Throughout this site and others, these units are used to denote energy yield in large quantities due to asteroids, volcanoes, explosives etc. One ton of TNT is equal to 4184,000,000 joules… and multiples of such for higher energies. http://upload.wikimedia.org/wikipedia/commons/thumb/a/ad/Sailor_Hat_Shot.jpg/170px-Sailor_Hat_Shot.jpg