REVIEW OF THE EVIDENCE
The discrepancy between the geological and radioactive
methods of estimating time—Uniformity of the rate of
decay of uranium—Joly’s criticism—Comparison of the two
time-scales—Doubtful assumptions made in the geological
arguments—Possibility of reconciliation no longer hopeless.
Of the various methods which have been devised to solve the problem of
the earth’s age, only two, the geological and the radioactive, have
successfully withstood the force of destructive criticism. The other
arguments may be dismissed without further discussion, as in every
case their cogency has been vitiated by the detection of a fundamental
error. From the mists of controversy which for half a century have
hung over the subject, the two _hour-glass_ methods alone emerge,
and the final issue must be fought out between them. In the one the
world itself is the hour-glass, and the accumulating materials are
salt, the sedimentary rocks and calcium carbonate. Three concordant
sets of results may be drawn from this triple scheme of measurement,
but it must not be supposed that they are altogether independent. Each
set of data is intimately related to the others and all stand or fall
together. In the other case the accumulating materials are helium and
lead, and the hour-glass is constituted by the minerals in which they
collect. Provided that the field-evidence is clear and convincing
and that the relative geological age of a mineral specimen can be
determined, the construction of an exact and precise time-scale is
a task which can be dealt with successfully in the laboratory. The
problem has advanced from the qualitative to the quantitative stage,
and for the first time in historical geology accurate measurement
founded on delicate experimental work has become possible.
It is a matter for regret that confidence in this pioneer work has
been shaken by the advocates of the geological methods of attack. The
surprises which radioactivity had in store for us have not always been
received as hospitably as they deserved. With the advent of radium
geologists were put under a great obligation, for the old controversy
was settled overwhelmingly in their favour. But the pendulum has swung
too far, and many geologists feel it impossible to accept what they
consider the excessive periods of time which seem to be inferred.
That there exists a serious discrepancy obviously points to a flaw
in the underlying assumptions of one or the other or both of the
methods. Evidently we are at the parting of the ways. The fundamental
assumptions on which the arguments are based cannot both be right.
One of them must be rejected. Which is it to be? Let us consider each
in turn, and discuss the consequences of the two possible forms of
reconciliation.
The only assumption which can reasonably be called into question is
that of uniformity, and it is involved equally in both calculations. It
is here, at the root of the problem, that the discrepancy really lies.
If we favour the uniformity of geological processes—a well-worn
doctrine which has done good service—then we must reject uniformity
of radioactive disintegration. Joly has drawn attention to the latter
possibility. He asks: Is it assured that the parent substance, uranium,
has always in the past disintegrated at the rate determined by its
present average life period? As far as we know, the rate of decay
for substances of rapid transformation is constant, and independent
of temperature and pressure changes. On the grounds that a large
number of radioactive bodies decay at a constant rate, it is believed
that this constancy is a definite attribute of all the radioactive
elements. In the case of uranium this assumption cannot be proved for
periods commensurate with its half-life period. On analogy with the
behaviour of the shorter lived elements, it is probable that had we
lived in Cambrian times and experimented with Archean uranium-bearing
minerals just as has been done during the last decade, the half-life
period would then have been exactly the same as we now find it—about
5400 million years. In the case of radium emanation there can be no
doubt that experiments in Cambrian times would have given results
concordant with ours. It would be as unphilosophic to doubt this as
to believe that the laws of physics and chemistry vary with time. The
difference between uranium and its daughter elements, the difference
which suggests to Joly a possible distinction, is simply one of origin.
We are in complete ignorance of the genesis of uranium. It is not
impossible that, owing its origin to some process other than atomic
transformation, the particular distribution of intrinsic energy among
its atoms may not be such as to maintain a constant rate of decay.
At the moment of its birth every radioactive atom has a definite
expectancy of life, and when a sufficiently large number of atoms is
under observation a definite fraction disintegrates every second. There
is this difference in the case of parent elements. As they become aged
with reference to the time of their origin, they are not reinforced
by the addition of fresh, newly-born atoms, as are the other members
of each series. Joly’s supposition seems to be that in the absence
of this reinforcement the uranium in its early stages may possibly
disintegrate more rapidly than it does now. However, it is not found
that the younger atoms of the short-lived elements are, on an average,
more prone to rapid decay than are their older companions. Whether an
element is in equilibrium with the higher members of its family, or
whether it is separated from them, its transformation proceeds with
unaffected regularity.
It is very improbable that reconciliation will be found in the
supposition of a progressive retardation of the rate of decay of
uranium. There are three possibilities. Uranium may have disintegrated
in the past exactly as it now does; or it may have decayed more slowly
or more rapidly. The latter two alternatives do not favourably commend
themselves. There is no evidence which can be cited in their support.
On the other hand, the hypothesis of _constant_ change is deduced
from a well-established series of experimental facts, and is remarkably
in accordance with the general phenomena of radioactivity. Uranium,
in other respects, does not present any anomaly, and with regard
to the mechanism of its decay physicists are not likely to regard
it as an exceptional case without very definite reasons for doing
so. The discordance between the time estimates drawn from the rates
of geological and radioactive changes cannot be held to constitute
a sufficient reason for rejecting current opinions unless it is
conclusively demonstrated that the geological estimates are beyond
question. In the future the case for uranium may be established
more securely, when the dynamics of atomic disintegration, and the
conditions upon which the distribution of unstable atoms depends,
becomes more intimately understood. At present there is only one
means of testing the constancy of uranium decay, but unfortunately
it affords only negative evidence. The range of α-particles from a
radioactive element is connected in some way with its rate of decay.
