There is no exact reason why the solar system is arranged the way it is. But humans have discovered certain laws of nature that seem to keep the solar system in its present pattern. Earth, like the other planets, follows its path, or orbit, around the sun. But there are two main types of theories. First theory suggests that the formation of the planets was a part of the gradual changes in the sun from whirling masses of hot the gas to its present size and brilliance.
Second theory is based on the idea that at some time there was a collision between the sun and another star passing nearby which resulted in pieces of the sun which began to revolve around the sun at different distances. These are now called as planets. So the solar system remains as it is because certain laws of nature maintain the relationship of the sun and the planets.