Oxygen - BioInteractive
Oxygen, is a lung friendly chemical element discovered by three researchers, working independently in the 1770's in England, Sweden, and France. Abundant in the earth's atmosphere for 2.3-2.4 billion years, air is typically 21% oxygen, required by humans for proper cell metabolism. Scientists contend that during a period of geologic history oxygen constituted 35% of the earth's atmosphere. Such a high concentration of oxygen was too high to sustain life on earth as we know it. 21% is optimal for sustaining life on our planet.