If then, uranium in the past disintegrated more rapidly, the radius of
its particular pleochroic halo ought to record the difference. It is
improbable that any variation—assuming for the moment that there were
a variation—could be detected even in the most favourable cases.
We now turn with a double interest to the geological estimates. If it
can be shown that they ought to be largely increased, as Chamberlin
and a few other geologists believe, then not only is a reconciliation
at once made possible, but, in turn, the constancy of uranium decay is
placed beyond doubt. Little need be added to the discussion in Chapter
VI. It was there indicated that one factor previously over-looked—the
average height of the continents in geological time—very largely
controls the rate of denudation and therefore of sedimentation. Let us
make an attempt to discover how past rates must be related to those
of the present to make possible a complete reconciliation. In Fig. 17
the discrepancy is illustrated graphically by comparing the respective
time scales from the close of the Archean (gneiss and granite phase) to
the present day. All the sediments of which relics have remained to us
are in this way taken into consideration. Lying buried in the Archean,
the base of the record is obscured beyond recognition by the prevalence
of metamorphic and plutonic igneous rocks. The extent to which the
earliest sediments have been lost in the evolution of the earth’s
crust, and the part they have played in the genesis of granites and
gneisses are questions which betray our ignorance and offer food merely
for wild speculations. These possibilities, however, do not touch the
immediate point at issue, for in their time relations they lie outside
the limits to which this discussion is restricted.
The curve A is plotted strictly against the maximum observed thickness
of sediments, and corresponding to it is the sedimentation line A′
to which is granted 300 million years. According to these two graphs
the greatest error lies beyond the Cambrian. The average rate of
denudation and of sediment accumulation must now be nine times that
of the pre-Cambrian periods, but if post-Cambrian is compared with
present the ratio is reduced to two-and-a-half. In the B series, the
lead ratios are plotted in a straight line and the stratigraphical
column is extended in accordance with the palæontological evidence that
pre-Cambrian time is at least as long as that which has elapsed since
the beginning of the Cambrian. On this basis present rates are four
times the average for post-Archean time.
[Illustration: FIG. 17.
Geological Time Scales.]
Assuming that the true time-scale lies somewhere between the extremes
of A and B, we are led to two conclusions which, if accepted, greatly
lessen the severity of the discordance between A and A′ and B and
B′. From A and A′ it appears that pre-Cambrian denudation took place
much more slowly than has since been typical. This proposition is in
complete accordance with the view that the pre-Cambrian continents,
when viewed in the light of the reconstructed geographies of the later
periods, were of limited area and restricted elevation. From B and
B′ the broad time conception of palæontology gains further support,
and the existence of great gaps in the pre-Cambrian succession is
suggested. It is well known that the most important unconformities of
the whole geological record are to be found in the imperfect succession
of the earliest formations. It is impossible to do more than guess
at the duration of time periods which are without their sedimentary
equivalents. On the most extreme assumption, the Algonkian sediments
should be represented not by 82,000 feet, but by more than 300,000
feet. Unwilling though we may be to consider the record imperfect to
this incredible degree, it is of importance to point out that had such
an immense thickness existed in successive periods of time, the sodium
content of the ocean would not necessarily be in any way different
from what it is. The same amount of primary rock material may have
been broken up, but instead of a reassorting of the materials to form
three successive sets of sediments (on a rough average) we would be
obliged to postulate six or more repetitions of the sorting process.
The question need not be pursued farther. The suggestion here put
forward is, that in the limitations of pre-Cambrian geography and in
the imperfection of the sedimentary relics of those remote times, the
discrepancy which is peculiar to the pre-Cambrian finds an adequate
explanation.
If this be allowed, all that remains is to decide whether it is
inconsistent with geological principles to assert that the modern
hour-glass is running at two-and-a-half to four times its average
rate. The decision depends largely on the broad point of view from
which geological interpretation proceeds. From the standpoint of
Catastrophism little progress was made. Uniformity proved a great
advance, but in detail it is apt to lead us astray if applied too
dogmatically. Modern interpretation is based on the more philosophic
conception of Evolution, and in place of the earlier idea which was
insisted upon by the older physicists—that changes have been such as
would accompany a gradual running down of the earth’s internal kinetic
energy—the _form_ of development now favoured is that of cycles
of phenomena, recurring in their broad features again and again and not
necessarily hampered in their activity by any progressive diminution in
the store of available energy. Igneous action, deposition of sediments,
marine transgression and recession, are all rhymic phenomena and
the factor common to each one, whether as cause or effect, is
earth-movement.
The conditions of the present day cannot then be accepted as
representing average conditions, unless it were by a happy accident.
Amidst all the details of earthquakes and volcanic eruptions some great
cycle is now running its course, and only in relation to the particular
phase of the cycle under which we happen to pursue our investigations
will our conclusions be strictly tenable. Although we cannot hope to
judge the exact place which the present takes in the larger scheme of
terrestrial activity, yet in comparison with the past, the present
epoch would seem to approach just those extremes most favourable to
a high rate of denudation, and to a rapid accumulation of sediments.
