The role of Ozone in our Atmosphere
and Ozone Depletion

We learned earlier that the very early earth had little to no oxygen and that the first "living" things were probably Chemotrophic bacteria getting their energy to live from chemicals dissolved in the water. These organisms had to live at least a meter below the ocean's surface, so that the water could protect them from the harmful Ultra Violet energy from the Sun.
Later some of these organisms possed an adaptation that enabled them to use the energy of light to run processes in their bodies. These organisms were the beginning of Photosynthesizing organisms! They began to release molecular Oxygen (O2) into the atmosphere.

These organisms were better adapted for survival and reproduced more often than the others so they out competed the chemotrophs for space and resources in the first meter of the ocean.

Over time they became so numerous that their waste products (O2) began to build up in the atmosphere.
The build up of oxygen in the atmosphere allowed for the formation of the OZONE LAYER in the upper a part of the atmosphere called the Stratosphere. With the developement of the Ozone Layer, Organisms could live closer to the surface of the ocean and eventually on the land, because Ozone protects us from the harmful effects of Ultra Violet energy.

The development of the Ozone Layer works something like this:
Ozone is a form of oxygen with three oxygen atoms bonded together. It forms a protective shield in the Stratosphere about 12-20 Km up. Ozone absorbs harmful ultraviolet energy in the upper atmosphere, before it has a chance to make it to the surface. Here's how:
Ozone forms naturally when high energy ultraviolet energy strikes an "normal" oxygen (O2) molecule. The O2 molecule breaks apart leaving two free oxygen atoms (called free radicals).

The free oxygen atom combines with a "normal" O2 molecule to form Ozone (O3) notice that ozone has THREE oxygen atoms in it!!
Because of the shape of the ozone molecule it is able to absorb a lot of ultraviolet energy.

When U.V. energy strikes O3 the molecule absorbs it and begins to vibrate intensely converting the U.V. into HEAT! (Remember that heat is caused by motion of molecules?!!)

The vibration caused by the absorbtion of the U.V. energy causes ONE oxygen atom to break off the Ozone molecule leaving behind ONE atom of Oxygen and an O2 to start the process all over again!

The U.V. light is converted into heat and therefore is NOT U.V. anymore! The U.V. cannot make it to the surface to damage living things. This also causes the Stratosphere (the layer that has the ozone in it) to warm up a litle because the U.V. is converted to heat!

Ozone can be destroyed by Man Made Chemicals!
Chemicals called CloroFlouroCarbons (CFC's) destroy Ozone in the Stratosphere. CFC's were invented in the 1950's and were thought to be a wonder chemical.

They are non-toxic, evaporate quickly and are excellent for cleaning electronic parts.

They expand VERY rapidly when released so they make a GREAT propellant for spray cans. Since they are non-toxic they were used in everything from spray paint, to food service products, to under arm deodorants!!

They were used to expand foams like the kind that make seat cushions in cars and furniture to styrofoam.

Since they evaporate so rapidly they were used extensively as a refrigerant in air conditioners and refrigerators.

In 1978 it was realized that there might be a problem with these chemicals in the stratosphere. There is still a debate over the role of the CFC's in the depletion of the ozone layer.

Their use as propellants was phased out by 1980. In 1986 the Montreal Protocol called for the phase out of use as a refrigerant. The use of CFC's as a refrigerant was banned in most industrialized countries by the end of the 1990's. They are still in use in the electronics industry.
U.V. breaks a Chlorine atom (Cl) off of the CFC.

The Chlorine atom attaches to an ozone moleclue and breaks off a single atom of Oxygen.

The Chlorine+Oxygen combination then can combine with a free oxygen to make O2

That's the job the U.V. used to do!

If the Chlorine does it, then the U.V. passes right through to the surface! Oh Nooooo! :<

The Cl is then free to continue its dirty work!

There is no debate over the fact that the ozone layer IS getting thinner over the South Pole and shows signs of thinning over the North Pole.

A thinning of the Ozone Layer allows more of the harmful U.V. energy to reach the Earth's surface. U.V. energy causes the destruction of many molecules in living things. (not a good thing!) U.V. is VERY high energy radiation. The wavelength of Ultra Violet energy is close to the size of many molecules in living tissue.

When living tissue is struck by U.V. some of the molecules in a body are destroyed and can no longer function properly.

Damage from increased U.V. at the surface includes:
Increased skin cancer (especially malignant melanoma- a lethal form of skin cancer)
Destruction of DNA in phytoplankton (microscopic plant-like organisms) in the ocean. This is a LARGE problem because these organisms produce about 30% of the oxygen we breathe and are the base of the Marine Food Pyramid!

Increased cataracts (an eye disorder rendering the sufferer blind) in humans and herd animals grown for food.
Lowered crop yeilds due to damage to the plant. It should be obvious what problems this could cause! :<

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