When atmospheric CO2 concentrations reach ________, scientists ...

[jlmhmf]

When atmospheric CO2 concentrations reach ________, scientists believe a possible climatic threshold in which Earth systems could transition in a chaotic mode will be reached.
 
  A) 300 ppm B) 350 ppm C) 400 ppm D) 450 ppm E) 500 ppm

Question 2

Which of the following is the correct sequence from the surface to the bedrock in a typical soil horizon.
 
  A) O, A, E, B, C B) C, B, E, A, O C) S, O, I, L D) O, E, C, B, A E) A, B, C, O, R

[softEldritch]

Answer to Question 1

D

Answer to Question 2

A