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11.2: Characteristics and Origins of Life

Difficulty Level: Basic Created by: CK-12
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What is life?

How can you tell a blob of organic material from a living creature? What characteristics does something need to be considered alive? Does this photo resemble early Earth? Erupting geysers? Mats of bacteria? Maybe so! Of course, you have to ignore the trees in the distance.

The Origin Of Life

No one knows how or when life first began on the turbulent early Earth. There is little hard evidence from so long ago. Scientists think that it is extremely likely that life began and was wiped out. Possibly even more than once! If there was life, it would have been wiped out by the impact that created the moon.

This issue of what's living and what's not is important. It helps us to think about the origin of life. When does a blob of organic material become life? As you can see, we need to have a definition of life.

Characteristics of Life

To be considered alive, a molecule must:

  • be organic. The organic molecules needed are amino acids.
  • have a metabolism.
  • be capable of replication (be able to reproduce).

Amino acids are molecules of carbon, hydrogen, and oxygen. These molecules are called the building blocks of life because they create proteins. Proteins are complex organic molecules that make up cells. They are the most abundant class of biological molecules.

Learning About the Origin of Life

To look for information regarding the origin of life, scientists:

  • perform experiments to recreate the environmental conditions found at that time.
  • study the living creatures that make their homes in extreme environments. These environments are most like Earth’s early days.
  • seek traces of life left by ancient microorganisms, also called microbes (Figure below). These include microscopic features or chemistry left by life. It is very difficult to distinguish these from non-biological features.

Pictures of microbes

How can we tell where these microbes have been?



  • For something to be alive it must be organic, have a metabolism, and be capable of replication.
  • Amino acids create proteins. They are the building blocks of life.
  • To learn about the origins of life, scientists perform experiments. They study creatures that live in extreme environments. They look for traces of life that were left by ancient microbes.


  1. What are the characteristics of life?
  2. What are amino acids? Why are they important?
  3. What are proteins? If something doesn't have proteins can it be alive?
  4. How do scientists learn about the origins of life?

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    amino acid

    Organic molecules that are the building blocks of life.




    Essential organic material made of amino acids.

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    Difficulty Level:
    6 , 7
    Date Created:
    Jan 04, 2013
    Last Modified:
    Aug 29, 2016
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