How are the earth’s principal biological systems being depleted?

The earth has four principal biological systems. Namely the fisheries, forests, grasslands, and croplands. These four systems not only are the basic systems needed for livelihood but are also the root sources of raw materials for most of our needs. In short they for the main structure of the World Economy. But today, with the growing demands in things like protein, the demand for fish is constantly increasing. To fulfill this demand, the fish stock is being exhausted. In addition to supplying our food, these four systems provide virtually all the raw materials for industry except minerals and petroleum-derived synthetics. In large areas of the world, human claims on these systems are reaching an unsustainable level, a point where their productivity is being impaired. When this happens, fisheries collapse, forests disappear, grasslands are converted into barren wastelands, and croplands deteriorate. In a protein-conscious and protein-hungry world, over-fishing is common every day. In poor countries, local forests are being decimated in order to procure firewood for cooking. In some places, firewood has become so expensive that “what goes under the pot now costs more than what goes inside it