About 540 million years ago, a sudden increase in biological ...

[aabwk4]

About 540 million years ago, a sudden increase in biological complexity occurred, known as the _______________.
 
  Fill in the blank(s) with correct word

Question 2

As Earth evolved with life, an oxygen abundance of only 0.1 percent would have created a(n) _______________, protecting organisms from the Sun's ultraviolet radiation.
 
  Fill in the blank(s) with correct word

[Mollythedog]

Answer to Question 1

Cambrian explosion

Answer to Question 2

ozone layer
ozone screen

[aabwk4]

Thanks for the timely response, appreciate it

[adf223]

Excellent