Marine recession, brought about by deepening of the ocean basins, and
raising of the land areas have together brought about continental
expansion and elevation. The vulcanism of the present day, whether
regarded as a closing phase of a period of igneous action, or as the
initiation of a new cycle, probably affords an example of more than
average intensity and violence. The weathering capacity of rain must be
enhanced in proportion to its content of dissolved acid gases, and this
in turn is conditioned by the prevalence of vulcanism. Still another
factor leading to higher rates, though of a different category, is
due to recent glaciation. Over wide areas easily eroded deposits are
exposed, the areas being generally those which would resist denudation
most successfully. In Fennoscandia, for example, four-fifths of the
pre-Cambrian shield is buried beneath a thin covering of moraine.
It is not suggested that present rates have never before been reached,
but only that they are characteristic of the more intense phases of
denudation rather than of average conditions. If this be granted,
reconciliation of the rival time estimates is no longer hopeless. There
can be no doubt that agreement will never be brought about by the more
convincing testimony of experimental demonstration. It must be almost
entirely a question of interpretation. An attempt has been made to show
that in the geological evidence there is nothing impossibly at variance
with the dictates of the radioactive minerals. With the acceptance of
a reliable time-scale, geology will have gained an invaluable key to
further discovery. In every branch of the science its mission will be
to unify and correlate, and with its help a fresh light will be thrown
on the more fascinating problems of the Earth and its Past.
APPENDIX A
(_a_) _Kinetic Energy of α-particles_
1 gram of radium in equilibrium with emanation,
Ra. A B and C generates heat at the rate of =132
calories per hour= (85% due to α-particles).
e = charge on α-particle = 9·3 × 10⁻¹⁰ E.S. units.
= 3·1 x 10⁻²⁰ E.M. ”
m = mass of α-particle }
v = velocity of α-particle } see Table below.
N = number of α-particles liberated from 1 gram of
radium = 3·4 × 10¹⁰ per second.
Energy E transformed per second is given by—
Nmv²
E = ½∑ ——— × e
e
Ne mv²
= —— ∑ ——
2 e
+---------------+---------------+----------------+
| | v | mv²/e |
| Element. | Cms. per sec. | E.M. Units. |
+---------------+---------------+----------------+
| Radium | 1·56 × 10⁹ | 4·78 × 10¹⁴ |
| Ra. emanation | 1·70 × 10⁹ | 5·65 × 10¹⁴ |
| Ra. A | 1·77 × 10⁹ | 6·12 × 10¹⁴ |
| Ra. C | 2·06 × 10⁹ | 8·37 × 10¹⁴ |
+---------------+---------------+----------------+
Substituting these values, we have—
Ne = 3·4 × 10¹⁰ × 3·1 × 10⁻²⁰ = 10·5 × 10⁻¹⁰ E.M. units.
mv²
∑ —— = 10¹⁴(4·78 + 5·65 + 6·12 + 8·37)
e
= 24·9 × 10¹⁴ E.M. units;
whence E = 13·1 × 10⁵ ergs per second
= 4·73 × 10⁹ ergs per hour.
Now 4·19 × 10⁷ ergs = 1 gram-calorie.
∴ E = 113 calories per hour.
(_b_) _Production of helium from Uranium and Thorium in
equilibrium with all their disintegration products._
_Uranium_—
N = number of helium atoms liberated from 1 gram
of radium alone = 3·4 × 10¹⁰ per second.
(_Rutherford and Geiger_, 1908).
The equilibrium ratio of radium to uranium is
3·4 × 10⁻⁷. Hence for each gram of uranium in
equilibrium the number of atoms produced amounts to—
3·4 × 10¹⁰ × 3·4 × 10⁻⁷ × 8 per second = 29·1 × 10¹¹ per year.
Now the number of helium molecules, and therefore of atoms,
in 1 cc. of the gas at N.P.T. is 2·72 × 10¹⁹.
The annual production of helium must consequently be
29·1 × 10¹¹
———————————— ccs.,
2·72 × 10¹⁹
i.e. 10·7 × 10⁻⁸ ccs., or 1·88 × 10⁻¹¹ grs. per gram of uranium.
An experimental determination gave 10·6 × 10⁻⁸ ccs.
(_Strutt_, 1910).
_Thorium_—
The ionising power, or the energy of the α-particles from 1 gram of
thorium, is 0·325 of that from 1 gram of uranium, each element being in
complete equilibrium.
Average range of α-particles from thorium and its products = 5·4 cms.
Average range of α-particles from uranium and its products = 4·3 cms.
The average thorium α-particle is therefore 1·25 times as energetic as
the average uranium α-particle.
Hence the actual production of α-particles or helium atoms from
thorium is only 0·325/1·25 = 0·26 of that of uranium.
Experimental determinations 0·23 (_Strutt_, 1910),
0·27 (_Rutherford and Geiger_, 1910).
(_c_) _Half-life Period of Radium._
(1) The number of α-particles emitted from 1 gram of radium per second
(n = 3·4 × 10¹⁰) is equal to the number of atoms disintegrating per
second.
If N is the number of atoms in 1 gr. radium, then λ, the fraction which
transforms per second, is given by—
n
λ = ——.
N
The number of atoms in 1 gr. hydrogen is 6·24 × 10²³,
and as the atomic weight of radium is 226 times that
of hydrogen,
N = 2·76 × 10²¹.
∴ λ = 1·25 × 10⁻¹¹ gr. per sec.
