The Role of Tectonic Luck in Long-Term Habitability of Abiotic Earth-like Planets

TL;DR

This study models the long-term climate stability of Earth-like planets, highlighting the importance of mineral resupply mechanisms beyond tectonic uplift for maintaining habitability over geological timescales.

Contribution

It introduces a quasi-2D climate model demonstrating that tectonic uplift alone cannot sustain habitable conditions, emphasizing the need for additional mineral resupply processes.

Findings

Tectonic uplift alone leads to uninhabitable or unstable climates.

Mineral resupply mechanisms like wind and erosion are crucial for climate stability.

Variable outgassing and stellar luminosity destabilize planetary climates.

Abstract

Carbonate-silicate weathering feedback is thought to stabilize Earth's climate on geologic timescales. If climate warms, faster mineral dissolution and increased rainfall speed up weathering, increasing CO2 drawdown and opposing the initial warming. Limits to where this feedback might operate on terrestrial exoplanets with N2-O2-CO2-H2O atmospheres are used to define the 'habitable zone'-the range of orbits around a star where liquid water can be stable on a planet's surface. However, the impacts on long-term habitability of randomly varying volcanic outgassing, tectonic collisions, and tectonic parameters (e.g., number of continental plates, size of plates, plate velocity) remain poorly understood. In this work, we present an idealized and broadly-applicable quasi-2D model of the long-term climate stability of abiotic Earth-twins. The model tracks atmospheric CO2 as 'disks' collide, promoting uplift and supplying new weatherable minerals through erosion. Without resupply, soils become less weatherable and the feedback's strength wanes, making a planet susceptible to catastrophic warming events or hard snowballs where the surface becomes frozen over. We find that tectonic uplift spurred by continental collisions cannot be the sole supplier of weatherable minerals within our model framework, as such climates either become uninhabitably hot (for complex life) as soils become leached of weatherable minerals or experience extreme swings in temperature over short timescales. This conclusion is strengthened when taking into account the destabilizing effects of outgassing variability and increasing stellar luminosity. In addition to frequent collisions, other resupply mechanisms for weatherable minerals, such as wind-driven dust transport, glacial erosion, and/or seafloor weathering, are likely required for long-term stability on Earth-like terrestrial exoplanets.