When the environment is full of abundance. There was no pollution and weather have left to eat the remaining resources are used because in the past there was little population and continuous valuable resources.
When the environment is filled with an abundance of air pollution and resource surplus. For in the days before the less populated and valuable resource.
In the past, the environment will be filled with plenty, the air is good, no pollution, and a remaining amount to eat the waste. In the past, and has a population of a few resource use value.