Couldn't find element LayerAd

Error finding content

What Is Life? - Windows to the Universe

Shop Windows to the Universe

Check out the fun Earth science related bumper stickers in our online store! Express yourself!
Short-eared owl
Click on image for full size
Corel Photography

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 environment.

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!

Traveling Nitrogen is a fun group game appropriate for the classroom. Players follow nitrogen atoms through living and nonliving parts of the nitrogen cycle. For grades 5-9.

Windows to the Universe Community



You might also be interested in:

Traveling Nitrogen Classroom Activity Kit

Check out our online store - minerals, fossils, books, activities, jewelry, and household items!...more

Can there be Life in the Environment of Jupiter?

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

The possible discovery of Life on Mars

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

The Environment of Saturn

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

The Environment of Titan, can there be Life?

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

Early Life

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

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part by the National Science Foundation and NASA, our Founding Partners (the American Geophysical Union and American Geosciences Institute) as well as through Institutional, Contributing, and Affiliate Partners, individual memberships and generous donors. Thank you for your support! NASA AGU AGI NSF