EVOLUTION OF T H E ODD-NUMBERED ELEMENTS BY W. V. HOWARD
Introduction A reading of Aston’s “Isotopes” and various papers by Harkins,’ and Clarke led the writer to endeavor to predict the isotopes of those elements which had not yet been examined, and also to try to find out whether or not there was some sort of serial arrangement which might possibly indicate a process of evolution. Accordingly, he plotted the isotopes of the evennumbered elements which had been reported in Aston’s book and found that there seemed to be definite series of elements whose mass numbers differed by four, and whose atomic numbers differed by two. That is, there were series whose mass numbers could be expressed by one or other of the following formulae*:M = z?$ 4X or M = zS 4X 2,
+
+
+
where 34 is the atomic weight, K is the atomic number and X is an integer between o and 13. (See Fig. I . ) I n the original graph, the relationships between the radioactive elements differed from those between the nonradio-active elements, so they were omitted. Also, the elements below carbon were omitted because the relationships between these seemed to be different from those in the elements occurring above carbon.
Isotopes of Odd-Numbered Elements I n dealing with the odd-numbered elements, it was found that the same serial arrangement prevailed, but the surprising fact was, that, with very few exceptions, every even-numbered element was preceded by an odd-numbered element whose isotopes had mass-numbers which were less by one than one or the other or both of the two lowest isotopes of the even-numbered element. (See Fig. 2 ) . Odd Mass Numbers in Isotopes of Even-Numbered Elements Although no odd-numbered element (above oxygen and below lead) has an even mass-number, several even-numbered elements have odd-numbered isotopes. These include zinc, selenium, krypton, tin, xenon and mercury. Of these zinc, krypton and mercury definitely end one or two series whose members satisfy the formulae referred to above for a given value of X and it is probable that xenon does also. Also there is some irregularity in connection with the odd-numbered elements preceding krypton and xenon, and therefore selenium and tin may also end series. Chiefly W. D. Harkins: “The Evolution of the Elements”, J. Am. Chem. SOC., 39, 864 (1917) and F. W. Clarke: “The Evolution and Disintegration of Matter”, U. S.Geol. Survey, Prof. Paper 132-D (1924). * The values and f i 2 are the same as the isotopic numbers of Harkins: Phil. h k . , ( 6 ) 42, 305-339 (1921).
+
*
W. V. HOWARD
1726
3 2
i 0
t-
< ao-yi-
dl
/
l
10
o
o
-
t
4-
la
/
C 3 0 -AT?-
10 I
'
/
H:
57
0-
I-
p ,r qk
/
80
70
r
-s e k r -
/60-
-
ATOMIC NUMBERS PIC. I
Isotopes of even-numbered elements as reported by Aston
EVOLUTION OF T H E ODD-KUMBERED ELEMENTS
' P 20I
CI
u z 0
I-
U
20-p0 I1 O
C
to
He 5.
0
80--&%
B5
40
ATOMIC NUMBERS
FIG.2 Isotopes of elements reported by Aston
1728
W. V. HOWARD
Relations between Elements The following rules may be formulated for the elements between carbon and polonium (except nitrogen).' (a) The isotopes of the even-numbered elements form two groups of series of which one group conforms to the equation M=zN+4X and the other to the equation M = 2N 4X 2, where hi is the mass number of the isotope, N the atomic number of the element and X any whole number between o and 1 1 , or between o and 13 if the radio-active elements are included. (b) Each series corresponding to any given value of X in one or other of the two equations is terminated by an element which has an odd-numbered isotope, and in some cases two odd-numbered isotopes. (c) The odd-numbered isotopes of the even-numbered elements may lie immediately above the lowest and second lowest even-numbered isotopes, or above either of these, but do not occupy a higher position in the list of isotopes of any element.2 (d) The elements whose lower isotopes terminate one or two series have higher isotopes which begin one or two others. As an obvious corollary it may be stated that the even-numbered elements which contain odd isotopes have a larger number of even isotopes than neighboring even numbered elements which have no odd isotopes. (e) Few elements have more than five even-numbered isotopes. (f) The above rules do not hold in their entirety for the two series in which X = 0. (9) No odd-numbered element has more than two isotopes. (h) No odd-numbered element has an isotope with an even mass number. (i) No odd-numbered element has an isotope whose mass number is the same as that of any isotope of any other element, odd or even. (j) If an odd-numbered element has two isotopes, the following evennumbered element cannot have more than one odd isotope. (k) The isotopes of all odd-numbered elements have a mass number which is less by one than one or other or both of the two lowest isotopes of the even-numbered element immediately following. If the isotopic numbers of Harkins are used in place of the values 4X and 4X z i t will be found that most of the rules as stated above have been anticipated by Harkins. The isotopes predicted by Harkins3 vary radically from those of the writer owing to the fact that the relations noted in rule (k) have not been stated by Harkins. I n several cases certain elements are believed to end series, and will thus have odd isotopes, in spite of the fact that the following even-numbered ele-
+
+
+
Russell's rules are the same as these in many respects (Nature, 112, 588 (1923) ). This, of course, cannot apply to the radioactive elements. a J. Franklin Inst., 195, jjI-573 (1923).
