The ecological pressure for evolution came from the gradual depletion of the chemicals that were the source of energy, or if you will the food of the first life forms.
(The ecological pressure for evolution; came; from the gradual depletion of the chemicals) (the chemicals; were; the source of energy) (that; were the source of; energy)
The ecological pressure for evolution the chemicals that
came were were the source of
from the gradual depletion of the chemicals
the source of energy
energy