The Age of the Earth
G. Brent Dalrymple
Preface - tells the tale of him being involved in the Creation Science trials, first in California, then in Arkansas and Louisiana. The writing of "Radiometric Dating, Geologic Time and the Age of the Earth: A Reply to Scientific Creationism" This was intended to be a chapter in a book that never got finished, but was published through USGS as an open document. Notes that he was witness along with Francisco Ayala, Stephen Jay Gould, and Harold Morowitz. He does not include a discussion of Creation Science in this book because "The creationist's 'scientific' arguments for a young Earth are absurd, and I and other authors have dealt with them at length elsewhere. " pg x One thing that hurts here is that he lumps all "creationists" in with Morris and company, hence giving insight into how much the likes of Morris have hurt the rational dialog between science and faith.
Ch 1 Introduction
Tries to set a general framework of the standard model of the universe, starting with big bang and using a scenario like Weinberg's First Three Minutes. I have heard Dalrymple spoken of in glowing terms, and I continue to see him as a great contributer to this subject. But I am surprised at some of the inaccuracies in this chapter. Some may be due to the fact that we have learned a lot since 1991, but he quotes the size of the Milky Way as 30,000 light years, off by a factor of three from the 100,000 light years given by astronomy books, and that was well known in 1991. Maybe he got mixed up between light years and megaparsecs. He also quotes the number of stars in the Milky Way as a hundred million, when the accepted figure is more like 100 billion! A factor of 1000 error from someone who's reputation implies conscientious accuracy?!
Ch 2 Early Attempts: A Variety of Approaches
p18 "Not until the Enlightenment did observation and secular reasoning become widely accepted as an alternative to the Christian interpretation of nature, and modern science was born. But the habits of centuries were difficult to overcome." This is about as outrageous a caricature of the relationship of Christianity to modern science as I have ever seen. To be sure, his view is skewed by having dealt with the likes of Morris and Gish so much, but there is still no excuse for being this ignorant of the role that Christian faith played in the beginning and advance of modern science.
p14-15 Table of pre-1950 dates
p19 Ussher and Biblical chronology
p25 Decline of the Sea. "decline" means loss of water into the "vortex' postulated by a cosmological model of that day. The finding of sea shells high in the mountains was taken as evidence that seas had dropped over the ages - in print 1748. Based on an extrapolation of the amount of sea level drop, 6000 ft or 3-4" per century gave 2.4billion years So he projected 2 billion for beginning. Notable for usig physical observations to project age.
p28 Newton proposed cooling studies that projected about 50,000 yrs in 1687
p29 Businessman Buffon in 1778 projected 75000 years
p30 William Thomson (Lord Kelvin) , bio on 31, most honored British physicist
p33 Kelvin's infall model
p38 98 million years using thermal conductivity, guess of 3870 initial
p40 King, geologist, 1893 paper
p41 Combined with Kelvin data projected 24 million
p47 Convection in ocean floors, convection more important than conduction because convection brings is up to the thin crust and then it is conducted out through the crust. Also point that 2/3 of the heat is from radioactive decay.
p47 George Darwin's moon model projects 56 million year age.
p52 The salt clock
p55 Figures on salt, volume of oceans, influx led to 100 million year age.
p59 Sediment accumulation still gives about 100 million years
p60 Time scales
p69 Early radiation methods, Roentgen, Curie, Becquerel
p70 Radioactivity history
p71 Rutherford proposes geologic clock
p71 Uranium-helium dating about 500 million years.
p72 Rutherford proposes U-Pb methods
p74 Table of Pb/U ages ).4 to 2.2 billion years, 1907-1911, first evidence of age in the billions of years.
p76 Henry N. Russell, about 4 billion in 1921, range 2-8 billion years.
p78 Holmes summary table.
Ch 3 Modern Radiometric Methods.
p80 Table of isotopes used
p80 Radioactivity, Nature's Timepiece, chk references on p80
p81 Used in dating beta minus, electron capture, alpha
p82 Graphic on p82, might have a go at a more info-rich version of it for hyperphysics
p86 radiometric age equation
p87 Why decay constant unaffected
p87 3rd Paragraph "This is the reason why nuclear reactors and powerful particle accelerators are required to penetrate and make changes in atomic nuclei. Except in nuclear reactions, such energies are generally unavailable in natural processes such as those that form, change, and destroy rocks on the Earth and in the Solar System."
p87-88 Excellent examples of why the decay constant is unaffected by the extremes of macroscopic environment - bomb, liquid H temperature.
p88 Possible <0.01% effect for beta emitter from chemical effects in atom, but has never been approached in laboratory. For c14, Co60 and Ce137 there are possible deviations from ideal random distribution, but no detected change in decay constant.
p89 pred that 7Be might undergo induced changes in decay rate. Decay rate in 7Be metal 0.013 to 0.015% higher than in BeO. Maximum difference found between two Be compounds is 0.18%. Also measurable pressure effect on decay of BeO.
p89 Measurable effects on decay of internal conversion, but that is not used in radioactive dating.
p90 K-Ar, 40K 1.25Gy
p92 Natural abundance table
p93 Eq 3A, K-Ar age equation, K-Ar igneous rock, discussion of applications.
p95 Sm-Nd, Lu-Hf and Re-Os
p97 adv of Sm-Nd method
p99 U-Th-Pb method
p101 207Pb/206Pb method
p102 Disc of age diagnostic diagrams, clear discussion, add to my isochron treatment.