EVOLUTION OF THE ODD-NUMBERED ELEMENTS
1729
ments have isotopes in the same series. These latter elements which include krypton, xenon, and tin do not follow the rule regarding the distribution of odd isotopes. Thus the odd isotope of krypton is found above the third even isotope rather than the second, xenon has two even isotopes followed by alternating even and odd, and tin has no fewer than four odd isotopes which are placed above the second, third, fourth and fifth even isotopes. I n these cases, it is believed that the preceding elements do not present the same degree of instability as do the elements which ordinarily terminate series. These apparent exceptions to the rules given above, indicate the possibility that further examination may disclose the presence of still others. This will necessitate a modification of the rules, but will not affect the relations existing between the odd numbered elements and the following even numbered elements, except insofar as the position of the related isotopes is concerned. I n the cases of krypton, xenon and tin, the preceding odd-numbered elements have positions which are not in accord with rule (k) bromine is related to the second and third isotopes of krypton, iodine to the third isotope of xenon and, from its atomic weight, indium is believed to be related to the third lowest isotopes of tin, in spite of the fact that Aston has found an isotope of tin which has the same mass number. Chlorine has two isotopes C1 3 5 and C1 37. There is a corresponding isotope of argon A 36, but no A 38, nor is there a Ca 43 following K 41. In the case of argon, it may be stated that the inert gases appear to present exceptions to many of these rules-vide krypton and xenon above.
Prediction of Unknown Isotopes It was found that these rules were not sufficient to permit the prediction of the isotopes of the other elements, chiefly because no rule could be formulated which would indicate which elements should terminate series. 4X were terminated as follows:Certain series in the group &I = zN Series o (i.e X = 0) is terminated by calcium, series I by zinc, series z by krypton, series 3 by cadmium, series 4 by tin and series 5 by xenon, and it is probable that series I O is terminated by polonium, but the position of the elements terminating series 6, 7 , 8, and 9 can not be determined as most of 4X z them fall within the rare earth group. Similarly in the RI = Z N group, series o is terminated by nickel, series I by selenium, 3 by cadmium and 9 by mercury. Series 4 is believed to be terminated by tellurium by analogy with selenium. Also by analogy with nickel, i t is possible to assume that series z is terminated by ruthenium and series 8 by osmium. Polonium is believed to terminate series I O , leaving series 5 , 6, and 7 to end somewhere within the rare earth group. A. S. Russell has endeavoured to predict the mass numbers of the isotopes of the elements2 and the writer’s efforts resulted in such close agreement with his that an attempt was made to try to fit Russell’s results to the rules already formulated. According to Russell, the following ele-
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2 A . S. Russell: Phil. Mag., 47, 1121-1140;48, 365-378 (1924).
