How many elements is the earth made of?
The periodic table goes up to 118, but many of the higher atomic numbers are synthetic, are only made in the lab and not found in nature, even in trace amounts. The highest atomic number element found in nature is trace amounts of Plutonium. It is found within Uranium deposits from natural fission and some primordial Plutonium in the crust left over from a supernova that added material into the molecular cloud the solar system was formed from.
The accounting above is in NUMBER even trace amounts of very rare elements are counted. The WHOLE earth (not the crust) is estimated to be mostly by MASS iron, oxygen, silicon, magnesium and nickle; by NUMBER oxygen magnesium silicon, iron and aluminum (top 5). Note that when combined elements like oxygen, magnesium, silicon, and iron tend to make ROCK.
Wiki has a GREAT article about the abundances which include the earth's crust, the WHOLE earth, the solar system, the Milkyway galaxy and the universe.