Environmental pollution, in the classical concept, occurs when certain elements that cause harmful effects accumulate in quantities that nature cannot recycle. A contaminant is a substance that is found in a medium to which it does not belong or that does so at levels that can cause adverse effects. A species is in danger of extinction when its existence is globally compromised. Humans, in a short time, we have turned the Earth into a kind of supermarket where we are supplied with everything we need, including the spaces to build our towns, cities, mining camps, agricultural and livestock lands. We have wrested huge areas that recently belonged to the other species, without much regard to the damage we have caused them.