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W. V. HOWARD
FIQ.3 Even-numbered elements Isotopes of even-numbered elements between Carbon and Polonium
EVOLUTION O F THE ODD-NUMBERED ELEMENTS
1731
ments lying between xenon and mercury have at least one odd isotope, neodymium, gadolinium, dysprosium, ytterbium, hafnium and osmium. Using the mass numbers given by Russell for the isotopes of these elements, it is possible to show that all except hafnium both end and begin series so that
P
ne
0
A TONIC NUfl0€RJ FIG.4 Odd and even-numbered elements Isotopes of all non-radioactive elements above carbon
the difficulty presented by the rare earth group is solved; except for the value Hf 179. With these additional data the completed tables were prepared. (Figs. 3 and 4.) These tables differ from the results of Aston in very few cases, as an attempt was made to begin with Xston's results and to reason from them. In some cases questionable valued found by Aston were omitted. Thus Ti
W. V. HOWARD
I732
50 is not believed to exist, for if i t does then we should expect that there would be an odd-numbered isotope of titanium and also one with a value Ti 44. (See rule (d) above.) On the other hand, the experimentally doubtful Zn 67 is believed to exist since zinc follows this rule (d) in other respects. Aston found no value Sr 90, but i t is believed that this exists in order to 4X 2 (X = 3 ) which maintain the continuity of the series M = zN begins with Se 86 and ends with Cd I IO. Owing to the different methods used in calculation by the writer and by Russell, there is a little more disagreement between our results. Some of Russell’s values (such as M n 5 3 , Co j j ) do not agree with experimental results and are therefore omitted from the tables. With the exception of the value Hf I 79 none of the other points of disagreement are of great importance. Most of them are due to the fact that the writer has considered that the series are continuous and he has been forced to add one or more isotopes to some elements. These, if present a t all, are not abundant. If, however, Hf 179 exists, then by rule (d) hafnium must end a series. If it does, then Hf 176 must also exist. If it ends a series, then by the same rule, it must begin one. If i t begins one, the values Hf 184 and W 188 are necessary. I n other words the writer is either forced to disagree once with Russell and omit the value Hf 179, or to add three other values which Russell does not admit, and which are, indeed, unnecessary so far as the writer’s hypothesis is concerned.
+
+
Evolution of the Elements The first elements to form were the even-numbered elements between carbon and nickel, together with hydrogen and helium. These last elements appear to be the material from which all elements are derived, although the above outline of the relations between the elements does not indicate the precise manner in which the more complex elements were built up. Between carbon and calcium the elements have mass-numbers which either equal twice the atomic number or are equal to tnTice the atomic number plus two (Le. X = 0). I n the latter series there are many gaps, thus there is no representative in this series of carbon, oxygen, argon, or calcium. It would appear, then, that the isotopes of the elements which belong in the M = 2 s 4X 2 series (X = 0) developed from the lower isotopes which lie in the hl = 2 N 4 X series (X = 0). The atomic weights of the elements which lie between carbon and chromium show that the most abundant isotope of those elements which have more than one isotope is the one lying in the M = 2K 4 X series. Thus the atomic weight of neon is 2 0 . 2 (isotopes 20 and 2 2 ) , that of magnesium is 2 4 . 3 2 (isotopes 2 6 , z j , and 2 6 )of silicon 2 8 . 0 7 (isotopes 2 8 , 29, and 3 0 . ) The statement that evolution began with the formation of the evennumbered elements from carbon to nickel, with hydrogen and helium is based on our knowledge of the meteorites and the deductions that have been made from this knowledge as regards the earth. Astrophysics provides much confirmatory evidence. As later evolution followed a somewhat dif-
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+
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+
EVOLUTION O F THE ODD-NUMBERED ELEMENTS
I733
ferent course although the same general principles were involved, i t is to be expected that the elements below nickel would have different characteristics from those above. Thus the series are not continuous below nickel, and unstable conditions seem to have caused magnesium, silicon, and sulphur to form an odd-numbered isotope. Following the formation of these elements,the evolutionary processes continued in three ways, namely, the formation of the higher even-numbered elements, the odd-numbered elements and the elements between nitrogen and lithium. The even-numbered elements whose mass numbers are higher than those of nickel may have been formed by the addition of either helium atoms or of neutrons to atoms already formed. When helium atoms are added, the properties of the atom are changed and a new element is formed. The new element, however, is a member of the same series as the old. Thus in the 4X (X = z ) , 30 Zn 68 is the first member. On the addition series M = zN of a helium atom 3 2 Ge 7 2 is formed; then 34 Se 76 and finally 36 Kr 80. The addition of helium atoms cannot continue indefinitely and as the atomic weight increases the elements become unstable unless more than two negative charges are added to the nucleus for every four protons. In such a case neutrons are added, usually in pairs. If, however, the degree of instability possessed by end-members of a series is reached, neutrons may be added singly although this addition of single neutrons will not continue after the formation of the third even isotope, because of the increasing stability of the atom. The elements whose lower isotopes and series require the addition of a larger number of neutrons than do the others for precisely the same reason that they end series; namely