In creating a model of our living planet, scientists need to consider four major Earth systems. Briefly describe these four systems, and then explain why it is difficult to study these systems individually.

Plants transfer carbon in the carbon cycle a. through assimilation of carbon from the soil. b. when carbon transpires from their stomatae. c. when they are eaten by animals. d. through fixation of carbon in the soil.plants transfer carbon in the carbon cycle a. through assimilation of carbon from the soil. b. when carbon transpires from their stomatae. c. when they are eaten by animals. d. through fixation of carbon in the soil.