Origins 19(2):87-90 (1992).
LITERATURE REVIEW
THE AGE OF THE EARTH. 1991. G. Brent Dalrymple. Stanford University Press. Stanford, California. 474 pp. Cloth, $49.50.
There has been a long-standing need for a convenient compilation of
the radiometric data from which conclusions have been drawn concerning the length of time
planet Earth and other components of the Solar System have been in existence. The Age
of the Earth meets this need more than adequately. The author is Research Geologist
at the U.S. Geological Survey, Menlo Park, California, and is preeminently qualified to
give a comprehensive, authoritative, and readable treatment of the topics he addresses. In
his Preface he states that the book was "written for people with some modest
background in science, ... [to be] useful and informative to those without a deep knowledge
of geology or physics." The book provides valuable resource material for individuals
who make a professional-level witness for a creationist viewpoint, although the author's
analysis of data is from a purely secular, uniformitarian approach that dismisses concepts
of supernatural and revelation as purely human and non-authoritative.
Technical terms and concepts are explained within the text so that the
treatment is understandable to the non-specialist. A 14-page glossary provides additional
assistance. The treatment is well-illustrated by 15 half-tones, 14 maps, and 98
high-quality line drawings. Many readers will not be interested in the extensive
mineralogical and geological detail in some sections of Dr. Dalrymple's treatment, but the
persistent reader will be well rewarded. Citations to the original supporting scientific
literature are given within the text. Readers who wish to investigate any topic more
deeply have 37 pages of references for these citations. Each technical chapter concludes
with a summary, and the final chapter is a summary of the entire book.
Chapter Two reviews the estimates for the age of planet Earth that were
made before the radiometric era (before circa 1950), including those based on the
Pentateuch. A tabulation of these estimates (Table 2.1) covers four pages.
The third chapter is a tutorial on the use of the various radiometric
daughter/parent pairs for data from which age estimates may be made. These estimates cover
primary age, age since a metamorphism, and ages over the range between these limits. To
the evidence given for the constancy of radioisotope decay rates, I can add that provided
by radiohalos (Brown 1990). I recommend this chapter to anyone who is looking for a
relatively quick and easy way to become familiar with the rudiments of radioisotope
dating. Toward the end of the book (Chapter 7), an entire chapter is devoted to the use of
lead isotope ratios as indicators of time spans.
It is unfortunate that the author's treatment of isochrons (linear
sequences of a group of associated daughter/parent isotope ratios) does not explain how
these sequence plots could also be interpreted as mixing diagrams, rather than a daughter
isotope accumulation plot (isochron). This possibility has been used by some apologists in
efforts to discredit use of radioisotope data as an indication of real time.
If there is a non-uniform distribution of parent isotope among a group
of related samples, a plot of daughter concentration against associated parent
concentration (or more commonly, plot of the ratios of daughter and parent isotopes to a
reference isotope) will be a straight line if the daughter concentration represents growth
by radioactive decay of the parent. For a common time lapse the amount of daughter
difference between any two samples will be proportional to the amount of parent
difference, hence the term isochron (equal time). An identical plot can be produced by an
incomplete mixture of material from two sources that had differing parent and/or daughter
concentrations. Such a plot would be merely a mixing line that has no relationship to the
time at which the mixing occurred. But the upper end of the line of data terminates at or
points to the daughter/parent ratio which specifies a radioisotope age for one source, and
the lower end terminates at or points to the daughter/parent ratio which specifies a
radioisotope age for the other source. If the ratio of parent to excess of daughter above
the amount of daughter specified by cosmic isotope abundance ratios is the same for each
of these sources, an isochron interpretation assumes the daughter excess accumulated since
mixing, and hence specifies time since the mixing that produced the common suite
of samples. A mixing line interpretation, however, gives the age of the components
of the inhomogeneous mixture, but provides no indication of the time since mixing
occurred.
Interpretation as a mixing line is clearly indicated if the best
straight-line fit to the data points intercepts the daughter isotope axis at a point
significantly different from the cosmic ratio of the daughter isotope (ratio
characteristic of minerals which have no indication of having been associated with the
parent element). In such cases the data set limits for the radioisotope age which
characterizes each component of the mixture.
Mixing line interpretation is a valid option regardless of where the
line intercepts the daughter isotope axis. In any case a mixing line interpretation
provides no escape from a real time significance of radioisotope daughter/parent ratios.
Linear plots of daughter versus parent for some inhomogeneous sets of samples may be
expected to represent isochron development following initial formation by mixing. Isochron
development gives a counterclockwise rotation to the initial mixing line, but leaves no
basis for determining how much time has elapsed since the mixing process.
The Age of the Earth makes two major contributions. One is a
convenient collection of radioisotope data for the lowest rocks in the geological sequence
of Earth's crust (Chapter 4), rocks from the Moon (Chapter 5), and meteorites (Chapter 6).
The other major contribution is ready access to analysis of these data. Any reader will be
impressed at the frequency with which the figure 4.56 billion years appears from a wide
range of independent radioisotope techniques applied to a wide range of samples. How a
creationist accommodates to this evidence will depend on whether he/she considers it to be
a consequence of the way God has managed/maintained the Universe, or a design
characteristic expressed at initial creation.
Dalrymple makes a good case for an age of about 4.5 billion years for
the material of which the earth, moon, and meteorites are composed. He evidently believes
that he has thoroughly discredited special creationism. His treatment in The Age of
the Earth has made it much more difficult to plausibly explain radiometric data on
the basis of a creation of the entire Solar System, or the physical matter in planet
Earth, within the last few thousand years. In my opinion, the defense of such a position
is a losing battle.
However, the data presented by Dr. Dalrymple are not incompatible with
a model which allows for most of the Solar System to have come into existence about 4.5
billion years ago, the creation of life on planet Earth within the last 10,000 years, and
a subsequent reorganization of the planet's surface by a cataclysm in which there was
water burial of a vast number of organisms.
The final technical treatment in the book (Chapter 8) completes age
considerations with a summary of speculative models concerning the ages of stars and
galaxies. Readers who follow details carefully should correct Table 8.5 on p. 388 to
specify 1/137.88 for R of 235U/238U.
In concluding this review, I should say that in my opinion it is both
incorrect and inadequate to model the physical features of the universe on the basis of
natural evolution from an unexplainable initial "Big Bang"; and that it is
equally incorrect to ignore the evidence for physical process and change. The basic data
and their implications as given in The Age of the Earth present no conflict with
biblical testimony as long as the creation account is interpreted strictly in accord with
the definitions given in Genesis 1:8-10, and if the radioisotope ages of material that
encloses or overlies fossils are recognized as having no more relationship to fossil age
than similar data for a modern cemetery, or a community buried by a landslide, have to the
dates of the interments therein.
ACKNOWLEDGMENT
Appreciation is due for the contributions of Dr. Paul Giem in the preparation of this review.
REFERENCE
All contents copyright
Geoscience Research Institute. All rights reserved.
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