Global Change in the earth system Part 2

Geologists study Earth's climate history by deciphering clues preserved in the geologic record. In the northern hemisphere, which of the following observations would you expect to see if the climate were colder in the geologic past than it is today?

Choose one or more:
A. higher 18O/16O ratios in plankton shells
B. lower 18O/16O ratios in plankton shells
C. a more northerly distribution of spruce forests
D. spruce pollen being more abundant than grass pollen
E. a more southerly distribution of spruce forests
F. grass pollen being more abundant than spruce pollen