The model you see here is very similar to illustrations you will find in many textbooks. It shows the sizes of the different stores of carbon (e.g. 600 Gigatonnes of carbon in the atmosphere as shown by the number inside the cloud) and the rates at which carbon moves between the stores (e.g. 74 Gigatonnes of carbon moves from the atmosphere into the oceans every year as shown by the black arrow). The difference is, with this model, you can change things. It’s not a static illustration of the present Earth but a dynamic model of possible Earth’s. Play with it using the Simulation item on the Carbon Cycle menu to see what happens but first look at the Tutorial item on the same menu.