A cross-section of an extremely tiny carbon sphere. It was taken with a transmission electron microscope and has color added. Scientists study nano-structures because they have a strong influence on a material's chemical and physical properties - which are important to know when designing new technologies. Carbon is a chemical element with symbol C and atomic number 6. It is nonmetallic and tetravalent the 15th most abundant element in the Earth's crust, and the fourth most abundant element in the universe by mass after hydrogen, helium, and oxygen. It is present in all forms of carbon-based life, and in the human body carbon is the second most abundant element by mass (about 18.5%) after oxygen. Nanotechnology (nanotech) is the manipulation of matter on an atomic, molecular, and supramolecular scale.