Competition is central to the theory of natural selection. why does competition occur?

Competition occurs basically because of the limited supply of items. For example, two animals compete for the same food basically because there is no enough food for the two of them. Had there been enough, they will just go on their ways. The same also is happening for the shelter, territory, or even partners. 

It seems that you have missed the necessary options for us to answer this question, but anyway, here is the answer. Competition is central to the theory of natural selection. Competition occurs because organisms typically produce too many offspring, and resources are limited. Hope this answers your question.

They both determine the exact age of rocks.

Ibelieve the answer is relative humidity  because it makes more sense that way. solar flares usually occur in space it doesn't affect the earth, well it could but it wont make a significant damage.  latitude is land it doesnt do anything. prevailing winds, i dont know the correct meaning for this but i doubt that affects the land so it has to be relative humidity.