How much matter is there in earth?

Elements are defined by their atomic nucleus, the core of the atom, consisting of neutral neutrons and positive protons. The thing that makes two elements different is the number of protons. For example Hydrogen has 1 proton, Oxygen has 8 and Gold has 79. If you have two elements with different numbers of neutrons, they are called isotopes of that element. In principle you can create a new element by smashing together a bunch of protons to create a nucleus, but some combinations are much more stable than others. Therefore the vast, majority of the matter in the universe consists of the first 92 elements of the Periodic Table (after Uranium, which has 92 protons and is therefore element number 92, they are all radioactive and no higher numbered element occurs naturally on Earth). Most of that matter again consists of Hydrogen with one proton (ca. 75%) and Helium with two (ca. 23%) with all other elements sharing the remaining 2%.