Natural Selection Image Map

Sulfur Travels By Land and Air

Certain types of bacteria perform photosynthesis using hydrogen sulfide (H2S) instead of water (H2O).  These bacteria most likely existed on earth before there was an abundance of atmospheric oxygen to use.  The early earth mainly consisted of volcanic lava, which contains large amounts of sulfur.  

Industrial waste is a major contributor to acid rain. Sulfur in the air can react to form a strong acid that comes back to earth when it rains.

Sulfur is exchanged locally and globally.  In the local exchange, sulfur is released from soil deposits by weathering and decomposition of organic and inorganic soil and rock deposits.  Sulfur exists in the air as hydrogen sulfide and sulfur dioxide.  Sulfur dioxide falls back to the earth in rain.  However, it becomes sulfuric acid (H2SO4) when it is combined with water.  This makes the rainwater acidic.  Most of the sulfur in air gets there by natural means.  However, the burning of fossil fuels and coal by humans adds a large amount of extra sulfur to the atmosphere.  What other cycle that we have already discussed contributes to acid rain?

Phosphorus Doesn’t Have Wings

Earlier we mentioned how glucose is used in the body to make energy in the Krebs Cycle.  The chemical form of energy produced in the Krebs Cycle is adenosine triphosphate (ATP).  This is an adenosine molecule with a chain of three phosphate (PO4) groups attached to it.  In addition to being contained in ATP, phosphate groups make up the backbone of DNA and RNA molecules.  In order to continually make ATP, DNA and RNA, the body needs a large supply of phosphate.  Phosphate is supplied to the body through the phosphorus cycle. 

If you examine a sample of atmosphere, you will not find any phosphorus.  All of the elements we have discussed so far can exist in the atmosphere as well as in soil and water.  Phosphorus does not have the ability to get into the atmosphere because it cannot escape as a gas.  If phosphorus ends up in an aquatic system such as a lake or an ocean, it has to stay there (it becomes immobilized).  

Most of the phosphorus present on earth is located in rocks.  The processes of weathering and erosion release phosphorus into the ecosystem.  Once phosphorus gets released into the ecosystem, it gets taken up by plants and eventually passed through the food chain.  Humans can disrupt the phosphorus cycle through the disposal of waste products and by using fertilizer.  Waste products end up in the sewage system where phosphorus becomes immobilized.  In fertilizer, phosphorus is stored in a compound called phosphate.  Phosphate reacts with other elements in the soil such as calcium, iron and aluminum and becomes immobilized.

You should have noticed that human actions in industry and agriculture have a major effect on the all of the cycles we have discussed.  Here is a summary of the major problems:

·   Possible global warming caused by the greenhouse effect of excess carbon dioxide

·   Acid rain is caused by nitrous oxide and sulfur dioxide

·   Immobilization of phosphorus makes it unavailable for cycling through plants and animals.

 

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