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).

Approximately every 28 days during female ovulation an egg (ovum) is released from one of the ovaries and travels through the oviduct (fallopian tube) and into the uterus. At the same time, the endometrial lining of the uterus becomes prepared for implantation.

Found in both animal sources (meat, fish, eggs, cheese) and vegetables (beans, nuts, some grains), proteins are important for the body's maintenance, growth, and repair.

Tough fibrous cords of connective tissue called tendons connect muscles to the skeleton while another type of connective tissue called ligaments connect bones to other bones at joints (elbow, knee, fingers, spinal column).

The water (hydrologic) cycle describes the movement of water from Earth through the atmosphere and back to Earth. The cycle starts when water evaporates into a gas from bodies of water like rivers, lakes and oceans or transpirates from the leaves of plants.