Earth’s early tectonic modes and implications for habitability - Peter A Cawood

Описание: Earth’s early tectonic modes and implications for habitability
Peter A Cawood
Monash University, Melbourne, Australia

Tectonic mode manifests how a planet’s interior is cooling, and it encompasses all the geological activities (e.g., magmatism, deformation, metamorphism, sedimentation) that characterize the planetary body. Tectonic processes exert first-order control on factors key to planetary habitability. For example, tectonic mode controls the long-term prevalence of surface oceans, the sustenance of physicochemical conditions (e.g., temperature) favourable for metabolic activity, fluxing of elements in and out of the planet’s interior and thereby, the availability of bio-essential nutrients (e.g., C, O, H, N, P, S). However, all tectonic modes do not regulate these processes efficiently. For example, stagnant-lid mode restricts heat and material exchange between a planet’s interior and surficial reservoirs compared to plate tectonics. Further, certain factors determining a planet’s tectonic mode – like internal heat budget, mechanical behaviour of rocks, and volatile content – can vary with time, leading to the prevalence of different tectonic modes during planetary evolution. Thus, a planet’s habitability is critically intertwined with its tectonic evolution.

Modern Earth is the only known planet with plate tectonics, felsic crust, and life. Plate tectonics has resulted in a Goldilocks environment for long-term habitability via chemical cycling across the Earth system, regulating temperature through the carbonate-silicate cycle, sustaining oceans at the surface, and developing bimodal hypsometry with emergent felsic crust releasing bio-essential minerals through weathering and erosion. This has resulted in diverse habitats facilitating life’s complex phylogenetic tree. However, life initiated on Earth in the Hadean or early Archean when non-plate-tectonic modes like the stagnant- or sluggish-lid modes are inferred to be prevalent. Our terrestrial planetary neighbours’ records suggest that such modes are unlikely to provide the environmental stability necessary to develop a long-term phylogenetic landscape. This talk focuses on the limited rock archive of the early Earth, along with knowledge of the other terrestrial planets, to discuss our planet’s early evolution.

Reference:
Cawood et al., 2022. Secular evolution of continents and the Earth system. Reviews of Geophysics, 60, e2022RG000789.