= 3·94 × 10⁻⁴ gr. per year.
=Half-Life period= = 0·69315/λ = =1760 years=.
(2) 1 gr. of radium is in radioactive equilibrium with 0·58 cubic
millimetre, or 5·7 × 10⁻⁶ grs. of emanation (atomic wt. = 222).
If λ₁ = 2·085 × 10⁻⁶ is the fraction of emanation transforming per
second, we have—
λ = 5·7 × 10⁻⁶ × λ₁
= 1·19 × 10¹¹ gr. per sec.;
whence—=Half-Life period = 1850 years.=
The earlier values given for the half-life period were 1760 and 2000
years, but the lower figure seems most accurate, with 1850 years as a
probable value.
The half-life of uranium would then be—
1850
—————————— = =5400 million years=.
3·4 × 10⁻⁷
(_d_) _Time-Average of Uranium_
Uₜ = Quantity of uranium remaining after a time t.
Uₒ = Quantity of uranium originally present (t = o).
Uₘ = Time-average of uranium during time t.
λ = Disintegration constant of uranium.
Pbₜ = Lead accumulated during time t.
Heₜ = Helium ” ” time t.
[Illustration: Graph I]
Graph I represents the rate of decay of uranium—according to the
exponential law—
( -λₜ)
Uₜ = Uₒ ( e ).
There is one rate of decay which, if it remained constant throughout
the time t, would have a total effect equivalent to that produced by
the actual slowly decreasing rate of decay. This average rate is
represented by some point on the curve, and the corresponding quantity
of uranium, Uₘ, is the time-average. Equating the amount of uranium
transformed in each case, we have—
Uₒ - Uₗ = λUₘt
Uₒ - Uₜ
whence Uₘ = ———————— (_a_).
λt
[Illustration: Graph II]
For periods less than 2000 million years, the time-average is nearly
equal to the arithmetic mean of Uₒ and Uₗ.
Uₒ + Uₗ
Uₘ = ———————— (_b_).
2
The value of Uₘ for 2000 million years is,
according to equation (_a_), equal to 0·874 Uₒ
and ” ” ” (_b_) ” “ 0·879 Uₒ.
The ages of minerals rarely exceed 1500 million years, and therefore
the error involved by using equation (_a_) in preference to
(_b_) is quite negligible.
In Graph II the ratio Uₘ/Uₜ, i.e. the factor by which the present
uranium content of a mineral must be multiplied in order to obtain the
true time-average, is plotted against time.
An approximation to the age, t, of a mineral is afforded by the ratio
Pbₜ/Uₜ. From the graph the factor corresponding to this time can be
obtained, and thence the time-average. This in turn can be utilised to
give the more correct age represented by Pbₜ/Uₘ.
A more straightforward method of correction is as follows:
Uₒ can be determined from known quantities according to the following
equation:
Uₔ = Uₜ + Pbₜ + Heₜ
= Uₜ + 1·15 Pbₜ;
whence, =Uₘ = Uₗ + 0·575 Pbₜ=.
The age of the mineral is then given by the ratio =Pbₜ/Uₘ=, or
directly from Graph II.
(_e_) _Analyses made by the Author of Radium in Igneous Rocks_
(_cited on p. 130_)
_Acid Rocks_— _Ra. per gram of rock_
Granite, Mozambique 5·84 × 10⁻¹² grs.
” ” 2·61 ”
” ” 1·77 ”
” N. Nigeria 3·09 ”
” Rhodesia 2·43 ”
” Transvaal 2·12 ”
” South Africa 1·81 ”
” ” ” 2·73 ”
_Basic Rocks_—
Basalt, Mozambique 0·94 × 10⁻¹² grs.
Dolerite ” 0·85 ”
Gabbro ” 1·07 ”
Norite ” 0·54 ”
_Ultrabasic Rocks_—
Composite analysis of 10 specimens from
Scotland, New Zealand, Africa,
and Canada 0·51 × 10⁻¹² grs.
APPENDIX B
BIBLIOGRAPHY
CHAPTER I
Thomson (Kelvin). _Rep. Brit. Ass._, p. 1819. 1855.
—— _Proc. Glasgow Phil. Soc._, Vol. IV, p. 272. 1860.
—— _Phil. Mag._, February, 1862, p. 158. 1861.
—— _Popular Lectures and Addresses_
[_P.L.A._], Vol. I, p. 349. 1862.
—— _Natural Philosophy_, Appendix D.
—— _P.L.A._, Vol. II, p. 6. 1865.
—— _P.L.A._, Vol. II, p. 10. 1868.
Huxley. _Presidential Address, Quart. Journ. Geol. Soc. 1869._
Thomson. _P.L.A._, Vol. II, p. 73. 1869.
—— _P.L.A._, Vol. II, p. 238. 1876.
—— _P.L.A._, Vol. I, p. 369. 1887.
King. _Am. Journ. Science_, p. 1. 1893.
Correspondence in _Nature_. Perry, Kelvin, Tait.
January 3rd, March 7th, April 18th. 1895.
Poulton. _Rep. Brit. Ass._, p. 808. 1896.
Kelvin. _Phil. Mag._, January, 1899, p. 66. 1897.
Correspondence in _Nature_. 1903.
Wilson. July 9th.
Darwin. September 24th.
Joly. October 1st.
Correspondence in _Nature_.
Kelvin, Strutt, Lodge, etc. September 20th. 1906.
