By using all green energies.
I would say photosynthetic bacteria are the most important, because if they disappeared most of the oxygen in the atmosphere wouldnt be here and complex life like humans wouldnt exist
A sudden change in the environment can cause something called Bottle-neck effect. Wherein it might affect the evolution of species in the area because it can reduce the size of the population at a rapid rate. This drop in population number can push be a 'bottle-neck' decrease of their size. In this case, certain alleles may be overrepresented among the survivors
