The atomic structure of carbon, more specifically naturally occurring diamond, is neatly stacked in a cuboid shape. Carbon nanotubes use carbon but instead stack their atoms in a hexagonal shape. The result is a material which weighs virtually nothing, yet is stronger than any material known upon Earth, including poly-paraphenylene terephthalamide, more commonly referred to as “Kevlar”, zylon, and titanium. Some scientists have argued that carbon nanotubes will most likely be the strongest substance in the known universe and that nothing will ever have the ability to surpass its strength. Carbon nanotubes have a strength of 200 gigapascals; to provide frame of reference, the strongest materials known to civilization have a strength of approximately 5 gigapascals. 1 gigapascal, which is commonly abbreviated as “GPa”, is equal to 1,000,000,000 (1 billion) pascals, and 1 pascal, which is commonly abbreviated as “Pa”, is the SI unit for pressure defined as “1 newton per 1 square meter”. If a space elevator ribbon made of carbon nanotubes stretching 100 kilometers were ever to break (e.g. the counterweight above breaking), it would gently float down to Earth because it would only weighs 7 kilograms per every 1 kilometre of length