Which is not true about the ozone layer?

Question

It shields Earth from most ultraviolet radiation

its thickness has remained constant overtime

its made of o3

CFC molecules can destroy ozone molecules

it s predicted that a reduction of this layer can increase human skin cancer.

Answer 1

They're all true apart from the second statement - "its thickness has remained constant overtime".

There are seasonal and geographical changes which affect the thickness of the ozone layer.  Typically the layer thickens as you move towards the polar regions and is reaches a peak thickness in spring; the main reasons for this variation is solar variation and atmospheric circulation.

Something known as Free Radical Catalysts can destroy ozone and this was happening until fairly recently, largley through the use of chloroflourocarbons (CFC's).  This led to a depletion in ozone levels.  New laws and regulations have been introduced banning CFC's and the 'hole' in the ozone layer that was causing much concern 10 - 20 years ago is now much reduced.