because they are more unstable than those elements which immediately precede them in the periodic table. They therefore add enough neutrons to enable them to begin new series. From this it can be seen that the lower isotopes of any element will be less stable than the higher ones. It may, therefore, be expected that the lowest isotopes are present in less abundance than the second lowest, which, in turn, will not be as abundant as the third lowest. The higher isotopes, on the other hand, are formed as a result of the instability of the lower ones and the quantity so formed may be very small. The odd-numbered elements were formed by a process of disintegration of the even-numbered elements, whereby one or both of the two lowest (and therefore the least stable) isotopes lost one positive charge from the nucleus and one electron. This proton and electron formed a hydrogen atom which may have gone into the formation of higher isotopes of even-numbered elements or may have remained as a hydrogen atom which later became a hydrogen molecule. Since the valence of the odd-numbered elements is less than that of the even-numbered elements immediately following, it follows that for every two atoms of an odd-numbered element formed two atoms of hydrogen and one of oxygen are given off. Applying these principles of evolution and disintegration to the elements below carbon, a scheme may be outlined which can account for their irregularities but this scheme is hardly more than a guess, probably a very poor
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IT31
W . T. HOWARD
one, a t that. If it be assumed that nitrogen was formed in the ordinary way by some such combination as three helium and two hydrogen atoms, and then, by a process of disintegration, it lost first one helium atom and then another, ~ B I and O 3Li6 could be formed. Also ~ B I could I be formed by the loss of one proton and one electron froiii carbon, and this would give off one helium atom forming 3Lij. 4Re9 is formed from ~ B I O by the loss of one proton and one electron. Thus the elements below nitrogen reverse the usual plan, and the odd-numbered elements act in the same way as do the even-numbered elements above nitrogen and vice-versa. So far the hypothesis has been stated with as little detail as possible so as to present its major features. Saturally, since it deals with the very fundamental processes of chemical and geological change it is necessary to inquire further into it In order that we may see whether or not it will fit observed facts and furthermore whether or not it mill solve existing difficulties. Until it can be shown that the hypothesis can be applied it would seem of little avail to consider further a revolutionary idea that is based solely on certain numerical relations and predictions based on these relations.
Experimental Evidence Rutherford and Chadwick bombarded certain elements of low atomic number with a-particles and obtained hydrogen. As a result of these experiments, i t was found that the hydrogen atoms driven off from elements of even atomic number had a shorter range than those driven off from elements of odd atomic number indicating that the even-numbered elements were more stable than the odd, insofar as this particular bombardment was concerned. This did not, however, indicate anything else, in the writer's opinion, as regards the stability of the atoms except that they differed from one another. The process, if i t exists, whereby odd-numbered elements are formed from even, is not a bombardment of the elements -ivithin the crust by alpha-particles but a natural disintegration which is analogous to radioactive disintegration though quite different from i t in detail. Perrin' suggests that the following reaction takes place. A1 a-particle-H = Si This equation in terms of atomic weights may be expressed:
+
2;
+4 -
I
= 30
I
= 14.
and in terms of atomic numbers 13 f z -
If, however this process is applied to such an element as manganese, we have the following results: Atomic weights:- j j 4 - I = 58 (nickel) z - I = 26 (iron) Atomic numbers:- 2 5 I n other words, if an odd-numbered element is not followed by an evennumbered element with an isotope having a mass-number which is greater by three than that of the odd-numbered element, this reaction can not cake place in this way.
+ +
'Quoted by Rutherford: Sature, 115, 493 (1925).
EVOLUTIOS O F THE ODD-XUMBERED ELEJIESTG
1735
Gold derived from Mercury The derivation of gold from mercury which was reported by &liethe’ and later by Sagaoka2 has a considerable bearing on this hypothesis. Although later tests, using RIiethe’s methods, failed to achieve positive results, the writer is informed by Dr. A. L. Day’ that Nagaoka’s work has been resubmitted to careful scrutiny and that tests on mercury previously purified by an independent investigator of his process gave a positive result. The suggestion of Stumpf? that the isotope of mercury 197 originally reported by Xstonj was really gold is of interest. The fact that extremely careful refinement is necessary to remove all traces of gold from mercury would tend to indicate some process whereby gold was actually being formed from mercury, and the fact that mercury which has been refined with especial care shows no trace of gold might indicate that the process of disintegration is very slow. The writer would be very much interested in seeing the results of experiments in which mercury, refined to such a degree that it contained no trace of gold, was allowed to stand for a year or more before being retested in order to see whether or not gold could be obtained. I n case this transmutation actually takes place it is probably the isotope of mercury 198 which breaks down to form gold 197. I n that event, if enough gold were found to make any appreciable effect upon the mercury, it would be interesting to find out whether or not the atomic veight of the mercury had actually increased and also whether or not the isotope 198 was less abundant than before the disintegration was effected. The successful performance