Thermal adaptation evolution and dispersal of the terrestrial biosphere regulates Earth’s long-term climate

Sustained habitable conditions and the evolution of complex life on Earth depend on efficient climate regulation mechanisms that keep carbon fluxes between geologic reservoirs and the atmosphere-ocean system in balance. The terrestrial biosphere plays an important role in regulating the long-term climate by controlling burial rates of photosynthetically fixed CO₂ as well as by mediating CO₂ consumption through silicate mineral weathering during plant nutrient acquisition. These long-term carbon sinks balance out carbon inputs to the atmosphere-ocean system by processes including volcanism or the oxidative weathering of buried organic carbon. Current biogeochemical models of the Phanerozoic Earth neglect that the strength of the impact of the terrestrial biosphere on global carbon fluxes is subject to evolutionary dynamics and that it depends on how well the biosphere is adapted to prevailing environmental conditions [1]. Here, we develop a theoretical model to reconstruct global organic and inorganic carbon fluxes over the last 390 Myrs. The model includes eco-evolutionary processes underlying the thermal adaptation, such as the dispersal of terrestrial biomes in response to climatic changes and the in situ adaptive evolution towards the local environment. We show that the speed of evolutionary adaptation of the terrestrial biosphere to climatic shifts strongly affects the long-term atmosphere-ocean carbon mass balance. When considering a slow rate of thermal adaptation of the biosphere, resulting in reduced organic carbon burial and silicate weathering rates following temperature shifts, a closer balance of reconstructed Phanerozoic carbon inputs and outputs to and from the atmosphere-ocean system is obtained. Such a balance is a prerequisite to maintain habitable conditions on Earth’s surface on a multi-million-year timescale. We argue that the climate evolution of the Phanerozoic Earth is strongly defined by biological and evolutionary processes. Understanding these biological dynamics and how they shape the interactions between Earth’s biosphere, geosphere and the climate system may help to understand large shifts in Phanerozoic temperatures and the development of the atmospheric composition of the planet.

[1] Mills, B.J. et al. Modelling the long-term carbon cycle, atmospheric CO2, and Earth surface temperature from the late Neoproterozoic to present day. Gondwana Research 67, 172-186. DOI: 10.1016/j.gr.2018.12.001