1.   Vegetation indirectly created the protective ozone shield by pumping oxygen into the atmosphere.

2.   If there were no ozone shield, plants and animals could not exist on land.

3.   Scientists hope to learn whether meteor storms degrade the ozone shield protecting life on earth from harmful ultraviolet radiation.

4.   This process of Antarctic dilution of the global ozone shield worsens the less severe depletion taking place throughout the world.