of this experiment would indicate to some extent the correctness of the writer’s hypothesis, as it is to be expected that elements of higher atomic weight would give better results than those of lower atomic weight. The formation of gold from mercury would be more easily demonstrated than any other such change except possibly the formation of thallium from lead. Piutti and Boggio-Lera6 are reported by Xature’ as stating that the view that mercury may undergo spontaneous transmutation into gold is suggested by the invariable presence of gold in commercial mercury. The transmutation of lead t o mercury and thallium was reported by A. Smits8and in endeavoring to explain both the transmutation of mercury to gold and of lead to thallium, Davies and Hortong point out that “the change might conceivably be effected either by the entry of an electron into, or by the removal of a proton from, the nucleus of the mercury atom. The same alternatives present themselves in regard to the transformation of lead (82) into thallium (81)” Sature, 114, 197 (1924‘1. Nature, 116, 9 j (192jj. 3 Personal communication. h-ature, 115, 172 (1925). “Isotopes” (1924). Later determinations have shovn that Hg 197 does not exist. E Rend. Accad. Sci. Fis. Matem. (Xaples) Sept-Dec. (192j). 117, 604 (1926). * Xature, 117, 1 3 (1926:. Sature, 117, I j Z (1926). 1
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W. V. HOWARD
I n this connection it might be pointed out that the transmutation of elements below lead cannot be due to radioactive processes, and mercury 198 and gold 197 cannot simply be lower members of the radioactive series. It is true that Hg 204 might be formed as a result of the radioactive disintegration of thorium lead, but from this point disintegration would have to proceed from one isotope of mercury to another, something that might conceivably happen if the higher isotopes were derived from the lower, and then follow a third method whereby Au 197 could be formed. Thus there would be two new modes of disintegration besides the two radioactive methods which would seem entirely unlikely, and it would seem impossible to derive gold from lead by any single process.
The Composition of Meteorites, etc. The great preponderance of even-numbered elements over odd-numbered elements in the meteorites has already been pointed out by Harkins' and others. This was regarded by Harkins as evidence of the greater stability of the even-numbered elements, but it would seem more probable that it is evidence that, normally, only the even-numbered elements would form and that the odd-numbered elements are formed a t a later time. Harkins, in the same articles, pointed out that wherever an odd-numbered element was a t all abundant, the neighboring even-numbered elements were still more abundant. This might be believed to be indicative of the disintegration of the latter to form the former, especially if the relation between the odd-numbered elements and the lowest isotopes of the even-numbered elements be considered. The only odd-numbered elements found in any abundance in the iron meteorites are cobalt and phosphorus and both nickel and sulphur are also present, although sulphur is not so abundant as phosphorus. In many meteoric irons a considerable amount of hydrogen has been found which substantiates the idea that the cobalt may have been formed by the disintegration of nickel with the formation of hydrogen. I n the meteoric stones, cobalt, aluminum, sodium, potassium, and phosphorus are all present, but in no case in the average composition does any one of these elements occur in quantities greater than 10% of the even numbered elements immediately following. In the achondritic meteorites, the same odd-numbered elements are present with manganese in addition, and here too, none of them are more than onetenth as abundant as the even-numbered elements immediately following with the exception of aluminum which amounts to less than one-seventh of the silicon present. I n Clarke's paper on the evolution and disintegration of matter2he points out that the Class B stars contain besides helium and hydrogen, silicon, oxygen and nitrogen, and that in the class A stars magnesium, calcium, iron and titanium are beginning to appear. With the exception of nitrogen, these 'Harkins: J. Am. Chem. SOC., 39, 877 (1917);Phil. Mag. ( 6 ) , 42,305-339 (1921). ZU. S. Geol. Survey, Prof. Paper, 132 D (1924).
EVOLUTION OF THE ODD-NUMBERED ELEMENTS
I737
elements together with carbon, chromium and nickel, all of which are found in the meteoric irons, make up the two series in which X = o and seem to be the elements from which all others are derived. Nitrogen has been referred to as the possible source of the lightest elements, except helium and hydrogen. The two additional members of the o series, argon and neon, do not appear to fit into the general scheme’ unless, being gases a t normal temperatures, they were too volatile when formed to be retained by the parent mass and were dissipated into space. The relative abundance of elements in the Sun’s atmosphere is given by Washington* as follows : calcium, iron, hydrogen, sodium, nickel, magnesium, cobalt, silicon, aluminum, titantium, chromium, strontium, manganese, vanadium, barium, carbon. Of the odd-numbered elements in this list, exclusive of hydrogen, sodium is more abundant than magnesium, but all of the others are less abundant than their possible source-elements. Aluminum is very close to silicon and this gives rise to the suggestion that sodium is the easiest of all the odd-numbered elements to form, with aluminum next. As a matter of fact, potassium is also abundant in the sun’s atmosphere of which it forms, together with hydrogen, the outer layer. Thus, in the sun’s atmosphere, the most abundant odd-numbered elements are identical with the most abundant odd-numbered elements on the earth’s crust and, in addition, the hydrogen formed as a result of the disintegration of the even-numbered elements is also present in great abundance. This would seem to be more than a mere coincidence.
