The structure of the earth is divided into four major components: the crust, the mantle, the outer core, and the inner core. 

 vitamin D to absorb calcium and promote bone growth. 

Pathology is the study of the causes and effects of disease or injury. 

Biogenesis is the production of new living organisms.

The air in Earth's atmosphere is made up of approximately 78 percent nitrogen and 21 percent oxygen.

Air also has small amounts of lots of other gases, too, such as carbon dioxide, neon, and hydrogen.