Subsequent research indicates that the same careful balance and the means to maintain it exist for carbon and nitrogen in Earth's oceans. As on the continents, intricate processes at work in the oceans take nitrogen out and put it back in, and these processes are directly connected with the flow of carbon into and out of the environment. If these processes of depletion and replenishment are out of balance, life cannot survive. Further investigation reveals that this crucial nitrogen cycle, on which the carbon cycle depends, relies critically on oceanic oxygen cycles. Planetary physicist John Lewis, whose book Physics and Chemistry of the Solar System I highly recommend, also explains the fine-tuning of chlorine for life.
Chlorine does much more than purify swimming pool water.
It plays a significant role in determining erosion rates, several metabolic processes, and the acidity of lakes and rivers. As with nitrogen, sulfur, carbon, oxygen, and other life-essential elements, chlorine must be present in just the right amounts in just the right places at just the right times.