Association of Elements within the Earth In a few cases odd-numbered elements are found associated with the evennumbered elements from which they are believed to be derived. Examples of this association include copper and zinc, and cobalt and nickel in ore deposits, and silicon and aluminum in igneous rocks. Other associations are, however, equally common. These include sodium and iron, sodium and calcium, and potassium and magnesium in igneous rocks, and lead and silver, lead and zinc, and gold and silver in ore deposits. The latter group of associations are undoubtedly due to processes of differentiation which have resulted in the concentration of these elements in a certain portion of the magma which contained them and there is no reason why the first group should not have become associated as a result of the same causes without any reference to their original relationship. In their chemicaI properties the odd-numbered elements tend to be more like the even-numbered elements that follow them than those which precede them. Among other well known examples of this similarity are vanadium and chromium, manganese and iron, cobalt and nickel, copper and zinc. It is possible that this chemical relationship may indicate a genetic relationship as well. 2
See W. D. Harkins: Phil. Mag., (6) 42,321 (1921). H. S. Washington: Am. J. Sci., 9,376 (1925).
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W. V. HOWARD
The Hypothesis of Atomic Disintegration and the Planetesimal Hypothesis The planetesimal hypothesis may be summarized as follows in so far as it affects the formation of the earth: I . Slow accumulation of planetesimal matter. 2 . Accumulation of atmosphere after the planet had attained a sufficient size to hold it. Additional solid planetesimals were added, however, afterwards so that some of the gases became occluded in the rocks and have been coming to the surface since the beginning of geologic time. 3 . Self compression due to gravity gave rise to sufficient internal heat to cause liquefaction of rocks a t certain places thus promoting volcanic activity. 4. Water vapor in the atmosphere condensed and formed the hydrosphere to which, like the atmosphere, large additions have been made by vulcanism. The chief objection to this theory in the writer’s opinion lies in the idea of an initial volcanic stage caused by compression. If compression gave rise to the initial vulcanism, then a different cause must be assigned to later vulcanism. The authors of the Planetesimal hypothesis tacitly assume that pre-Cambrian vulcanism, especially Archean vulcanism, was more intense than more recent) vulcanism and that therefore pre-Archean vulcanism was probably still more intense. Is it not more reasonable to assume that, except for minor variations, vulcanism is fairly uniform but that Archean vulcanism seems more widespread because of the greater duration of the Archean than, say, the Cenozoic, and also the fact that much of the sedimentary record of the Archean is lost? Barrell’s hot-earth theory is even more difficult to understand. The idea of a globe so heated by great masses of planetesimal matter which come charging into i t becomes almost untenable in the light of the evidence which is accumulating to the effect that the earth is composed of more or less uniform shells which grade into one another. These shells could not have formed unless there was a slow accumulation of matter in a relatively fine state which was added to the central core in inverse order of its specific gravity. Accumulation was probably slow. In fact, considering the small size of the particles, i t is quite possible that all heat of impact and heat of compression was dissipated before the earth had reached its present size. At this point, the theory of radioactive control of mountain-building becomes involved.’ According to this theory vulcanism and mountainbuilding are caused by evolution of heat due to the disintegration of the uranium and thorium series. The chief difficulty in this hypothesis lies in the quantities involved. For example Holmes2 in 1915 shows that with a cooling earth the fact that there is a gradually diminishing amount of radioactive material with depth helps the theory since volcanic temperatures can be more satisfactorily obtained by an earth cooling down from 1000’ with its rate of cooling retarded by radioactivity than by heating by radioactivity alone. 1
J. Joly: “Surface History of the Earth” ( 1 9 2 5 )and earlier papers by Holmes, Joly et al. A. Holmes: “Radioactivity and the Earth’s Thermal History”, Geol. Mag., 52, I I Z
(19x5).
