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:
“What if there are not only two nostrils, two eyes, two lobes, and so forth, but two psyches as well, and they are separately equipped? They go through life like Siamese twins inside one person.... They can be just a little different, like identical twins, or they can be vastly different, like good and evil.”
—Norman Mailer (b. 1923)
“You’ll have to learn that public life takes a lot of sweat; but it doesn’t need to worry you. You won’t always be right, but you mustn’t suffer from being wrong. That’s what kills people like us.”
—Franklin D. Roosevelt (1882–1945)
“The symbol of perpetual youth, the grass-blade, like a long green ribbon, streams from the sod into the summer, checked indeed by the frost, but anon pushing on again, lifting its spear of last year’s hay with the fresh life below. It grows as steadily as the rill oozes out of the ground.... So our human life but dies down to its root, and still puts forth its green blade to eternity.”
—Henry David Thoreau (1817–1862)