The Earth's core is divided into the liquid outer core (1,430 miles or 2,300 km radius) and the solid inner core (745 miles or 1,200 km radius).

The gaseous state occurs at a higher temperature range than the solid and liquid states of the same substance. In this state, molecules flow very freely around each other and will spread out as far as they're able. Gases maintain neither a constant volume nor a constant shape.

The heart is the organ that drives the circulatory system. In humans, it consists of four chambers with two that collect blood called atria and two that pump blood called ventricles. The heart's valves prevent blood pumped out of the ventricles from flowing back into the heart.

In the liquid state, molecules flow freely around each other and exist at a higher temperature range than the same substance in a solid state. Liquids maintain a constant volume but their shape depends upon the shape of their container.

The respiratory system manages respiration which is the process by which blood cells absorb oxygen and eliminate carbon dioxide.