"And God said, Let there be a firmament in the midst of the waters, and let it divide the waters from the waters. And God made the firmament, and divided the waters which were under the firmament from the waters which were above the firmament: and it was so. And God called the firmament Heaven, And the evening and the morning were the second day." Genesis 1:6-8.
Our atmosphere components
The "Heaven" mentioned here as being created by God on the second day refers to our atmospheric heaven. It includes the air we breathe, and upon which life on earth depends. A 12-mile-thick layer wrapped around our planet, the atmosphere consists of about 78% nitrogen, 21% oxygen, and 1% argon, helium, carbon dioxide, and other gases. It also harbors a fair amount of water vapor and an unwarranted amount of pollution. As this mixture is inhaled into the lungs, about a fifth of the oxygen is retained while the rest is exhaled along with carbon dioxide and water vapor.
The human lung
The inside of the lung resembles a sponge. All of these tiny pockets (about 300 million) provide over seventy square yards of surface area for the exchange of gases in and out of the blood stream. An adult breathes about 16 times per minute, taking in about one pint of air per breath. This intake adds up to about 2,000 gallons of air per day. During normal breathing this air travels at about 50 miles per hour, but during a sneeze or cough it can reach speeds of 750 miles per hour. The maximum amount of air a person can inhale and exhale in one breath is called the vital capacity. A good vital capacity is related to a greater life expectancy. Several factors can affect a person's vital capacity: smoking, air pollution, posture, exercise, obesity, and shallow breathing.