VOLUME 33, NO. 2, FEBRUARY, 1956
THE ELEMENTARY COMPOSITION OF THE EARTH ISAAC ASIMOV Boston University School of Medicine. Boston, Massachusetts
IK .L previous communication,' the author prepared t,ables giving the elementary composition of the earth's rrubt by atom number as well as by weight, in an effort t,o show how this altered the usual conception of the reht,ive frequency of occurrence of the different elements. The author has since 'ome across a table2 estimating the elementary composition of the earth a s a whole (see Table l),using the usual unit, i. e., per cent hy weight. It will be seen that iron is in first place by a good margin. This is not unexpected in view of the earth's well known "iron core." Nevertheless it would be over-hasty to suppose that oxygen, so predominant in the earth's crust, mnet be Anr~ov,I., J. CHEM.EDUC31, 70 (1954). Given in WEAYER,E. C. A Y D L. S. FOSTER,"Chemistry fat. Our Times," McGrarv-Hill Book Co., Inc., New York, 1954. The tshle is there stated to have been prepared by H. S. Wsshington of the Geophysical Lahoratovp, Washington, D. C.
satisfied ~\.ithsecond place once the iron core is counted in. After all, it must be remembered that the individual iron atom is 3.5 times as massive as the oxygen atom. If the elements are counted not by weight but by atom numbers, Tahle 2 is the result. I t can now be seen that there are more atoms of oxygen in the entire earth, iron core and all, than any other. I n fact, there are almost as many atoms of oxygen in the earth, iron core and all, as all other kinds of atoms combined. A final note: The ratio of neutrons to protons in the individual elements, as naturally occurring, can readily be calculated when the frequency and mass number of the isotopes of each element are knomn. Taking a weighted average of these ratios for the elements predominating in the earth, it can be calculat,ed that the number of neutrons in the earth is 1.064 times the number of protons.
TABLE 1 Elementary Composition of t h e Earth by Weight
TABLE 2 Elementary Composition of t h e E a r t h by Atom Number
I
2
Element
Iron Oxygen Silicon Magnesium Kickel Citlcium Aluminum Sulfur Sodium Cobalt Chromium Poti~ssium Phosphorus Manganese Carbon
G i n m per la thousand grams
Element
Oxygen Iron Silicon Magnesium Aluminum Calcium Nickel Sulfur Sodium Cobalt Chromium Potsssium Phosphorus Carbon Manganese Titanium
Atoms aer ten thousand atoms
4 1
JOURNAL OF CHEMICAL EDUCATION
68
NEW
/?ER/OD/C n6L.E BASED ON STAWTY
OF ATOMC
ORBITALS
from above - - - - - a d 4 4s2 -----3d94 s 2 ----- 4dJ 5s2 - - - - - 4 d 4 5s' -----4 d 6 5s' - - - - - 4 d 7 5s2 - - - - -4 dB 5s2 ---- -4d9 5s2 ---- - -4d5 5s' - - - - - 5 d 7 6s2 ----- 5d8 6s2 ------5d9 6 s2
