The earliest human inhabitants of the earth were hunters and gatherers. Under favorable conditions they required at least 1.5 square kilometers to provide food for one person, and in harsher environments as much as 80 to 100 square kilometers. Population pressure eventually led humans to raise plants and animals.

With the introduction of agriculture, humans began to use energy to control the growth of plants and animals, to make more efficient use of the solar energy stored in plants by photosynthesis. However, for many thousands of years, the only energy used for this purpose was human energy. The energy drawn from the biosphere was limited to the dietary energy provided by plant food and meat, and to the use of wood and grasses as fuel for heating and cooking. Later, humans learned to use animal, water, and wind energy to obtain power for transport and for simple agricultural and industrial processes...