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:
“He was discontented and wasted his life into the bargain; and yet he rated it as a gain in coming to America, that here you could get tea, and coffee, and meat every day. But the only true America is that country where you are at liberty to pursue such a mode of life as may enable you to do without these, and where the state does not endeavor to compel you to sustain slavery and war and other superfluous expenses which directly or indirectly result from the use of such things.”
—Henry David Thoreau (1817–1862)
“No country is so peaceful as the one that leads into death. Life arches above one’s head like a bridgespan, and below it flows the water, carries the boat, takes it further.”
—Alfred Döblin (1878–1957)
“I have almost forgot the taste of fears.
The time has been, my senses would have cooled
To hear a night-shriek, and my fell of hair
Would at a dismal treatise rouse and stir
As life were in’t. I have supped full with horrors;
Direness, familiar to my slaughterous thoughts,
Cannot once start me.”
—William Shakespeare (1564–1616)