For other references see below.
CHAPTER II
Chamberlin and Salisbury. _Geology_, Vol. II, Chaps. I and II. 1909.
T. C. Chamberlin and other Writers. _The Tidal Problem._
Carnegie Inst. of Washington. Pub. No. 107. 1909.
Darwin. _The Tides._ 1911.
Poincaré. _Hypothèses cosmogoniques._ Paris. 1911.
CHAPTER III
Croll. _Phil. Mag._ May, 1868.
—— _Climate and Time._ 1875.
De Geer. _Geol. Fören i Stockholm Föhr Band 32._ 1910.
Gilbert. _Journ. of Geol._, Vol. III, p. 121. 1895.
Lowell. _Evolution of Worlds_, p. 197. 1910.
Sederholm. _Bull. Comm. Géol. de Finlande_, No. 30, pp. 7-15. 1911.
Sollas. _Ancient Hunters._ 1911.
CHAPTER IV
Babb. _Science_, Vol. XXI, p. 343. 1893.
Clarke. _Data of Geo. Chemistry. Geol. Sur., U.S.A. Bull. 491._
—— _Smith. Misc. Collect._, Vol. LVI, No. 5. 1910.
Dittmar. _Challenger_ Report, Vol. I, p. 203. 1884.
Dole and Stabler. _Water Supply Papers. Geol. Sur., U.S.A._,
Nos. 234 and 236. 1910.
Geikie. _Trans. Geol. Soc., Glasgow_, p. 153. 1868.
Humphreys and Abbott. _Physics and Hydraulics of Mississippi River_,
p. 148. 1876.
Merrill. _Rocks, Rock weathering and Soils._ 1897.
Murray. _Scot. Geog. Mag._, Vol. III, p. 65. 1887.
—— _Scot. Geog. Mag._, Vol. IV, p. 38. 1888.
Reade. _Chemical Denudation in Relation to Geological Time._ 1901.
Russell. _River Development._ 1898.
Schwarz. _Causal Geology._ 1910.
Tylor. _Phil. Mag._, April, p. 258. 1853.
CHAPTER V
Ackroyd. _Chem. News_, p. 265. 1901.
—— _Geol. Mag._, p. 445 and p. 558. 1901.
Becker. _Science_, Vol. XXXI, p. 459. 1910.
—— _Smith. Misc. Collect._, Vol. LVI, No. 6. 1910.
Clarke. _Smith. Misc. Collect._, Vol. LVI, No. 5. 1910.
—— _Proc. Am. Phil. Soc._, p. 214. 1912.
Fisher. _Geol. Mag._, p. 124 and p. 132. 1900.
Halley. _Phil. Trans._, Vol XXIX, p. 296. 1715.
Hanamann. _Landesdurchforschung Böhmens. Archiv.
Natur._, Vol. IX. Vol. X. 1894. 1898.
—— _Cited in Clarke’s Data_, 2nd ed., p. 92.
Joly. _Trans. Roy. Soc., Dublin_, Vol. VII, p. 23. 1899.
—— _Rep. Brit. Ass._, p. 369. 1900.
—— _Geol. Mag._, p. 344 and p. 504. 1901.
—— _Radioactivity and Geology_, p. 236. 1909.
—— _Phil. Mag._, p. 357. September, 1911.
Karsten. _Inaug. Diss., Kiel._ 1894.
Rudzki. _Bull. Acad. Sci., Cracovie._ February, 1901.
Sollas. _Presidential Address, Quar. Journ. Geol. Soc._,
Vol. LXV. 1909.
CHAPTER VI
Blake. _Geol. Mag._, p. 72. 1903.
Croll. _Stellar Evolution_, p. 48. 1889.
Geikie. _Rep. Brit. Ass._ 1892.
—— _Nature._ August 4th, 1892.
—— _Rep. Brit. Ass._, p. 727. 1899.
Haughton. _Manual of Geology_, p. 101. 1871.
—— _Nature_, p. 266. 1878.
Holmes. _Nature._ July 6th, 1911.
Joly. _Radioactivity and Geology._ 1909.
de Lapparent. _Bull. Soc. Géol. de France_,
Vol. XVIII, p. 351. 1890.
—— _Géologie_, p. 225, p. 261, and p. 1958. 1906.
Lyell. _Principles._ Tenth Edn., Vol. I, p. 301. 1867.
McGee. _Science_, Vol. XXI, p. 309. 1893.
Phillips. _Life on the Earth_, p. 119. 1860.
Reade. _Geol. Mag._, p. 99. 1893.
Sederholm. _Naturen, Helsingfors_, Nos. 33 and 34. 1897.
Sollas. _Nature._ April 4th, 1895.
—— _Rep. Brit. Ass._, p. 711. 1900.
—— _The Age of the Earth and other Geological Studies._ 1905.
—— _Presidential Address, Quar. Journ. Geol. Soc._,
Vol. LXV. 1909.
Upham. _Am. Journ. Science_, Vol. XLV, p. 217. 1893.
Walcott. _Journ. Geol._, Vol. I, p. 675. 1893.
Watts. _Presidential Address, Quar. Journ. Geol. Soc._,
Vol. LXVII. 1911.
Wallace. _Island Life_, p. 222. 1892.
Winchell. _World Life_, Chicago, p. 378. 1883.
CHAPTER VII
Mme. Curie. _Traité de Radioactivité._ 1910.
