|Research Communications NETWORK
[This review is based upon a series of telephone interviews with
Robert V. Gentry, as well as the available technical literature.]
Glossary of Technical Terms
A parent radioactive atom decays into a daughter
various ways, one of which is by the emission of an alpha particle
from the parent atom's nucleus. Numerous types of radioactive
atoms occur in nature, but only three are the initiators of a decay
series: uranium-238 (238U); uranium-235 (235 U);
and thorium-232 (232Th).
(The numerical superscript signifies how heavy the element is.
Isotopes of the same element have different weights but nearly
identical chemical behavior—as for example (238U) and (235U). An
alpha particle has a weight of 4.)
Each of the three decay-series initiators decays, by a chain of
steps, into lead. For example, the alpha-decay steps in the 238U
series are the following (steps not involving alpha-decay are not
|238U ||→|| 234Th
||232Rn ||→|| 218Po
|234U ||→|| 230Th
||218Po ||→|| 214Pb
|230Th ||→|| 226Ra
||214Po ||→|| 210Pb
|226Ra ||→|| 222Rn
||210Po ||→|| 206Pb
Similarly, 235U decays by a different series of steps to 207Pb,
and 232Th decays to 208Pb. Note that while all the series end up
with lead, each one results in a different isotope of lead.
The half-life of a given type of radioactive atom is the time
during which half the atoms in any collection will decay. The half-life
of 238U is 4½ billion years. Half-life, decay rate, and decay
constant are closely related quantities. If we assume that the
decay rate has not changed over geologic time,* and if we
measure 1) how much of a parent in a rock has decayed into its
daughter; and 2) the current rate of this decay, then we can, it is
generally believed, assess the date when the parent was
incorporated into the rock—that is, the date when the rock was
formed. In the case of Earth's oldest rocks, this date (some 3½
billion years ago) is thought to be the time when the molten Earth
first cooled down sufficiently for rocks to solidify from the
*Numerous other assumptions and technicalities also come into
- Current physical laws may not have governed the past.
- Earth's primordial crustal rocks, rather than cooling and solidifying over millions or billions of years, crystallized almost instantaneously.
- Some geological formations thought to be one hundred million years old are in reality only several thousand years old.
Grant these propositions and—any researcher will tell you—the
entire structure of the historical natural sciences would dissolve into
formlessness. Few certainties would remain. Yet these very
possibilities (and others equally disintegrative) have been suggested in a
remarkable series of papers published over the past several years in the
world's foremost scientific journals—Nature, Science, and Annual
Review of Nuclear Science, among others. Nor has this assault upon
orthodoxy elicited a vigorous counterattack: the research results published
to date have been so cautiously and capably elaborated, and
evidence so thoroughly piled upon evidence, as to forestall any outcry
by those whose scientific sensibility may have been outraged. While
some investigators appear finally to be arming themselves for combat,
the issue has not yet been joined.
It was over a decade ago that Robert V. Gentry, puzzling over
questions about the Earth's age, directed his attention to an obscure and
neglected class of minute discolorations in certain minerals. He has since
examined more than 100,000 of these "radiohalos," and without doubt
stands as the world's leading authority on the subject. As an assistant
professor of physics at Columbia Union College (Takoma Park,
Maryland), he has brought to bear upon the halos an array of sophisticated
instrumentation such as few researchers ever have the privilege to
wield. As a result, he has converted the entire field of radiohalo research
into an exact science, transmuting the microscopic spheres of mystery
into rich mines of exciting and challenging information.
RADIOACTIVE HALO (or RADIOHALO): "In some thin samples of
certain minerals, notably mica, there can be observed tiny aureoles of
discoloration which, on microscopic examination, prove to be concentric
dark and light circles with diameters between about 10 and 40μm
[a lone micrometer is one-millionth of a meter] and centered on a tiny
inclusion. The origin of these halos (first reported between 1880 and
1890) was a mystery until the discovery of radioactivity and its
powers of coloration; in 1907 Joly and Mugge independently suggested
that the central inclusion was radioactive and that the alpha-emissions
from it produced the concentric shells of coloration. . . . halos command
attention because they are an integral record of radioactive decay in
minerals that constitute the most ancient rocks" (1).
