Question

What is the lightest and heviest substance on earth

Answer 1

carbon aerogel is the lightest by, it weighs 0.16milligram
osmium is the heaviest

Answer 2

The heaviest known object is the Laniakea supercluster, which is about 1017 times the mass of the sun. The light objects, besides massless particles, are neutrinos, which have a mass less than a millionth that of an electron, but it is not known exactly what it is. If axions exist, they are likely even lighter, about a trillionth of an electron mass.