MadSci Network: Evolution

Re: The origins of simple orgasnisms

Area: Evolution
Posted By: Chris Yost, Grad student Microbiology
Date: Wed Apr 10 16:32:16 1996


You are correct about the belief that pre-biotic earth had high volcanic activity and electrical storms. The other important factor that needs to be included before we can predict how organic compounds were formed is the chemical environment on pre-biotic earth. The main chemical compounds believed to be present were methane, carbon monoxide, ammonia, hydrogen (all gaseous), and water. The formation of some of these inorganic compounds could be attributed to the volcanic activity.

The basic theory is that organic compounds were formed by chemical reactions between the inorganic compounds listed above. This theory was first tested by Miller and Urey in 1953. These researchers simulated pre-biotic earth in a lab environment. In a closed system they added gaseous methane, ammonia, hydrogen, and water vapor. They subjected this system to electrical discharges. A cooling condenser was attached to the system which would cool the water vapor to liquid. This liquid would contain any soluble compounds formed during the experiment. When the liquid was collected and analyzed the researchers found a variety of organic compounds, including some amino acids. Ok, assuming this happened on earth, monomeric organic compounds could have accumulated. What is the next step to life?

The monomeric molecules needed to polymerize into more complex molecules. A polymerization reaction can be a dehydration reaction where two monomers bond together by releasing a water molecule. A substratum would be necessary for the monomers to concentrate together in order to polymerize. In the laboratory, researchers have demonstrated polymerization by dripping a dilute concentration of monomers onto hot sand or clay (simulating hot volcanic rock). Perhaps dilute monomers were splashed onto hot lava by waves or rain. Then these polymers were washed back into the ocean. It is possible that these polymers formed aggregates. Researchers have termed these aggregates protobionts. Protobionts show some properties of life. They can contain permeable protein membranes and therefore have a chemical environment different from the surrounding environment. The big step towards formation of life would have been macromolecules that could self-replicate. It is believed that RNA was one of the first molecules capable of self-replication. There is still many gaps in our knowledge of how simple organic monomers could form polymers capable of creating life. It is a very fascinating area of research.

I have listed some references which may be relevant. I hope they will stimulate a whole new series of questions for you.

Emsley, J. 1994. Babies born to artificial cells. New Scientist (April 9).

Orgel, L. E. 1994. The origin of life on earth. Scientific American (October)

Rebek, J. 1994. Synthetic self-replicating molecules. Scientific American (July)

Chris Yost

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