Life
Evidence suggest that life on Earth has existed for about 3.7 billion years. All known life forms share fundamental molecular mechanisms, and based on these observations, theories on the origin of life attempt to find a mechanism explaining the formation of a primordial single cell organism from which all life originates. There are many different hypotheses regarding the path that might have been taken from simple organic molecules via pre-cellular life to protocells and metabolism.
Although there is no universal agreement on the definition of life, scientists generally accept that the biological manifestation of life is characterized by organization, metabolism, growth, adaptation, response to stimuli and reproduction. Life may also be said to be simply the characteristic state of organisms. In biology, the science of living organisms, "life" is the condition which distinguishes active organisms from inorganic matter, including the capacity for growth, functional activity and the continual change preceding death.
A diverse array of living organisms (life forms) can be found in the biosphere on Earth, and 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. Living 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.
Read more about this topic: Natural Environment
Famous quotes containing the word life:
“My advice to people today is as follows: If you take the game of life seriously, if you take your nervous system seriously, if you take your sense organs seriously, if you take the energy process seriously, you must turn on, tune in, and drop out.”
—Timothy Leary (b. 1920)
“Conventional wisdom notwithstanding, there is no reason either in football or in poetry why the two should not meet in a man’s life if he has the weight and cares about the words.”
—Archibald MacLeish (1892–1982)
“It might be seen by what tenure men held the earth. The smallest stream is mediterranean sea, a smaller ocean creek within the land, where men may steer by their farm bounds and cottage lights. For my own part, but for the geographers, I should hardly have known how large a portion of our globe is water, my life has chiefly passed within so deep a cove. Yet I have sometimes ventured as far as to the mouth of my Snug Harbor.”
—Henry David Thoreau (1817–1862)