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The Origin of Life (The Atmosphere of Early Earth (Modeling Conditions on…

- - - - "On ancient Earth, nitrogen, water vapor, carbon dioxide, and methane were probably the most abundant gases in the atmosphere."
        
        Today the major gases in the atmosphere are nitrogen and oxygen.
  - - - There was no oxygen and organisms like you could not breathe.
        
        No one knows what the first forms of life were but scientists think that the first living forms did not need any oxygen.
        
        They were probably unicellular organisms.
        
        They probably lived in the oceans.
        
        The first organisms probably looked like the archaea that live today in harsh environments like in polar ice caps, hot springs, and the mud of ocean bottoms.
  - - - Although Redi and Pasteur showed that living things do not spontaneously arise from nonliving things on today's Earth, scientists do believe that the first life forms probably did arise from nonliving materials.
    - - Both of them designed an experiment in which they recreated the conditions of early Earth in their laboratory.
        
        They placed water to demonstrate the ocean and a mixture of the gases that they thought to compose Earth's early atmosphere into a flask.
        
        They were careful and tried to keep unicellular organisms and oxygen out of there mixture.
        
        They then sent an electric current through the mixture to simulate lightning.
        
        In about a week the mixture had become darker.
        
        In the darkened mixture Stanley Miller and Harold Urey found these small chemical units that if joined together could form proteins. This was one of the building blocks of life.
- - - - A fossil is the remains of an ancient organism that has been preserved in a rock or a other substance.
        
        Scientists have discovered fossils that look like archaea-like organisms.
        
        The ancient fossils that were discovered are dated to be up to 3.4 billion and 3.5 billion years old.
        
        These fossils give evidence that these cells could have existed back then.
    - - They were probably heterotrophs and they used the chemicals in their surroundings for energy.
        
        As cells grew and reproduced there numbers rised.
        
        The amount of chemicals that were available decreased.
    - - The autotrophs from the past had an important effect on today's atmosphere.
        
        When they made there own, they produced oxygen as a waste product.
        
        As the autotrophs did very well, oxygen grouped together on the Earth's atmosphere.
        
        The amount of oxygen increased to the amount current level that there is today over hundreds of millions of years.
    - - A lot of scientists continue to explore the questions about how and where life first arose on Earth today.
        
        Laboratory experiments like the ones that Stanley Miller and Harold Urey did can never prove how life first appeared on Earth.
        
        Those experiments can only hypotheses about life forms that might have arisen.
        
        No one knows how life first appeared on Earth.
        
        Scientists will continue to ask questions, test their models, and look for experimental fossil evidence about the origin of life on Earth.