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Earth is the only planet in the Universe from which life is known; the cradle and home of humanity, and of all known forms of life.


The word itself may refer to a living being or ongoing processes of which living things are a part of. It may also refer to the period during which something is functional (as between birth and death), the condition of an entity that has been born but yet has to die or that which makes a living thing alive.

The study of life is called biology, and people who study life are called biologists. A lifespan is the average length of life in a species. All known life on Earth is powered by solar energy. Without energy from the sun no life could exist. All life on Earth is based on the chemistry of carbon compounds, specifically involving long-chain molecules such as proteins and nucleic acid. With water, which is essential, the long molecules are wrapped inside membranes to form cells. This may or may not be true of all possible forms of life in the Universe: it is true of all life on Earth today.

Summary[change | change source]



At present, the Earth is the only planet we have detailed information about. The question of whether life exists elsewhere in the Universe is open. There have been a number of claims of life elsewhere in the Universe. None of these have been confirmed so far. The best evidence of life outside of Earth is are nucleic acids that have been found in certain types of meteorites[3].

Definitions of life[change | change source]

One explanation of life is called the cell theory. The cell theory has three basic points: all living things are made up of cells. The cell is the smallest living thing that can do all the things needed for life. All cells must come from pre-existing cells.

Something is often said to be alive if it:


  • Mules cannot reproduce, and neither can worker ants.
  • Viruses and spores are not actively alive (metabolising) until the conditions are right.



A modern approach[change | change source]

A modern definition was given by Humberto Maturana and Francisco Varela in 1980,[4] to which they gave the name autopoiesis:

  1. The production of their own components
  2. The correct assembly of these components
  3. Continuous repair and maintenance of their own existence.

Roth commented that "In short, organisms are self-reproducing and self-maintaining, or 'autopoietic', systems".[5] This approach makes use of molecular biology ideas and systems science ideas.

Gallery of images of life[change | change source]

Related pages[change | change source]

References[change | change source]

  3. Zita Martins; Oliver Botta, Marilyn L. Fogel, Mark A. Sephton, Daniel P. Glavin, Jonathan S. Watson, Jason P. Dworkin, Alan W. Schwartz, Pascale Ehrenfreund (2008). "Extraterrestrial nucleobases in the Murchison meteorite". Earth and Planetary Science Letters 270: 130-136. Retrieved 2015-03-10. 