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.
Read more about Life: Definitions, Origin, Conditions, Form and Function, Classification, Extraterrestrial Life, Death, Artificial Life
Other articles related to "life":
... Very little is known about Widukind's life ... There are no sources about Widukind's life or death after his baptism ... where Widukind may have spent the rest of his life ...
... 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-state value (the "plasma half-life") ... 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 ...
... 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 ...
... resources for organisms at any time throughout their life cycle ... The distinction 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 ...
... (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 ...
Famous quotes containing the word life:
“But the divinest poem, or the life of a great man, is the severest satire.... The greater the genius, the keener the edge of the satire.”
—Henry David Thoreau (1817–1862)
“Personal change, growth, development, identity formation—these tasks that once were thought to belong to childhood and adolescence alone now are recognized as part of adult life as well. Gone is the belief that adulthood is, or ought to be, a time of internal peace and comfort, that growing pains belong only to the young; gone the belief that these are marker events—a job, a mate, a child—through which we will pass into a life of relative ease.”
—Lillian Breslow Rubin (20th century)
“The East is the hearthside of America. Like any home, therefore, it has the defects of its virtues. Because it is a long-lived-in house, it bursts its seams, is inconvenient, needs constant refurbishing. And some of the family resources have been spent. To attain the privacy that grown-up people find so desirable, Easterners live a harder life than people elsewhere. Today it is we and not the frontiersman who must be rugged to survive.”
—Phyllis McGinley (1905–1978)