Understanding the geosphere’s chemical composition starts with the basics-the chemical elements. A chemical element is a substance that can’t be broken down chemically into other substances. There are about 90 naturally occurring elements, each with a unique name and chemical symbol. You are very familiar with at least one element, oxygen (O), that your body needs for respiration. Although you haven’t actually seen oxygen, take a deep breath and think about it. Luckily for us, the atmosphere readily supplies the oxygen that we need to live.