Life 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 at least 3.5 billion years ago. The earliest evidences for life on Earth are graphite found to be biogenic in 3.7 billion-year-old metasedimentary rocks discovered in Western Greenland and microbial mat fossils found in 3.48 billion-year-old sandstone discovered in Western Australia. The mechanism by which life emerged on Earth is unknown, although many hypotheses have been 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.
Though the existence of life is confirmed only on the planet Earth, many scientists think that extraterrestrial life is not only plausible, but probable or even inevitable. 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 radio transmissions from possible alien civilizations. According to the panspermia hypothesis, microscopic life exists throughout the Universe, and is distributed by meteoroids, asteroids and planetoids.
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.
Reflections on Life:
The above excerpt from the Wikipedia article begins with a biological discussion of life and ends by asking the philosophical and religious questions about the meaning of life. Some scientists in the tradition of “reductive scientism” believe that “science alone” can and should answer to question about “the meaning of life,” even if its answer must be that there is no answer, or that the question itself is not meaningful, or that it is simply to survive and pass on one’s genes to the next generation. Likewise, the question as to whether organic life, and especially complex, adaptive and emergent forms of conscious, intelligent and creative life have a transcendent value and purpose can be variously discussed under the rubrics of science, philosophy and religion. When it comes to discussing the fundamental questions of life, there is not doubt that worldview assumptions, beliefs, values and commitments come into play.