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
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... 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 ...
... 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 ... of faith that cooperative and social life becomes possible ...
... and contains resources for organisms at any time throughout their life cycle ... however, is an abstraction parsing life and environment into units or facts that are inseparable in reality ...
Famous quotes containing the word life:
“His life itself passes deeper in nature than the studies of the naturalist penetrate; himself a subject for the naturalist. The latter raises the moss and bark gently with his knife in search of insects; the former lays open logs to their core with his axe, and moss and bark fly far and wide. He gets his living by barking trees. Such a man has some right to fish, and I love to see nature carried out in him.”
—Henry David Thoreau (1817–1862)
“Among the earliest institutions to be invented, if I read the stars right, is a Protestant monastery, a place of elegant seclusion where melancholy gentlemen and ladies may go to spend the advanced session of life in drinking milk, walking the woods & reading the Bible and the poets.”
—Ralph Waldo Emerson (1803–1882)
“If it is asserted that civilization is a real advance in the condition of man,—and I think that it is, though only the wise improve their advantages,—it must be shown that it has produced better dwellings without making them more costly; and the cost of a thing is the amount of what I will call life which is required to be exchanged for it, immediately or in the long run.”
—Henry David Thoreau (1817–1862)