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.

arXiv comment34 pages, 4 figures, 4 tables. Review chapter to appear in Handbook of Exoplanets

References in corpus (15)

• Habitable Zones Around Main-Sequence Stars: New Estimates
• The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth
• Abiotic oxygen-dominated atmospheres on terrestrial habitable zone planets
• Nitrogen Isotopic Composition and Density of the Archean Atmosphere
• The Nitrogen Budget of Earth
• Exploring the faint young Sun problem and the possible climates of the Archean Earth with a 3-D GCM
• False negatives for remote life detection on ocean-bearing planets: Lessons from the early Earth
• Detecting and Constraining N${}_2$ Abundances in Planetary Atmospheres Using Collisional Pairs
• Organic Haze as a Biosignature in Anoxic Earth-like Atmospheres
• Faint young Sun paradox remains
• Atmospheric nitrogen evolution on Earth and Venus
• Swansong Biospheres: Refuges for life and novel microbial biospheres on terrestrial planets near the end of their habitable lifetimes
• Modeling pN2 through Geological Time: Implications for Planetary Climates and Atmospheric Biosignatures
• Clouds and the Faint Young Sun Paradox
• Evolution of Earth-like extrasolar planetary atmospheres: Assessing the atmospheres and biospheres of early Earth analog planets with a coupled atmosphere biogeochemical model

Cited by in corpus (3)

• Large Interferometer For Exoplanets (LIFE): V. Diagnostic potential of a mid-infrared space-interferometer for studying Earth analogs
• Revisiting the Biological Ramifications of Variations in Earth's Magnetic Field
• Population-level Hypothesis Testing with Rocky Planet Emission Data: A Tentative Trend in the Brightness Temperatures of M-Earths