The first signs of life appeared in the ocean 3.5 billion years ago, and over the years those early single-celled organisms evolved into the diverse life we see today, on land as well as in the sea. Most of the major branches of the Tree of Life (diagrams showing evolution and relationships between species) are located in the ocean.

 All living things need water to survive. Water helps transport oxygen, minerals, nutrients, and waste products to and from cells. The digestive system needs water to function properly, and water lubricates the mucous membranes in the respiratory and digestive tracts. Water serves as a medium for metabolic functions and other chemical reactions that generate energy in the body. Water regulates body temperature (by perspiration and respiration) and acts as a cushion between the spinal cord and brain and between joints in the skeletal system.

 In some organisms, up to 90% of body weight is water. Up to 60% of the adult body is water, of which the brain and heart are 73% water, the lungs are about 83% water, the skin is 64% water, the muscles and kidneys are 79%, and even the bones contain water: 31%.

 Humans must consume a certain amount of water every day to survive. It depends on age, gender, and where you live, but in general, adult men need about 3 liters per day and adult women need about 2.2 liters per day. This amount of water is obtained not only through direct drinking but also from the food we eat.