The rest forms the higher energy environment relative to which Life creates its energy differential. By allowing relatively small amounts of input energy to flow through the system at strategic points, the organic system moves a greater amount of mass into the more complex higher order lifeforms - which have a lower energy density. Most plants are relatively short lived and their accumulated biomass dropped out of the organic system fairly quickly before the advent of animals. By consuming plants and transforming their biomass into ever more complex structures, animals further concentrate the elemental mass drawn into the organic system by the plants. Once elemental mass has been drawn into the organic system, the complex recursive structure of the ecosystem keeps it in the system by recycling it through carnivores, scavengers, various agents of decay - and if all else fails, once again the plants.
Life works on many levels in response to entropy.
In a world powered by the latent energy of combustible hydrocarbons, it's hard to conceive of organic materials like gasoline or naphtha as having a low energy density. In addition, most organic materials created by Life are relatively stable and represent substantially lower energy densities than their previous unbound forms. The stronger the bond, the greater the number of shared electrons, the more complete the outer shells of all participating molecules, and the more stable the resulting assembly. Collections of bound molecules assemble into cells, which by means of bonding and other chemical interactions, further lower the energy density of the component molecules. Cells are then grouped into ever larger organic structures - commonly referred to as organisms.