What is the percentage of oxygen necessary for human life?

Earth's atmosphere must always contain 21% oxygen to maintain life.

Learn More:

• The Primitive Atmosphere by D Denner
• A Unique Blend by Dr. Danny R. Faulkner
• Worlds of Creation: Earth by Dr. Jason Lisle
• Oxygen Levels in the Early Earth's Atmosphere by Dr. Andrew A. Snelling
• Rapid Changes in Oxygen Isotope Content of Ice Cores by Dr. Larry Vardiman
• A World Without Oxygen?
• The Miracle of Air