Life (cf. biota) is a characteristic that distinguishes objects that have signaling and self-sustaining processes from those that do not, either because such functions have ceased (death), or else because they lack such functions and are classified as inanimate. Biology is the science concerned with the study of life.
Any contiguous living system is called an organism. Organisms undergo metabolism, maintain homeostasis, possess a capacity to grow, respond to stimuli, reproduce and, through natural selection, adapt to their environment in successive generations. More complex living organisms can communicate through various means. A diverse array of living organisms can be found in the biosphere of Earth, and the properties common to these organisms—plants, animals, fungi, protists, archaea, and bacteria—are a carbon- and water-based cellular form with complex organization and heritable genetic information.
Scientific evidence suggests that life began on Earth approximately 3.5 billion years ago. The mechanism by which life emerged is unknown and hypotheses are being formulated. Since then, life has evolved into a wide variety of forms, which biologists have classified into a hierarchy of taxa. Life can survive and thrive in a wide range of conditions. The meaning of life—its significance, origin, purpose, and ultimate fate—is a central concept and question in philosophy and religion. Both philosophy and religion have offered interpretations as to how life relates to existence and consciousness, and on related issues such as life stance, purpose, conception of a god or gods, a soul or an afterlife. Different cultures throughout history have had widely varying approaches to these issues.
Though the existence of life is only confirmed on Earth, many scientists believe extraterrestrial life is not only plausible, but probable. Other planets and moons in the Solar System have been examined for evidence of having once supported simple life, and projects such as SETI have attempted to detect transmissions from possible alien civilizations. According to the panspermia hypothesis, life on Earth may have originated from meteorites that spread organic molecules or simple life that first evolved elsewhere.
Other articles related to "life":
... The Russian orbital segment's life support systems are contained in the Service Module Zvezda ... The MLM Nauka laboratory has a complete set of life support systems ...
... of faith (i) faith in oneself, (ii) faith in the Master and (iii) faith in life ... Faith is so indispensable to life that unless it is present in some degree, life itself would be impossible ... It is because of faith that cooperative and social life becomes possible ...
... A biological half-life or elimination half-life is the time it takes for a substance (drug, radioactive nuclide, or other) to lose one-half of its pharmacologic, physiologic, or ... In a medical context, the half-life may also describe the time that it takes for the concentration in blood plasma of a substance to reach one-half of its steady-s ... For example, the biological half-life of water in a human being is about seven to 14 days, though this can be altered by his/her behavior ...
... Very little is known about Widukind's life ... There are no sources about Widukind's life or death after his baptism ... Abbey has been identified as a likely location where Widukind may have spent the rest of his life ...
... resources for organisms at any time throughout their life cycle ... between external and internal environments, however, is an abstraction parsing life and environment into units or facts that are inseparable in reality ... There is an interpenetration of cause and effect between the environment and life ...
Famous quotes containing the word life:
“Time, fall no more.
Let that be life time falls no more. The threat
Of time we in our own courage have forsworn.”
—Allen Tate (18991979)
“Quintilian [educational writer in Rome around A.D. 100] thought that the earliest years of the childs life were crucial. Education should start earlier than age seven, within the family. It should not be so hard as to give the child an aversion to learning. Rather, these early lessons would take the form of playthat embryonic notion of kindergarten.”
—C. John Sommerville (20th century)
“The secret of a long life is knowing when its time to go.”
—Michele Shocked (b. 1962)