The thin outer layer of earth, called the crust, contains only 0.50 percent of earth's total mass and yet is the source of almost all the elements (the atmosphere provides elements such as oxygen, nitrogen, and a few other gases). silicon (si) is the second most abundant element in earth's crust (27.2 percent by mass). calculate the mass of silicon in kilograms in earth's crust (mass of earth 5.9 x 10^21 tons; 1 ton= 2000lb; 1lb =453.6 g).