Life is an element that uniquely separates living and non living organisms and which entails the capacity to grow in a continuous process that culminates in eventual death. The Earth, among the none planets of the solar system, has proved successful in sustaining the life of both plants and animals. It has the appropriate environment that allows the survival and existence of every form of living. Therefore an astronaut who desires to find any evidence of living organisms that could exist in other planets needs to keep in mind the characteristics of living organisms as has been manifested on earth (Kotler& Armstrong, 1993).
Every form of living organism on earth that include plants, animals, fungi, bacteria having Carbon and based life have particular aspects in common. First, they possess complex genetical composition in the form of hereditary genes and cells. This where they are structured or organized into one or more cells which are the basic units of life. Second, have the ability to transform themselves into other forms through metabolism. This involves the transformation of energy by converting chemicals and energy into cellular components. These organisms are also able to decompose as well as maintain internal balance (homeostasis) and produce other forms associated with life (Kotler & Armstrong, 1993).
Another important characteristic is the capacity to maintain experience cell growth and maintain a balance of the cell fluids .This results in increase in size, of its parts and accumulated matter. This is achieved through respiration and excretion where wastes are disposed from the body. Of great significance also is the ability to respond to stimuli and sudden change in the environment. This happens through movement, chemical reactions through cell expansion. The living organisms are also able to reproduce through natural selection (Kotler& Armstrong, 1993). This is through either asexual reproduction or a sexual union between two parent organisms. The ability to adapt to the environment by change in response to the environment enhanced through evolution and the genetical structure of an organism as well as the metabolized substances and external factors present. The physical observation of the things found wil give evidence of their living nature.