27 Sep 2023
 | 27 Sep 2023
Status: this preprint is currently under review for the journal ESD.

Gaia: Complex systems prediction for time to adapt to climate shocks

Allen G. Hunt, Muhammad Sahimi, Boris Faybishenko, Markus Egli, Zbigniew J. Kabala, Behzad Ghanbarian, and Fang Yu

Abstract. Earth’s climate has undergone significant fluctuations in the geologic past. We focus on the glacial episodes that followed the major waves of invasion of land plants. Twice in Earth’s history the impacts of land plant innovations on the atmosphere through increased CO2 drawdown have precipitated sufficient cooling to produce ice ages. Each time, however, adaptation of soil ecosystems eventually helped re-establish apparent steady-state conditions, i.e., new equilibrium temperature and atmospheric CO2 content, ending each of the glacial episodes. In each case, the time interval between the initial innovation and the emergence from the glacial episode was approximately 60 Myr. The consistency of the time scale of the response invites an explanation in terms of a universal rate of dispersal of genetic information that encapsulates the biogeochemical cycle of cellulose production and decay. In this paper, we postulate that the long time for adaptation is a consequence of the time required for the spread of an entire clade though the soil to continental scale. Although 60 Myr appears to be a long time, it is very short compared to the time required for diffusion to transport even molecules like HCO3 or sugar through the soil over a continental distance of 5,000 km, which is between 1014 and 1016 years for solutes with such soil diffusion constants in the range 10−11 m2 s−1. Horizontal solute transport through heterogeneous media by advection might be considered as a dispersal mechanism, but is also known to require enormous time scales (ca. 150 Myr for 500 m). We also seek a relevant mechanism in the known scaling of plant and fungal growth rates as a function of time, which can facilitate as well the movement of bacteria, and predicted these rates theoretically on the basis of the universal optimal 2D paths tortuosity from percolation. Comparison with actual data pairs (7,000) for plant and fungal growth rates were used to verify these predictions over 13 orders of magnitude of time, from about one minute to 100 kyr; extrapolation over less than three additional orders of time yields a continental-scale transport time of 80 Myr. We now interpret this prediction in terms of Margulis’ understanding of emergent behavior of coupled (soil and plant) ecosystems responding to climate shocks induced by plant innovations.

Allen G. Hunt et al.

Status: open (until 21 Dec 2023)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on esd-2023-21', Stefano Manzoni, 02 Oct 2023 reply
    • CC1: 'Reply on RC1', Allen G. Hunt, 08 Oct 2023 reply

Allen G. Hunt et al.

Data sets

Biological and physical transport processes: Gaia A. G. Hunt, M. Sahimi, B. Faybishenko, M. Egli, Z. J. Kabala, B. Ghanbarian, and F. Yu

Allen G. Hunt et al.


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Short summary
Relative stability of Earth’s climate system is considered an emergent property of coupled ecosystems. We apply a spatio-temporal scaling relation for root growth to couple bacterial/fungal/vegetational response to climate crises triggered by land plant invasion and predict an absolute time scale to reach homeostasis. The predicted time is 33 % larger than required for the biosphere to emerge from associated Paleozoic ice ages. We propose a basis for understanding the biosphere and critical zone.