EVOLCTION OF THE ODDNUMBERED ELEMEXTS
I739
Later Holmes’ decided that “there must be more uranium and thorium in the deep-seated rocks than has hitherto been thought possible” because of the necessity of abandoning the theory of a cooling earth. T. C. Chamberlin2 pointed out, as early as 1906 what seems to be the fundamental objection to the radioactive control theory, namely that since radioactivity generates heat sufficient to raise the temperature of rocks to the melting point, the rocks immediately surrounding the radioactive materials must melt and the radioactive materials must therefore be transferred to the surface. The quantity of radioactive material in the earth’s crust must diminish with depth. Anticipating later arguments, it may be pointed out that the ormation of the odd-numbered elements from the even must be accompanied by the evolution of heat. Paraphrasing Chamberlin’s argument, the material in the immediate vicinity of this reaction melts and the odd-numbered elements are transferred to the surface. They are continually being transferred to the surface and since the process of atomic disintegration may be considered as being continuous, there seems to be no reason for assuming the existence of any initial volcanic stage which differed radically in intensity from any later volcanic stage. Introducing this idea into the statement of the planetesimal hypothesis as outlined above, we have:Slow accumulation of planetesimal matter. Disintegration of even-numbered elements to form odd-numbered elements and hydrogen. The hydrogen combined with oxygen to form water which, together with other gases and the melted rocks, rose towards the surface causing volcanic activity. 3 . The water and other gases brought to the surface as a result of vulcanism gave rise to the hydrosphere and atmosphere. Since the hypothesis of atomic disintegration outlined in the foregoing pages has been called on in order to present this modified form of the planetesimal hypothesis, it is necessary to consider several additional points. Is the quantity of heat liberated sufficiently great to account for the following, ( I ) the rise in temperature from a cool globe to one with a thermal gradient such as that of the earth a t present, ( 2 ) the latent heat of fusion of the igneous rocks of the earth’s crust, ( 3 ) the quantity of heat radiated from the earth since the beginning of geological time, (4) the heat absorbed during the process of formation of the complex elements? Would the reaction be periodic so that recurrent periods of mountain building and volcanic activity could take place followed by periods of comparative quiet? What effect would differentiation have on magmas formed according to this hypothesis? I.
2.
‘ A . Holmes: Geol. hIag.,62, 5x4 (1925). “Origin of the Earth” (1906).
2
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W. V. HOWARD
Heat involved in Disintegration I n considering the quantity of heat involved in the process of atomic disintegration, there are several sources of heat as well as several reactions which would tend to absorb heat. Of these, the most important are the disintegration of the even-numbered elements to form odd-numbered elements and atomic hydrogen, the heat of formation of molecular hydrogen, the heat of formation of water, the heat of formation of the elements of higher atomic weight than nickel, and the heat of formation of helium from hydrogen. In calculating the amount of heat generated or absorbed by the disintegration of the even-numbered elements i t is necessary to ascertain whether or not there has been a loss in mass or a gain in mass during the disintegration. Since most of the elements have one or more isotopes, it is difficult to determine whether or not there has been any loss in mass. In fact the only evennumbered. element that is believed to be a simple element which is preceded by an odd-numbered element having the normal relationships to it, is chromium. Here the reaction is as follows:Cr + V H or 52.01 + 50.96 1.0078 51.97 involving a loss in mass of 0.04 g. per gram of hydrogen formed. If, on the other hand, Aston’s latest determinations of mass numbers1 are correct, there would be a gain in mass if odd-numbered elements and H hydrogen are derived from even-numbered elements. Thus if A + C1 35.976 + 34.983 1.00778 35.9908 or a gain in mass of 0.014g. per gram of hydrogen formed. Rutherford states that the energy liberated in the formation of Ig.He from H would be 1.6 X ~ o l caL2 l so that if 4 grams of helium were formed 6.4 X 1ol1 cal. would be liberated and there would be a loss in mass of 0.03I I g. if the atomic weight of helium is 4.00 or if Aston’s determination of the atomic weight is correct, a loss of 0.02896 g. That is, either 2 X I O l3 or 2 . 2 X 1013 cal. are liberated for every gram loss in mass. There are therefore two possibilities. In the first case, there is a loss of mass of between 0.03 and 0.04g. for every gram of hydrogen produced which would amount to 0.9 X 1oZ3g. or 1.2 x 1oZ3g. for the hydrogen present on the earth and this would cause the liberation of between 1.8 and 2.4 X 1 0 calories. I n the second case, heat would be absorbed since the reaction is accompanied by a gain in mass. Here the quantity of heat absorbed would be of the order of iosEcal. Beside this amount of heat the heat liberated by the formation of molecular hydrogen and water (approximately 1 0 3 0 calories) and the amount of heat required for geological processess (also about 1030 calories) is negligible.