Gentry's studies have led him to the following conclusions:
Some halos ("polonium" halos) imply a nearly instantaneous
crystallization of Earth's primordial rocks: and this crystallization
must have occurred simultaneously with the synthesis/creation of
Some halos correspond to types of radioactivity which are
Whereas radiohalos have been thought to afford the strongest
evidence for unchanging radioactive decay rates throughout geological
time (and these rates enable scientists to determine rock ages), in
actuality the overall evidence from halos requires us to question the
entire radioactive dating procedure: something appears to have
disrupted the radioactive clocks in the past.
Halos in coal-bearing formations that are conventionally
thought to be 100 to 200 million years old suggest these strata to be
only several thousand years old. Further, the time required for coal
formation is much less than previously thought.
Taken together, these conclusions point to one or more great
"singularities" in Earth's past—events or processes that are
discontinuous with the rest of history, unique occurrences that
critically affect the data we now have. If we attempt to interpret
these data solely in terms of current processes, we go astray.
In this report we will discuss only those researches leading to
conclusion (1), reserving the rest for a subsequent report.
THE CONSERVATISM OF SCIENCE
January 29, 1975
You ask for my opinion of Dr. Robert Gentry's work on
pleochroic polonium halos. I spent a number of hours reviewing
this fascinating work with him some weeks ago. I was impressed
with the clarity of the evidence for "anomalous halos"—that is,
cases where there are rings indicating the presence of some
members of the normal radioactive decay chain without the other
members of the family tree that normally are present, that
normally do show up in rings of their own, and that have to be
there on present views of the radioactive decay chains involved. If
the evidence is impressive, the explanation for it is far from clear.
I would look in normal geologic process of transfer of materials
by heating and cooling; in isomeric nuclear transitions; and in
every other standard physical phenomenon before I would even
venture to consider cosmological explanations, let alone radical
cosmological explanations. To explore all the avenues that need
exploring would take months, not the few hours I was privileged
to spend in Dr. Gentry's company. A few days ago I reviewed this
work, all too briefly, with Dr. G. Wasserburg of Cal Tech, who is
an expert in the radioactive dating of rocks, whose opinion would
be much more to the point than mine, especially if he will give it
to you in writing.*
JOHN A. WHEELER
(Professor of Physics,
*Professor Wheeler requested that his letter be printed in full.
Dr. Wasserburg's views have not been obtained.
Many have noted a conservatism in science essential to its orderly
advance: skepticism toward radically new ideas enables scientific
journals to retain focus, prevents anarchic descent into theoretical
chaos, and makes it possible to extend currently reigning theories as
far as they can bear before replacing them with other theories yet
more embracive. A successfully modified, "tested" theory is
preferable to a new "untried" theory. And so scientific knowledge
advances in an orderly fashion, with as few wrong turns as possible.*
[* This conservatism—and its deceptive advantages—will receive continuing
discussion in these newsletters.]
Gentry has so far avoided clashing with this conservatism, chiefly
by concentrating his efforts on publication of data rather than
discussion of their implications—and also by the good fortune that
his work has been slow to draw widespread attention. That is
beginning to change, however. But perhaps the reaction of a number
of prominent physicists to Gentry's work on polonium halos (see
insets on this and the following page) is the most significant gauge of
what will be forthcoming. This reaction is noteworthy both for the
confidence expressed in Gentry's work and for the almost uniformly
conservative—albeit open—stance toward any extrapolations from
the raw data that challenge accepted theory. Of those whose opinions
we sampled, only one seemed to suggest (without wishing to be
quoted) that we not publicize Gentry's work. He felt that the subject
should be "left to the experts," while cautioning that it is too early to
reject the conventional view of Earth's history.
In the end, it is, presumably, the evidence which will decide the
issue. Let us look more closely at the radiohalos themselves.
THE NATURE OF HALOS
If a small grain (inclusion) containing radioactive atoms is
embedded in certain rock minerals, the alpha particles emitted from
the radioactive atoms travel outward from the inclusion and damage
the crystalline structure of the mineral, in time producing the visible
discoloration typifying halos. Since each type of radioactive atom
emits alpha particles with a characteristic energy, and since this
energy determines how far the particle will travel in the host mineral,
the diameter of a halo's rings guides researchers in determining which
radioactive element is responsible for the halo. If the radioactive
element in an inclusion is the initiator of a decay series, then a group
of concentric halo rings results, each ring corresponding to a step in
the decay series, that is, to alpha particles of a particular energy. In
the case of the 238U series, with eight alpha-decay steps, there are five
distinct halo rings (some of the alpha particles are so close together in
energy that their rings are not distinguishable).
