When did the ozone layer become thick enough to provide an ...

[SO00]

When did the ozone layer become thick enough to provide an effective UV screen?
 
  What will be an ideal response?

Question 2

During the Soviet era, every Central Asian republic capital had a(n) ________.
 
  A) Orthodox Christian cathedral
  B) mosque converted to city hall
  C) opera and ballet theater
  D) statue of Lenin posing with a local legendary hero

[k2629]

Answer to Question 1

The O3 layer should have been absorbing most UV radiation by 2.3 Ga, as soon as O2 levels began to rise. An O2 level of 1 PAL is sufficient to create an efficient ozone screen.

Answer to Question 2

C

[SO00]

Excellent

[amit]

Great answer, keep it coming