Avoid? Am I kidding myself? Oxygen means so much to us. Yet in the larger context of biosphere, it not only is harmful, but is rather toxic to many bacteria — the dominant life form on Earth. To survive, life must avoid any toxic substance.

The earliest bacteria lived deep in the ocean floor. The Earth was free from oxygen molecules back then. Atmosphere was a mixture of nitrogen and carbon dioxide. It was all peaceful some three billion years ago. Then some adventurous bacteria invented a machinery to harness sunlight for making stored energy. We know the process by the name of…