Exploring Archean Climate Through Three Case Studies

Abstract

The Archean Eon (4.0–2.5 Ga) spans one third of Earth’s history and includes the emergence of life. It is also the earliest period with a relatively well-preserved geological record, which provides key insights into early environmental conditions. Although Archean climate is poorly constrained due to uncertainties in proxy interpretation, it is clear that it was fundamentally different to Earth’s present climate while remaining hospitable to life. This thesis investigates Archean climate through three case studies, each examining sensitivity to a major uncertain parameter using climate models of appropriate complexity.
First, the sensitivity of atmospheric circulation and surface temperature distribution to the presence of continents is explored using an idealised general circulation model. A range of continental configurations are introduced to an Archean aquaplanet, and both the large-scale atmospheric circulation and zonal-mean surface temperature distribution are shown to reorganise in response to changes in the surface energy budget. Variations in albedo and surface moisture availability influence outgoing radiative fluxes, while continental distribution and land-sea albedo contrast determine which process dominates. Second, climate sensitivity near the threshold of global glaciation is assessed with respect to tidal dissipation and geothermal heat using a dedicated tidal model and an Earth system model of intermediate complexity. Tidal dissipation enhances vertical mixing and, together with a plausible geothermal heat flux, buffers Snowball bifurcation toward a lower critical CO2 threshold, potentially contributing to the resolution of the faint young Sun problem. For the topography used to represent early Earth here, the threshold decreases by 4.2%. Finally, the feasibility of a hot Archean surface climate is tested using a single-column model informed by geological constraints of the atmosphere. Surface temperatures >70°C in the early Archean have been speculated for decades but remain controversial. The atmospheres modelled here sample the full published range of Archean CO2, CH4, and surface pressure constraints but none of the simulations approach 70°C. This challenges the hot Archean hypothesis and provides insight into the maintenance of a temperate climate under extreme atmospheres.
Collectively, results support a broadly temperate Archean climate despite reduced solar luminosity, while remaining regionally dynamic and sensitive to atmospheric, oceanic, and geographic controls. As Archean Earth represents a young and habitable terrestrial planet, the results in this thesis also inform the broader problem of exoplanet habitability.

Date of Award	1 Jun 2026
Original language	English
Awarding Institution	Bangor University
Sponsors	Leverhulme Trust
Supervisor	Mattias Green (Supervisor), Stephen Thomson (Supervisor) & Nathan Mayne (Supervisor)