Without chlorine, life as we know it could not exist. The average adult human has about 1/5 of a pound of chlorine in their body. One way to think about this is examining table salt. Table salt is half negatively charged chlorine and half positively charged sodium. It’s important for a living thing to balance its charge and one of the easiest ways to add negative charge is through chlorine. Also chlorine is important in forming hydrochloric acid which makes the stomach very acidic. The transfer of chlorine in and out of cells plays many important roles in an organism’s health. An example of this importance is the disease cystic fibrosis in which a mutation to a channel that transports chlorine causes it to not work properly.This small change leads to a number of serious issues such as difficulty breathing and poor growth.

Though there are many other examples of how chlorine is used; it is most notable as part of bleach which can be used for keeping pools clean and killing bacteria. Chlorine also plays an important role in making some plastics such as PVC (polyvinyl chloride). On a more cosmic note, the way elements are made in the center of stars and in supernovas leads to elements we see today and there would be no clear way for this process to skip chlorine. Chlorine like many elements, plays an important role in life as well as the nonliving natural world. It would really be impossible to imagine the world without it.

Chlorine is the anion responsible for most salts, so it is extremely important. If chlorine weren't there, then the elements that make salts with chlorine (mainly sodium, magnesium, potassium, and calcium) would have to react with something else, probably oxygen. Combining these metals with oxygen results in salts with very different properties, many of them insoluble in water. Without Chlorine, life as we know it would probably not be possible.

Chlorine is a very common element and important in nature and also for man-made materials and technology. Chlorine compounds with sodium to make salt (NaCl, called 'sodium chloride'), which is the most common chlorine compound in nature and is abundant in the salty oceans and the Earth's crust. Without chlorine, sodium would try to find an alternative counter-ion when dissolved in water, for example, iodine or bicarbonate.

When animals consume salt, we use the chloride ions, which are negatively charged, to maintain the charge balance in our blood and other fluids. Without chlorine, our bodies would have had to evolve a different mechanism for maintaining charge balance.

I mentioned that chlorine is also important for technology. Because chlorine is a strong oxidizing agent, it's very useful in chemical processes to make synthetic materials like plastics. Without chlorine, scientists and engineers would have to find another way to make these materials and end products.