Ramsay and Soddy. _Proc. Roy. Soc. A._, Vol. LXXII, p. 204. 1903.
Russell. _Proc. Roy. Soc. A._, Vol. LXXXVI, p. 240. 1912.
Rutherford. _Radioactive Substances._ 1912.
Rutherford and Soddy. _Phil. Mag._, Vol. IV, p. 582. 1902.
Rutherford and Geiger. _Proc. Roy. Soc. A._,
Vol. LXXXI, p. 151. 1908.
Rutherford and Royds. _Phil. Mag._, Vol. XVII, p. 281. 1909.
Whytlaw-Gray and Ramsay. _Proc. Roy. Soc. A._,
Vol. LXXXVI, p. 270. 1912.
CHAPTER VIII
Abbott. _The Sun._ 1910.
Arrhenius. _The Life of the Universe_, Vol. II, p. 193.
Helmholtz. _Phil. Mag._, p. 516. 1856.
Rutherford and Soddy. _Phil. Mag._ May, 1903.
CHAPTER IX
Becker. _Bull. Geol. Soc. Am._, p. 113. 1908.
—— _Smith. Inst. Misc. Collect._, Vol. LVI, No. 6.
Buchner. _Proc. Konink. Akad. van Wetensch. te Amsterdam._
October, 1910, February, 1911, and April, 1912.
Chamberlin. _Journ. Geol._, p. 674. 1911.
Eve and McIntosh. _Phil. Mag._ August, 1907.
—— _Trans. Roy. Soc. Canada_, p. 69. 1910.
Farr and Florance. _Phil. Mag._ November, 1909.
Fletcher. _Phil. Mag._ July, 1910.
—— _Phil. Mag._ January, 1911.
—— _Phil. Mag._ June, 1911.
—— _Phil. Mag._ February. 1912.
Joly. _Rep. Brit. Ass._, p. 677. 1908.
—— _Radioactivity and Geology_, 1909.
—— _Phil. Mag._ October, 1909.
—— _Phil. Mag._ July and August, 1910.
—— _Phil. Mag._ July, 1911.
—— _Cong. Internat. de Rad. and d’Elec._, p. 370. 1911.
—— _Phil. Mag._ February, 1912.
—— _Phil. Mag._ October, 1912.
King. _Am. Journ. Science_, p. 1. 1893.
Strutt. _Proc. Roy. Soc. A._, Vol. LXXIX, p. 472. 1906.
—— _Proc. Roy. Soc. A._, Vol. LXXXIV, p. 377. 1910.
Suzuki. _Proc. Math.-Phys. Soc., Tokyo_, p. 204. 1912.
CHAPTER X
Becker. _Bull. Geol. Soc., Am._, Vol. XIX, p. 113. 1908.
Boltwood. _Am. Journ. Science_, p. 260. 1905.
—— _Am. Journ. Science_, Vol. XXIII, p. 77. 1907.
Boltwood and Rutherford. _Phil. Mag._, Vol. XXII, p. 586. 1911.
Dewar. _Proc. Roy. Soc. A._, Vol. LXXXI, p. 280. 1908.
—— _Proc. Roy. Soc. A._, Vol. LXXXIII, p. 404, 1910.
Holmes. _Proc. Roy. Soc. A._, Vol. LXXXV, p. 248, 1911.
Joly. _Radioactivity and Geology_, p. 211. 1909.
—— _Phil. Mag._ September, 1911.
Kœnigsberger. _Geol. Rundschau_, Vol. I, p. 245. 1910.
Rutherford. _Radioactivity_, p. 486. 1905.
Strutt. _The Accumulation of Helium._
—— _Proc. Roy. Soc. A._, Vol. LXXXI, p. 272. 1908.
—— —— Vol. LXXXII, p. 166. 1909.
—— —— Vol. LXXXIII, p. 96. 1910.
—— —— Vol. LXXXIII, p. 298. 1910.
—— —— Vol. LXXXIV, p. 195. 1910.
—— —— Vol. LXXXIV, p. 380. 1910.