The conventional argument drawn from observed radiohalo sizes
is summarized by Struve:
"There is excellent evidence that the rates of radioactive processes
measured in the laboratory at the present time are valid also for the
remote past. If a radioactive element and its decay products are embedded
in a crystal, each alpha particle emitted during disintegration
travels a certain distance that depends only on the rate of that particular
decay step. The more rapid this rate, the greater the energy of the alpha
particles, and the farther they go before being stopped and producing a
color change in the crystal.
A uranium-238 halo (left) and a polonium-210 halo in biotite.
Scale is 1 cm equivalent to 45 μm [in the original publication, ed.].
"Suppose a speck of 238U has remained undisturbed since the
formation of a mineral containing it. Then, because the rate of disintegration
at each successive emission is different, eight concentric rings of
mineral discoloration will be found surrounding the particle of uranium.
These rings . . . have been found in many rocks of different geological
ages, and the diameters of the respective rings are always the same.
"Thus it can be concluded that the rates of disintegration of
uranium and thorium are constant" (2).
As we will learn in a subsequent review, the evidence from halos
has led Gentry in a direction quite opposite from Struve's. But more
than that, Gentry's halo research appears to strike at the roots of
virtually all contemporary cosmologies, posing a fundamental
problem which has so far resisted every effort to solve it in
conventional terms. This is the problem of the polonium halos.
Comments by Leading Scientists
Before the demise of the journal, Pensée, the editor—in
preparation for a planned article on Gentry's work—approached a
number of leading scientists for their assessment of polonium halos.
The following responses were received during the first month or so of
PROFESSOR TRUMAN P. KOHMAN, Department of Chemistry,
Carnegie-Mellon University, Pittsburgh. "I do not believe that
'Gentry's contentions' can be regarded as of 'rather startling nature.'
However, some of his experimental findings (like those of his
predecessors) are quite difficult to understand, and the ultimate
explanations could be interesting and even surprising. Many persons
probably do not take them seriously, believing either that there is
something wrong with the reported findings or that the explanations
are to be found in simple phenomena which have been overlooked or
discarded. . . . I believe it can be said that Gentry is honest and
sincere, and that his scientific work is good and correctly reported. It
would be very hard to believe that all, or any, of it could have been
PROFESSOR EDWARD ANDERS, Enrico Fermi Institute,
University of Chicago. "His [Gentry's] conclusions are startling and
shake the very foundations of radiochemistry and geochemistry. Yet
he has been so meticulous in his experimental work, and so restrained
in his interpretations, that most people take his work seriously.
. . . I
think most people believe, as I do, that some unspectacular
explanation will eventually be found for the anomalous halos and that
orthodoxy will turn out to be right after all. Meanwhile, Gentry
should be encouraged to keep rattling this skeleton in our closet for all
it is worth."
DR. EMILIO SEGRE, Istituto Di Fisica "Guglielmo Marconi,"
Università Degli Studi, Rome. "The photos [of radiohalos] are remarkable,
but their interpretation is still uncertain."
PROFESSOR FREEMAN DYSON, Institute for Advanced Study,
Princeton. "Supposing that the results of Gentry are confirmed, what
will it mean for theory? I do not think it will mean any radical changes
in geology or cosmology. It is much more likely that the explanation
will be some tricky point in nuclear physics or nuclear chemistry that
the experts have overlooked. That is of course only my personal
opinion and I am accustomed to being proved wrong by events. (I just
lost a $10 bet that Nixon would be in office till the end of 1974. I will
be glad to lose this one too.)"
ACADEMICIAN G. N. FLEROV, Joint Institute for Nuclear
Research, Moscow. "We made sure that [Gentry] carried out his
investigations very thoroughly. . . .
Therefore his data deserve serious
attention. . . . It is not excluded that [polonium halos] have been
formed as a result of the extremely rare combination of geochemical,
geological and other conditions, and their existence does not contradict
the logically grounded system of concepts involved in the history of
DR. PAUL RAMDOHR, Emeritus Professor of Mineralogy,
Heidelberg University, Heidelberg. "The very careful and timetaking
examinations of Dr. Gentry are indeed very interesting and extremely
difficult to explain. But I think there is no need to doubt 'currently
accepted cosmological models of Earth formation'. . . .
Anyhow, there is
a very interesting and essential question and you could discuss it,
perhaps with cautious restrictions against so weighty statements like
the one above in quotes. It would be interesting and good if more
scientists would have more knowledge of the problems."
