Conditions for Life: Energy One property of life that everybody agrees on is that living systems are energy transformers. Life requires energy. It transforms different sources of energy (radiation, photochemical products, minerals, reduced gases) to useful cellular energy systems (electrochemical gradients, ATP or reducing power). Although we believed for many years that life on Earth was dependent on solar energy, the discovery of chemolithotrophic organisms that get energy only from minerals or reduced gases (in the absence of light) has produced a real revolution in biology. This has expanded enormously the possibilities of finding life in the universe and has lead scientists to consider alternative scenarios for the origin and early evolution of life on Earth.