[Illustration: THE RADIOACTIVE ELEMENTS
URANIUM FAMILY
ACTINIUM FAMILY
THORIUM FAMILY]
INDEX
α-particles, deflection of, 94
— nature of, 95
— penetration of, 94, 107, 108
— heating effect of, 96, 97
— kinetic energy of, 177
— atoms of helium, 96
Actinium and uranium, 100
Adams, 25
Age of earth, 86, 89, 125, 157
— minerals, 154-64
— moon, 15, 27
— oceans, 68, 89
— sediments, 86, 89
— sun, 112, 113, 120
Arrhenius, energy of sun, 117
Atmosphere, origin of, 25, 30
— as thermal blanket, 36
Atomic theory, 40
Atoms in 1 cc. helium, 140
— in 1 gr. hydrogen, 179
— in 1 gr. radium, 179
— disintegration of, 98, 102
— constitution of, 102
Autunite, age of, 100, 153
— radium-ratio in, 100
— lead-ratio in, 153
β-particles, deflection of, 94
— nature of, 95
— from potassium, 103
Barus, diabase fusion point, 125, 126
Barnes and Rutherford, heat output of radium, 101
Basic rocks, radium in, 130
— distribution of, 128, 134
Becker, age of oceans, 62, 63, 70
— age of earth, 127
Becquerel, discovery of radioactivity, 92
Becquerel rays, 93
Biology and the earth’s age, 20, 21
Boltwood,constancy of radium-ratio, 99
— origin of actinium, 100
— test of lead-ratio, 158
Boltwood and Rutherford, production of helium, 139
Bragg, ionisation, 107
Bückner, radium in rocks, 130
Buffon, 23
Calcium carbonate, accumulation of, 88, 89
Catastrophism, 4, 8
Chaldean chronology, 2
Chamberlin, planetismal hypothesis, 28-30
— tidal theory, 27
— rate of denudation, 79, 80, 81
_Challenger_ expedition, 85
Chlorine in rain, 66
— in rivers, 53, 70
— in sea, 53
— in rocks, 70
Chronology, Chaldean, 2
— Persian, 3
— Hebrew, 3
— Indian, 3
— Byzantine, 4
Clarke, sodium in rocks, 67, 70, 71
— chemical denudation, 51-3
— volume of oceans, 63
— age of oceans, 63, 66
Cosmical energy, 120
Croll, glacial theory, 35-9
— marine erosion, 58
— age of earth, 86
Crust of earth, thickness of, 128, 134
— evolution of, 30, 134
Crystallisation of rock magmas, 145-8
Curie, Mme., radioactivity of thorium, 92
— discovery of radium, 93
Curie and Laborde, heating effect of radium, 96, 101
Cuvier, 8
Cycles of denudation and deposition, 85, 174, 175
Cyclic sedimentation, 44
— circulation of salt, 66-70
Dana, volume of limestone, 88
Darwin, geological time, 11
Darwin, Sir G., moon’s history, 15, 19
— age of moon, 27
Decay, radioactive, 98
— physical independence of, 102
— possible variation with time, 168
Deep-sea deposits, 59
Deluge, 4, 8
Denudation, initiation of, 25, 31
Denudation, chemical, 50, 54
— mechanical, 54
— marine, 58, 66
— present rates of, 78, 80
Deposition, 47, 81-5
Dewar, production of helium, 140
Diabase, fusion point, 125, 126, 128
Dittmar, salinity of oceans, 64
Dole and Stabler, denudation of N. America, 50, 55
Duane, heating effect of radium, 101
Earth, origin of, 22 _et seq._
— early history of, 25, 29, 73
— heat of, 12-16, 30, 122
— interior of, 134
— distribution of radium, 131-5
Earthquakes, 134
Electroscope, 93, 104
Emanation of radium, 97, 104
End products, 100, 140
Energy, conservation of, 11, 111
Eve and McIntosh, radium in rocks, 130
Farr and Florance, radium in rocks, 130
Fletcher, radium in rocks, 130
Fossils, early ideas, 5
γ-rays, nature of, 94
Geer, De, glacial clays, 41-4
Geiger and Rutherford, counting of α-particles, 138
Geikie, age of earth, 86
— marine erosion, 58
— on geological time, 78
Glacial periods, 33
Glacial periods, chronology of, 36 _et seq._
Glacial clays in Sweden, 41
Glaciation, indications of, 33, 34
— cause of, 35
Gilbert, Cretaceous sediments of Colorado, 44
Haloes, pleochroic, 107-9
Halley, salinity of oceans, 61
Heat, emission of, by radium, 96, 97, 101
— — by uranium, 116, 131, 132
— — by thorium, 116, 132
— escaping from earth, 122-4, 132
— of the sun, 110 _et seq._
Helium, discovery of, 95, 96
— from radio-elements, 96
— rate of evolution of, 138
— leakage of, 149
— as end product, 149
— accumulation of, 154
— — in phosphates, 154
— — in iron ores, 155
— — in zircons, 156
— — in sphenes, 156
Helium-ratio, as age-index, 143
Helmholtz, 12, 112
Hutton, 7, 22
Huxley, reply to Kelvin, 14, 20
Igneous rocks, exposures of, 71, 72, 73
— sodium in, 67
— radium in, 131
— thorium in, 131
Ionisation, 93, 104
Ionium, 99
Iron meteorites, 134
Iron ores, helium in, 155
Joly, estimation of radium, 105
— — thorium, 107
— radium in rocks, 131
— thorium in rocks, 131
— age of the earth, 86
— age of the oceans, 17, 20, 62
— on radioactive decay, 168
Kant, 23, 26, 110
Kelvin, duration of earth’s heat, 12-17, 124, 125
— — sun’s heat, 12-14, 111
— tidal retardation, 13, 26, 27
Lamarck, 8
Land, area of, 52
— degradation of, 57
Laplace, 23, 28, 35
Laplacian hypothesis, 23-25
— difficulties of, 28
Lapparent, de, 86
Lead in igneous rocks, 147
— genetic connection with uranium, 100, 140, 141
— in uranium minerals, 158-164
— rate of production of, 142
Lead-ratio as age-index, 143
