Why do we believe the Cambrian explosion occurred so suddenly? ...

[altibaby]

Why do we believe the Cambrian explosion occurred so suddenly?
 
  A) oxygen concentrations reached critical levels necessary to support more complex life
  B) organisms became sufficiently complex that more diversity became possible
  C) climate change due the end of the last snowball Earth phase
  D) all of these

Question 2

In the outer regions of the solar nebula where temperatures were low,
 
  A) only rock and iron could condense
  B) only hydrogen compounds could condense as ices
  C) hydrogen and helium gases were able to condense
  D) in addition to rock and iron, hydrogen compounds also condensed as ices

[recede]

Answer to Question 1

D

Answer to Question 2

D

[altibaby]

Thanks for the timely response, appreciate it

[ttt030911]

Great answer, keep it coming