The term ecocide refers to any extensive damage or destruction of the natural landscape and disruption or loss of ecosystem(s) of a given territory to such an extent that the survival of the inhabitants of that territory is endangered. Ecocide can be irreversible when an ecosystem suffers beyond self healing. It is generally associated with damage caused by a living agent whether directly or indirectly. An organism might inflict ecocide directly by killing enough species in an ecosystem to disrupt its structure and function. Ecocide can also result from pollution such as the introduction of high concentrations of pesticides which destroy the local flora extensively. A weaker definition of ecocide is that in which an organism destroys ecosystems other than its own. (e.g. cancer). For example, it could be said that during the Precambrian era, blue-green algae committed ecocide upon the prevailing reducing-chemistry-based ecology, by releasing oxygen into the environment. Organisms to which oxygen was a poison died off, while the algae and other organisms adapted and created a new oxidation-chemistry-based ecology.[citation needed]