Click on image for full size
What is Life?
What is life? If this strikes you as an odd question, consider it for a
moment. (It's almost as hard as describing the origin
of life). Of course we all have an intuitive sense of what life is, but
how would you actually define it? Given the incredible diversity of
living things, from the mold on your old tuna sandwich to monkeys in the
rainforest, how could one word encompass all that "life" represents?
Even biologists have a difficult time defining the very concept
they study. However, given our knowledge of the life forms present on
Earth, it is recognized that all living
things do share a set of characteristics in common:
1) Living things take in and use energy
2) Living things eliminate waste products
3) Living things grow and develop
4) Living things respond to their environment
5) Living things reproduce
6) Living things show variation based on heredity
7) Over time, living things evolve (change slowly) in response to their
Therefore, in order for something to be considered to be "alive" or to
"have life" as we know it, it must possess these characteristics.
Shop Windows to the Universe Science Store!
"Science, Evolution, and Creationism
", by the National Academies, provides fascinating background on these topics for all, and is particularly useful for the Earth and space science classroom. Check our other books
in our online store
You might also be interested in:
Jupiter's atmospheric environment is one of strong gravity, high pressure, strong winds, from 225 miles per hour to 1000 miles per hour, and cold temperatures of -270 degrees to +32 degrees (freezing temperature)....more
In July, 1996, it was announced that Dr. David McKay, along with a team of scientists at Johnson Space Center (a division of NASA), had discovered possible fossils of bacteria in an ancient rock from Mars....more
Saturn's atmospheric environment is one of strong gravity, high pressure, strong winds, from 225 miles per hour to 1000 miles per hour, and cold temperatures of -270 degrees to +80 degrees. With winds...more
Titan's atmosphere is a lot like the Earth's, except that it is very cold, from -330 degrees to -290 degrees! Like the Earth, there is a lot of Nitrogen and other complex molecules. There also may be an...more
Autotrophs are organisms that produce organic compounds from an inorganic source of carbon (carbon dioxide) given a source of energy. If the source of energy is the reactions of inorganic chemical compounds,...more
In the warm primordial ocean, aggregates of amino acids, proteins, and other hydrocarbons coalesced into a form called *coacervates*. Organic polymers such as amino acids will spontaneously form coacervates...more
Organisms that are able to make their own food (in the form of sugars) by using the energy of the Sun are called autotrophs, meaning "self-feeders". Photosynthesis is the name of the process through which...more