2.5 million years ago the first genus Homo evolves.
Photosynthesis is crucial for life on this planet, if photosynthesis did not happen the glucose on this planet would be used up quickly ,leaving no energy in a usable form; therefore ending life on this planet.
The Major function of the respiratory system is to exchange oxygen and carbon dioxide. Inhaled oxygen enters the lungs and reaches the alveoli, the layers of the cells lining the alveoli and the surrounding capillaries are each only one cell thick and are in very close contact with each other, the barrier between air and blood averages about 1 micron in thickness. Oxygen diffuses quickly through the air-blood barrier into the blood in the capillaries. Similarly, carbon dioxide passes from the blood into the alveoli and is then exhaled.