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1Proc. Roy. Soc., 115, 487-515 (1927). Nature, 108, 584.
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EVOLUTION OF THE ODD-NUMBERED ELEMESTS
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The amount of helium required for the formation of the elements of higher atomic weight than that of nickel is about 4.8 X 1oZ5grams and since the formation of one gram of helium from radium causes the emission of 226/4 x 3.7 X 109 cal., i t may be assumed that the formation of these more complex elements would absorb 226/4 X 3.7 X iog X 4.8 X 1oZ5 cal. or I x 10~’ calories. The formation of 4.8 x 1026 grams of helium from hydrogen would evolve 4.8 X 1 0 X~ 1.6 ~ X ICPcal. or about 7.7 X 1 0cal. ~ ~ Summing up we have the following possibilities Case I Case I1 - 1 0cal~ z X 1 0cal ~ ~ Disintegration of even-numbered elements - 10% - 10~’ Formation of elements of high atomic weight Formation of helium required for these elements from hydrogen 8 X 1 0 ~ ~8 X 1 0 ~ Formation of molecular hydrogen and water I030 1030 Energy absorbed by geologic processes and radiated into space. - 1030 Obviously there is no way of making these quantities of heat balance at present.
The Formation of Magmas Although this hypothesis is not, in its present state, ready for application to geological theory, there is no doubt but that i t could easily be applied. One of the geologic processes for which no good explanation has been advanced is the formation of magmas which contain juvenile water. According t o the hypothesis of radioactive disintegration within the crust, it is possible to explain the formation of a magma by the heat of disintegration only if we assume an increase in radioactive material at depth. This, as has already been pointed out, seems to be an assumption without much foundation and does not explain satisfactorily the presence of water in the magma. According to the present hypothesis, there is no scarcity of material undergoing disintegration since it includes the even-numbered elements of low atomic weight which make up over 85y0 of the earth’s crust and increase towards the central core of which they make up approximately 99376. Owing to the fact that the material undergoing disintegration occurs in the form of oxides, since very few intrusions contain native metals, and since the odd-numbered elements formed have a lower valence than do the even-numbered elements from which they are derived, oxygen is made available as what might be called a by-product of the disintegration and this oxygen can combine with the hydrogen liberated to form water. The presence of the water reduces the melting point of the rocks with which it is associated and there is a great excess of heat in the neighborhood of the disintegrating elements in any case, so fusion is easily explained. The writer does not believe, ho-xever, that the batholiths and other results of the formation and rise of molten rocks come directly from the area
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W. V. HOWARD
in which the disintegration takes place without being greatly modified by other processes. It is conceivable that masses of almost continental size form the parent magma and that differentiation through gravitative adjustment results in the drawing off of the lighter constituents of this magma and their concentration in smaller reservoirs from which they begin to move towards the surface. Meanwhile, the larger mass beneath solidifies and disintegration begins afresh to result in the formation of another magma a t a later time from which the differentiates may again move upwards following either the path of the earlier intrusions or another path. Katurally the rising magma may be greatly modified by assimilation and there will certainly be further differentiation with the splitting off of subsidary masses. Owing to the fact that nothing can be stated regarding the rate of disintegration, and nothing is known as to the amount of heat evolved, the size of the original masses of magma, or their depth, or the rate of flow of material towards the surface it is useless to speculate regarding the length of time t h a t elapses between the formation of magmas in any one area. It is evident, however, that there will be a certain periodicity to the process and also that the interval between the periods of activity mill be extremely long. Whether or not this interval is the interval between revolutions on the earth’s crust cannot be stated definitely, but it seems reasonable to believe that this is the case. The hypothesis, therefore, falls into the same category as a number of hypotheses at present employed in geological theory. Like the others, it wrtuld explain a great deal if me had sufficient data. Before going farther and developing an imposing structure on such a foundation, the writer presents the foundation alone in the hope that it will be considered from a physical and chemical standpoint in order to find out whether or not it will stand.
Acknowledgments This paper was examined in manuscript by Dr. -4.L. Day and Dr. H. S. Washington of the Geophysical Laboratory, and Professors W. A. Noyes and Jakob Xunz of the Cniversity of Illinois in order that any major errors might be detected. The wrlter wishes to acknoivledge with deep gratitude the assistance afforded by these gentlemen without in any way implying that they consider the hypothesis more than an interesting speculation.
