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

A proposal, called “Gaia”, that life regulates Earth’s climate to its advantage, is partially supported by Earth’s climate history, wherein temperature fluctuations over the past ca. half billion years have mostly been small enough to protect life from extremes of climatic fluctuations, while global temperatures overall cooled during the 3.8 Ga when life was present, in spite of increased solar irradiance. Kirchner states that the simultaneous existence of bi-directional and uni-directional responses is inconsistent with the understanding of the effects of a single organism. Further, the counterargument that plant life creates climate crises endangering life’s survival has been advanced. These two objections require a more nuanced understanding of the biosphere as interacting, nested, ecosystems. It has also been asserted that chemical weathering provides negative feedback to climate fluctuations due to its strong temperature dependence, making it a global thermostat. However, this suggestion is based on the failure to recognize that chemical weathering rates in situ, unlike the lab, are limited by water fluxes. Since warmer temperatures need not support increased precipitation, particularly at times corresponding to the assembly of supercontinents, weathering is unsuited as a thermostat. Here, we present quantitative predictions of the time required, 80 Ma, for a synergistic system of plants/bacteria/fungi to reach continental size. Although the prediction was originally applied to the wrong biosphere adaptation, we now show that 80 Ma exceeds by only 33% the time required (60 Ma) for Earth to return to homeostasis after biological innovations of land plants ultimately plunged Earth into Paleozoic ice ages. This alternate understanding provides a rationale to examine further the potential for soil ecosystem adaptation to deliver the homeostatic response implied in the Gaia “hypothesis.”