1. the presence of 7.4% (by weight) of the element ni in the earth's core is indicated by geophysical (seismic data). the mass of the earth is 5.97 x 1027g; the mass of the core is: 1.94 x 1027g; the mass of the mantle is: 4.02 x 1027g. a. the volume of the earth's crust is 1.02 x 1010km3; mean crustal density is 2.8g/cm3; and mean concentration of ni in the crust is 75 parts per million (ppm) by weight. how many grams of ni are in the earth's crust? explain, you.