Green plants developed until some emerged and grew along the beaches. Later, others invaded higher ground. Primitive animals developed in the seas and their descendants crept out to live on land. Green plants, in daytime, take in carbon dioxide and give off oxygen. At night the process is reversed.
Animals consume oxygen and exhale carbon dioxide.
As dead plants and animals decay, carbon dioxide is released into the air and nitrogen into the soil. However, because plants give off far more oxygen than they consume and take in far more carbon dioxide than they give off, the supply of oxygen in the air increased and that of carbon dioxide gradually dwindled. The dust, smoke, fumes and nuclear explosions produced by modern civilization threaten to disrupt that vital cycle of use and renewal. Argonne National Laboratory, Division of Educational Programs, Harold Myron, Ph.D., Division Director.