced in the Archean and Proterozoic Eons (see Olson, Schwieterman, Reinhard, & Lyons, and references therein). As soon as methanogenesis evolved ~3.5 Ga (Ueno, Yamada, Yoshida, Maruyama, & Isozaki, ; Wolfe & Fournier, ), CH 4 could begin to accumulate in the reduced Archean atmosphere.…”

Thermal and Oxygen Flight Sensitivity in Ageing Drosophila melanogaster Flies: Links to Rapamycin-Induced Cell Size Changes

“…At present, the Earth’s atmosphere contains 21% O 2 and the global average surface temperature is ca. 15 °C [ 1 ], but on a geological timescale, these parameters have been changing dramatically, driving ecological and evolutionary transitions in life. In ectotherms, global atmospheric processes are often indicated to be an important selective driver in the evolution of body size [ 2 , 3 , 4 , 5 ], which is the primary life history trait with strong correspondence to fitness [ 6 , 7 , 8 ].…”