Lowell, Polar caps of Mars, 39
Lyell, _Principles_, 9
Mars, Polar caps of, 39
Mass of electron, 95
— of hydrogen atom, 179
Mayer, sun’s heat, 12, 111
Meteorites and sun’s heat, 111
— radium in, 134
Mica, pleochroic haloes in, 109
Minerals, radium-ratio in, 99, 100
— actinium-ratio in, 100
— lead-ratio in, 141, 143
— helium-ratio in, 143
— choice of, 153
Mississippi as denuding agent, 55
— bottom load of, 54
Moon, 15, 19, 20, 27, 28
Moses and geology, 3, 9
Moulton, 28
Murray, area of land, 52
— salinity of rivers, 50
— volume of ocean, 63
Nebulæ, Laplacian, 24, 28
— spiral, 28, 29
Nebular hypothesis, 23-25, 28
Nile, annual deposit of, 81
North America, denudation of, 50, 56
Oceans, origin of, 25, 50
— mass of, 53, 64
— volume of, 53, 63
— saline content of, 53
— age of, 68, 89
Origin of earth, 22, _et seq._
Perry, 16
Phillips, 10
Phosphates, helium in, 154
Phosphorescence of uranium salts, 92
Pitchblende. _See_ Uraninite
Pleochroic haloes, 107-109, 170
Polonium, discovery of, 93
Poulton, biology and geological time, 21
Products, final radioactive, 100, 140
Radioactive disintegration, 98
— — physical independence of, 102
Radioactive layer, 133
Radiation from uranium, 92
Radium, discovery of, 93
— detection of, 93, 103-107
— emanation from, 98, 104
— helium from, 96, 138-140
— α-rays from, 96, 138
— half-life of, 98, 99, 179
— atomic weight of, 142
— genesis from uranium, 99
— heating effect of, 96, 101, 129, 131
— end products of, 100
— in earth’s crust, 103, 131
— in igneous rocks, 131
— in sediments, 131
— in sun, 117
Ramsay, helium in minerals, 96
Reade, chemical denudation, 50, 62
— age of earth, 86
— volume of limestone, 88
River water, volume of, 53
— sediment in, 56, 57
— salinity of, 53
Rocks, radium in, 130, 131
— thorium in, 131
— chlorine in, 70
— sodium in, 67
Röntgen rays, discovery of, 92
— nature of, 94
Runge and Precht, heat output of radium, 101
Rutherford, age of minerals, 154
— Becquerel rays, 93
Rutherford and Barnes, heat output of radium, 101
Rutherford and Geiger, counting of α-particles, 138
Rutherford and Soddy, disintegration hypothesis, 96, 98
— radium and sun’s heat, 116
Schwarz, 49
Schuchert, 78
Schweidler v. and Hess, heat output of radium, 101
Sederholm, annual deposits, 43
— thickness of sediments, 43, 85
Sediment carried by rivers, 57
Sediments, volume of, 65, 68, 88
— pore space of, 65
— thickness of, 43, 44, 76, 77
— rate of deposit of, 81, 84
— rate of accumulation of, 47
— radium in, 131
— thorium in, 131
— sodium in, 67
— on Continental shelf, 83
— oceanic, 59
— time represented by, 86
Sedimentation, cyclic, 41, 43, 44
Soddy, generation of helium, 96
— — radium, 99
Sodium in rivers, 53, 64
— in ocean, 53, 64
— in igneous rocks, 67, 71
— in sediments, 67
— age of ocean, 64
— wind-borne, 66
— in sewage, 66
Solar system, origin of, 23 _et seq._
Solar constant, 113
Sollas, thickness of sediments, 76
— age of earth, 86, 87
— age of oceans, 62, 63
— biology and time, 21
— glacial retreat, 43
Steno, 5, 6
St. Meyer and Hess, heat output of radium, 101
Strutt, determination of radium, 105
— radium in rocks, 129, 130
— rate of generation of helium, 139
— leakage of helium, 149
— accumulation of helium, 154-157
Sun, origin of, 25
— helium in, 95, 117
— radium in, 117
— temperature of, 119
— duration of heat of, 12, 14, 112, 114, 120
Suzuki, age of earth, 128
Temperature—gradient of earth’s crust, 122
— due to radium, 128, 132
Thermal conductivity of rocks, 123
Thomson. _See_ Kelvin
Thorianite, generation of helium by, 139
Thorium, discovery as a radio-element, 92
— family of elements, 100, 190
— end product of, 100
— heat output of, 131
— distribution of, in rocks, 131
Tidal retardation, 13, 26, 27
Transformation, radioactive, 97, 98
— end products of, 100
Unconformities, 160
Underground temperature, 12, 13, 122-8
Uniformitarianism, rise of, 7, 9
— criticised, 12, 78, 174
Uraninite, generation of helium by, 139
— lead-ratio of, 151, 158-62
Uranium, atomic weight of, 142
— discovery as a radio-element, 92
— phosphorescence of salts 91, 92
— range of α-rays from, 178
— family of, 100, 190
— end products of, 100, 140-142
— generation of radium from, 99
— — helium from, 142
— — lead from, 142
— heat output of, 116, 131
— half-life period of, 179
— time-average of, 143, 179-182
Uranium-bearing minerals—
Llano Co., 151, 152
Connecticut, 158, 159,
Carolina, 159, 160
S. Norway, 161, 162
Brevig, 163, 164
Mozambique, 153, 160
— alteration of, 150-153
Ussher, chronology of, 3, 10
Van Hise, 88
Velocity of α-particles, 177
Watts, marine erosion, 58
— cycle of deposition, 85
Weathering of rocks, 48, 49
— of minerals, 150
Wilson, W. E., sun’s heat, 116
Zircon, helium-ratio in, 156
— lead-ratio in, 160, 164
Zoroaster, chronology of, 3
WILLIAM BRENDON AND SON, LTD.
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