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":
... contains resources for organisms at any time throughout their life cycle ... environments, however, is an abstraction parsing life and environment into units or facts that are inseparable in reality ... interpenetration of cause and effect between the environment and life ...
... (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 ... because of faith that cooperative and social life becomes possible ...
... Very little is known about Widukind's life ... There are no sources about Widukind's life or death after his baptism ... has been identified as a likely location where Widukind may have spent the rest of his 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 ...
... 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 ... 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-state ... 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 ...
Famous quotes containing the word life:
“If a walker is indeed an individualist there is nowhere he cant go at dawn and not many places he cant go at noon. But just as it demeans life to live alongside a great river you can no longer swim in or drink from, to be crowded into safer areas and hours takes much of the gloss off walkingone sport you shouldnt have to reserve a time and a court for.”
—Edward Hoagland (b. 1932)
“All my life I believed I knew something. But then one strange day came when I realized that I knew nothing, yes, I knew nothing. And so words became void of meaning ... I have arrived too late at ultimate uncertainty.”
—Ezra Pound (18851972)
“Ma, sooner or later there comes a point in a mans life when hes gotta face some facts. And one fact Ive got to face is whatever it is women like, I aint got it.”
—Paddy Chayefsky (19231981)