  Life on Earth has experienced numerous upheavals over its approximately 4
billion year history. In previous work we have discussed how interruptions to
stability lead, on average, to increases in habitability over time, a tendency
we called Entropic Gaia. Here we continue this exploration, working with the
Tangled Nature Model of co-evolution, to understand how the evolutionary
history of life is shaped by periods of acute environmental stress. We find
that while these periods of stress pose a risk of complete extinction, they
also create opportunities for evolutionary exploration which would otherwise be
impossible, leading to more populous and stable states among the survivors than
in alternative histories without a stress period. We also study how the
duration, repetition and number of refugia into which life escapes during the
perturbation affects the final outcome. The model results are discussed in
relation to both Earth history and the search for alien life.
