A) The climate first warmed, then cooled, and most recently became variable.
B) The climate underwent a constant cooling trend, with decreasing variability.
C) The climate underwent a constant warming trend, with some recent variability.
D) The average climate did not change but the variability went down.

A) Because Pangaea was so large, it probably had cold winter weather, like Asia does today.
B) Because Pangaea was so large, it facilitated the circulation of water from the tropics to the poles.
C) Cold areas of the world today, such as Alaska, were always cold.
D) Europe was never tropical.

A) isotopes decay at a known rate.
B) older layers are deeper than younger layers.
C) when rocks are formed, chemical signatures determine how long they will last.
D) when rocks are formed, their chemical configuration never changes.