Life

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

Famous quotes containing the word life:

    The man Shelley, in very truth, is not entirely sane, and Shelley’s poetry is not entirely sane either. The Shelley of actual life is a vision of beauty and radiance, indeed, but availing nothing, effecting nothing. And in poetry, no less than in life, he is “a beautiful and ineffectual angel, beating in the void his luminous wings in vain.”
    Matthew Arnold (1822–1888)

    All mothers need instruction, nurturing, and an understanding mentor after the birth of a baby, but in this age of fast foods, fast tracks, and fast lanes, it doesn’t always happen. While we live in a society that provides recognition for just about every life event—from baptisms to bar mitzvahs, from wedding vows to funeral rites—the entry into parenting seems to be a solo flight, with nothing and no one to mark formally the new mom’s entry into motherhood.
    Sally Placksin (20th century)

    They who are continually shocked by slavery have some right to be shocked by the violent death of the slaveholder, but no others. Such will be more shocked by his life than by his death.
    Henry David Thoreau (1817–1862)