Life is a characteristic that distinguishes physical entities that do have biological processes, such as signalling and self-sustaining processes, from those that do not, either because such functions have ceased, or because they never had such functions and are classified as inanimate. Various forms of life exist, such as plants, animals, fungi, protists, archaea, and bacteria. The criteria can at times be ambiguous and may or may not define viruses, viroids, or potential artificial life as “living”. Biology is the primary science concerned with the study of life, although many other sciences are involved. Some of the earliest theories of life were materialist, holding that all that exists is matter, and that life is merely a complex form or arrangement of matter. Empedocles argued that everything in the universe is made up of a combination of four eternal “elements” or “roots of all”: earth, water, air, and fire. All change is explained by the arrangement and rearrangement of these four elements. The various forms of life are caused by an appropriate mixture of elements. Death is the permanent termination of all vital functions or life processes in an organism or cell. EliteColumn brings you the 12 astonishing life quotes from several well-known personalities.