Earth's Cycles

As well as plate tectonics, there is other evidence that the earth is a dynamic system. This comes in the recognition that there are three main cycles on the earth: the atmospheric, water, and rock cycles. These cycles result from two main facts about the Earth:

and also

On a local scale this is illustrated dramatically in the lesson of Lake Victoria, a large lake in Africa. For hundreds of years this lake flourished and provided sustenance to many people living nearby. Then, in an effort to increase tourism, large pike were introduced into the lake as sport fish. These pike ate the smaller fish, which up until then had been responsible for keeping the oxygen-depleting weeds in the lake under control. These weeds then multiplied until the lake essentially died. Furthermore, the people living around the lake started to fish for the larger pike, as the smaller fish were scarce, and subsequently had to use the surrounding timber as fuel for fires to smoke and preserve the pike. This led to a destruction of the surrounding forests, and a corresponding increase in erosion around the lake. Today efforts are being made to restore Lake Victoria, but this shows how a single change in a closed system can dramatically affect the whole system.