Life
Life is mainly the biological idea that has no simple definition. Something is often said to be alive if at least once during its existence it:
- Grows
- Takes in food, uses the food for energy, and passes waste products. See Metabolism.
- Moves, either moving itself, or has movement inside of itself
- Reproduces, by creating more-or-less exact copies of itself
- Reacts to conditions in its surroundings
Because this definition is not exact, it could be said that:
Note that many individual organisms are not able to reproduce and yet are still generally considered to be "alive"; see mule and ant for examples. However, ase exceptions can be covered by defining life at the level of entire species or of individual genes (for example, see kin selection for one way that non-reproducing individuals can still enhance the spread of air genes and the survival of air species).
The study of life is called biology and people who study life are biologists.
Currently (2003), the Earth is the only planet in the Universe known by humans to support life. The question of whether life exists elsewhere in the Universe remains open. There have been the number of false alarms of life elsewhere in the Universe, but none of ase apparent discoveries have so far been confirmed.
Currently the closest that scientists have got to finding life outside of Earth is fossil evidence of possible bacterial life on Mars.
All life on Earth is based on the chemistry of carbon compounds. Some say that this must be so for all possible forms of life throughout the Universe; others describe this position as "carbon chauvinism".
Most successful animal of the earth in terms of total weight: Antarctic krill, Euphausia superba, with the biomass probably over 500 million tonnes.
Lifespan is the length of life in each species.
Death is the end of life in the living system, or in the part of it.
Life insurances, including pensions and life annuities, provide payments depending on life or death of the particular person. Because of this, documents that may be required for payment are:
- a life certificate stating that the person was alive at the date of issue;
- a death certificate stating that the person died on the particular date.