PROFESSOR EUGENE P. WIGNER, Department of Physics,
Rockefeller University, New York. "Even though I know Dr. Gentry
personally, I am not sufficiently familiar with his scientific results to
be able to judge them. Personally, however, I have a very high regard
DR. E. H. TAYLOR, Chemistry Division, Oak Ridge National
Laboratory, Oak Ridge, Tennessee. "I can attest to the thoroughness,
care and effort which Gentry puts into his work. . . .
In a general way
these puzzling pieces of information might result from unsuspected
species or phenomena in nuclear physics, from unusual geological or
geochemical processes, or even from cosmological phenomena. Or
they (or one of them) might arise from some unsuspected, trivial and
uninteresting cause. All that one can say is that they do present a
puzzle (or several puzzles) and that there is some reasonable
probability that the answer will be scientifically interesting."
The last three alpha decay steps in the uranium-238 decay series
(see glossary above) involve the successive decay of polonium-218
(218Po), polonium-214 (214Po), and
polonium-210 (210Po). In contrast
to the decay of the parent uranium, these steps occur very quickly;
the half-lives of the three forms of polonium are 3.05 minutes, 164
microseconds, and 140 days, respectively. Polonium, therefore, is not
thought to be observed in nature except as a daughter product of
uranium and thorium decay.
That is where the enigma begins. For Gentry has analyzed
numerous polonium halos possessing, in some cases, the rings for all
three polonium isotopes; in other cases the rings
for 214Po and 210Po;
and in other cases, the ring for 210 alone—but none of these halos
exhibits rings for the earlier uranium-238 daughters. These halos are
evidence for parentless polonium, not derived from uranium.*
[* Gentry has also found halos with rings from polonium-218, -214,
or -210, combined with a ring from polonium-212 which is in the
thorium decay series. This last form of polonium is also parentless— that
is, there are no halo rings for thorium itself or its other daughters.]
But the question then arises, How did the polonium inclusions
ever become embedded in the host rocks (more specifically, in Earth's
oldest—Precambrian—rocks)? On the conventional view, these rocks
slowly cooled and crystallized out of the primordial magma (molten
rock) over millions of years. Under such circumstances, any polonium
(with its extremely short half life) that was incorporated into the
solidifying rocks would have completely decayed long before the
crystalline rock structure was established. No halos could have
formed, for they consist precisely of radiation damage to this
crystalline structure. Polonium rings should exist only in conjunction
with the other uranium series rings. But since the actual halos were
caused by parentless polonium, they require nearly instantaneous
crystallization of the rocks, simultaneously with the synthesis or
creation of the polonium atoms.
Gentry, well aware that this conclusion is unthinkable to most,
has buttressed it with impressive experimentation:
fission track and neutron flux techniques (3) reveal no uranium in the
inclusions that could have given rise to the polonium—a conclusion
more recently confirmed by electron microscope x-ray fluorescence
spectra (4); fossil alpha recoil analysis (3) demonstrates that neither
polonium nor other daughter products migrated from neighboring
uranium sources in the rock, which agrees with calculations based on
diffusion rates (5); ion microprobe mass spectrometry yields extraordinarily
high 206Pb/207Pb isotope ratios that are wholly inconsistent
with normal decay modes (6), but which are exactly what one would
expect as a result of polonium decay in the absence of uranium.
To date there has been only one effort (7) to dispute Gentry's
identification of polonium halos. As it turned out (4), that effort might
better never have been written, the authors having been impelled more
by the worry that polonium halos "would cause apparently
insuperable geological problems," than by a thorough grasp of the
evidences. Challenges to Gentry's interpretation of the polonium
halos have been more noteworthy. English physicist J. H. Fremlin
wrote in Nature (November 20, 1975) that "The nuclear geophysical
enigma of the 210Po halos is quite fascinating, but the explanation put
forward is not easy either to understand or to believe." Fremlin proposed two
Geologic transfer. If there are uranium inclusions reasonably close
to polonium halos, then it is possible that one or more of the uranium
daughter products migrated from the uranium site to a new location,
where subsequent decay gave rise to the polonium halo. Since the
daughter products have much shorter half-lives than uranium, we
would not expect to find any quantity of them remaining at the site of
the halo. The polonium would therefore appear to be "parentless."
The difficulty with this view is that transfer of uranium daughters in
minerals occurs so slowly that the daughters would decay long before
they could migrate any significant distance (3, 5).
