  The Gaia hypothesis postulates that life regulates its environment to be
favorable for its own survival. Most planets experience numerous perturbations
throughout their lifetimes such as asteroid impacts, volcanism, and the
evolution of their host star's luminosity. For the Gaia hypothesis to be
viable, life must be able to keep the conditions of its host planet habitable,
even in the face of these challenges. ExoGaia, a model created to investigate
the Gaia hypothesis, has been previously used to demonstrate that a randomly
mutating biosphere is in some cases capable of maintaining planetary
habitability. However, those model scenarios assumed that all non-biological
planetary parameters were static, neglecting the inevitable perturbations that
real planets would experience. To see how life responds to climate
perturbations to its host planet, we created three climate perturbations in
ExoGaia: one rapid cooling of a planet and two heating events, one rapid and
one gradual. The planets on which Gaian feedbacks emerge without climate
perturbations are the same planets on which life is most likely to survive each
of our perturbation scenarios. Biospheres experiencing gradual changes to the
environment are able to survive changes of larger magnitude than those
experiencing rapid perturbations, and the magnitude of change matters more than
the sign. These findings suggest that if the Gaia hypothesis is correct, then
typical perturbations that a planet would experience may be unlikely to disrupt
Gaian systems.