If the sophisticated experimentation cited above proved telling
against the transfer hypothesis, Gentry and several co-workers
delivered a yet more conclusive blow in a very recent paper:
polonium halos derived by geologic transfer from uranium sources
have now actually been found in coalified wood deposits (8). Their
presence here was to be expected: prior to coalification the wood was
in a gel-like condition permeated by a uranium-bearing solution. Such
a material "would exhibit a much higher transport rate as well as
unusual geochemical conditions which might favor the accumulation
of 210Po"—quite different from the situation in mineral rocks. Further,
of these uranium-derived polonium halos, none were found due to
218Po, and only three could conceivably (but doubtfully) be attributed
to 214Po, in contrast to numerous 210Po
halos. The half-life of 210Po
we will recall, is 140 days, whereas the half-life of those forms of
polonium which failed to generate halos in the coalified wood is a few
minutes or less. So even under the ideal conditions in this wood, the
short-half-lived 218Po and 214Po were not able to migrate rapidly
enough from the parent uranium to form "parentless" halos. Clearly,
then, such migration could not account for the 218Po
and 214Po halos
Gentry has found in Precambrian minerals, where the diffusion rate is
very much lower even than in wood (5).
Isomer precursors. Two atoms with identical nuclear composition
but different radioactive behavior are termed "isomers." For example,
212Po (in the thorium decay series) decays to 208Pb by emission of an
alpha particle with an energy of 8.78 MeV. However, about one out
of every 5500 212Po atoms emits an alpha particle with a much higher
energy of 10.55 MeV. These rarely occurring, higher-energy 212Po
atoms are isomers, and they are apparently explained by some
variation in nuclear structure. The suggestion has been made,
therefore, that polonium halos may result from the presence of
heretofore unknown isomers which are long-lived and which decay*
into polonium. These isomers ("precursors" of polonium) would
circumvent the cosmological problem caused by the short-half-life
[* by beta-emission]
However, not only are such isomers unknown, but a careful search
has revealed the presence of no elements which might qualify as the
required isomers (4, 5). "Experimental results have ruled out the
isomer hypothesis" (5).
And so we have Gentry's conclusion in his reply to Fremlin:
"But if isomers and uranium-daughter diffusion do not produce
polonium halos in rocks, we are left with the idea that polonium halos
originate with primordial Po atoms just as U and Th halos originate
with primordial 238U and 232Th atoms. . . .
Carried to its ultimate
conclusion, this means that polonium halos, of which there are
estimated to be 1015 [one million billion] in the Earth's basement
granitic rocks, represent evidence of extinct natural radioactivity, and
thus imply only a brief period between 'nucleosynthesis' [creation
of elements] and crystallization of the host rocks" (5). In plainer
terms, these rocks must have formed almost instantaneously upon the
synthesis of the elements comprising them.
Gentry believes the evidence points to one or more great
"singularities" that have affected Earth in the past, representing
physical processes which we do not now observe. If this is so, then
attempts to define these processes in conventional terms will prove
fruitless, and the span represented by geologic time is a wide open
question. Further (as we will explore in a subsequent review), Gentry
concludes that the most recent "singularity" may have occurred only
several thousand years ago. And he finds compelling reasons to question
the entire radioactive dating scheme which undergirds our
concept of geological time.
Gentry realizes that he still must reckon with the conservatism of
science. While his experimental work has been impressive, few would
yet concede that it is impregnable, or that his explanations are the
only possible ones. As Wheeler remarked:
"If the evidence [for the polonium halo] is impressive,
the explanation for it is far from clear. I would look in
normal geologic process of transfer of materials by heating
and cooling; in isomeric nuclear transitions; and in every
other standard physical phenomenon before I would even
venture to consider cosmological explanations, let alone
radical cosmological explanations."
While the evidence does not seem to favor the specific
mechanisms Wheeler suggested in early 1975, Gentry can be sure
that, in pressing his own decidedly radical explanations, the sound
and fury lie yet before him.
R. V. Gentry, Annual Review of Nuclear Science 23 (1973), p.
O. Struve, Sky and Telescope 18 (June, 1959),
R. V. Gentry, Science 160 (June 14, 1968),
R. V. Gentry, Science 184 (April 5, 1974), pp. 62-66.
R. V. Gentry, Nature 258 (November 20, 1975),
R. V. Gentry, L.D. Hulett, S.S. Cristy, et al., Nature 252
(December 13, 1974), pp. 564-66.
C. Moazed, R.M. Spector, and R.F. Ward, Science 180
(June 22, 1973), pp. 1272-74.
R.V. Gentry, W.H. Christie, D.H. Smith, et at., Science
194 (October 15, 1976), pp. 315-18.