p102-109 Excellent discussion of isochrons
p108 Example of destroying straight line when material is lost, i.e., not a closed system. Uses the term "isotropic homogenization".
p109 "isochron method is self-checking."
p109 40K/39Ar age spectrum and isochron
p111 Different isochrons
p112 High temperature plateau age
p115 U-Pb concordia and discordia
p117 Pb is easily lost by heating, but that does not fractionate the isotopes in the remaining lead because they are chemically identical and their masses are very nearly the same.
p119 zircon comes through again as a basis for concordia-discordia because its initial lead content is nearly zero.
p119 zircon useful in rocks of complex history
p119 Pb-Pb isochron, Pb compared to nonradiogenic 204Pb
p120 St Serverin meteorite
p122 Halflives 2% or better
p123 Isotopic ratios a few tenths of a percent.
p128 Oldest earth rocks 3.8-3.9 Gy
p129 geology of old archaen rock, lots of mineral names.
p140-141 Table of old rocks
p143 Rb/Sr isochron 3.66 Gy
p144 Concordia-discordia diagram
p146 SmNd isochron
p149 RbSr isochron, these last three with the same rocks.
p153 RbSr 3.55Gy
p158 RbSr 3.48 Gy
p160 Concordia-discordia 3.3, 3.59
p160 Morton gneiss
p161 Watersmeet U-Pb plus Nd/Nd
p174 U-Pb concordia-discordia
p192 Zircon 4 - 4.3Gy
Ch 5 Moon Rocks
p194 Rocks majority 3.2-4Gy, but oldest 4.5 Gy
p194 Models of moon formation: fission, capture, formation with Earth as double, and collision
p197 Oxygen isotopic ratios for Earth and Moon and differentiated meteorites. Identical, but differ from more primitive meteorites.
p198 Collision hypothesis
p202 lunar maria 3.0-3.9 Gy basalt
p203 highlands 3.8-4 Gy, few near 4.5 Gy
p203-210 Good overview of moon
p211 Core by Apollo 15 showed 42 distinct layers
p212 Moonrock table, 9 missions, 382 kg of samples
p213 Similarities and differences from earth rock
p214 Table and comparison
p218 Geohistory of moon
p227 Graphs of ages
p231 Age table
p232 RbSr, Sm/Nd isochrons
p234 Highland data, a couple sitting on 4.5 Gy
p246 Sm Nd 4.26 isochron, use for brief treatment of Sm Nd, Also Sr Rb on moon 4.51, might be good illustration.
p256 Summary 4.5 Gy, 3.8 - 4.5 bombardment, Timescale volcanism 3.1-1, inactive for 1 Gy.
p258 Historical meteorites
p260 Several thousand n elliptical pattern, April 26, 1803, estimate of mass
p262 Rate diagram
p274 Origin, 275 diagram
p283 Lunar highland meteorite Antarctica
p283-284 SNC from Mars
p286 Bar graph, lots around 4.5 Gy
p287 Table, 4.5-4.6 Gy
p289 SNC meteorites 1.22-1.34 probably from Mars
p293 Summary samples
p299 St Severin meteorite
p304 4.4-4.6 and 4.5-4.6 Gy range
Ch 7 Isotopes of Lead: The Hourglass of the Solar System
p305 How old is Earth? 4.54 Gy from lead isotopes, Holmes-Houtermans model
p310 History of lead application
p311 Ivigtut, Greenland standard, very low radiogenic lead, so used to determine constants a0, b0.
p321 Using meteorite lead as standard led to >4Gy ages. Preceding material uses old earth deposits. This begins the process of zeroing in on current age figures and evaluation of the assumption of common lead composition.
Arguments for connection between meteoritic lead and young terrestrial lead. Canyon Diablo meteorite. CC Patterson 3 stone + 2 iron - data on an isochron at 4.55 +/-0.07 Gy. Graph Fig 7.6 p321, compare to modern ocean sediment. Modern values reduce this age to 4.48 Gy. Refers to the time of initial formation and differentiation of the meteorites. .
The Pb-Pb isochrons turn out to be the most precise and reliable dating method provided you have a reliable primeval reference. The meteorites provide this reference based on developed evidence that the earth leads and meteoritic leads have a common origin.
The evidence chain for Pb-Pb made a major step with Patterson's work in 1956 which used the Canyon Diablo Henbury meteorite as a reference. He used three stone and two iron meteorites and got an impressive isochron including all of them. Then he showed that ocean sediment iron felt right on that line. The age of 4.48 Gy was in agreement with K-Ar and Rb-Sr ages. The diagram is on pg 321.
p323 Canyon Diablo on 263, 318f, 321-45, 354f
a0 =9.307, b0=10.294 Table of others, "generally accepted value for primeval lead in the solar system." On p318 values for constants, values for Pb and U, Troilite contained the lowest Pb ratio and exceedingly low U, discussion 3rd paragraph of 318.
p327 reproduce figure 7.8 for Allende. Maybe 329 if I can understand it.
p 329 Data. Update Canyon Diablo with numbers, refer to Allende, maybe comments from summary.
p331 Slight differences K-Ar, Pb-Pb, Rb-Sr might be differences in early solar formation processes.
p332 Meteorites 4.55 +/- 0.02 from Pb-Pb
p333 Terrestrial connection with meteorites
p343 Check out value 4.54 Table 7.6
p355 Summary significant - highlighting Canyon Diablo
p356 4.52-4.56 Gy with 4.54 being probably the best value using four oldest conformable lead ores to 1% accuracy or better. Consistent with meteorites and the oldest lunar rocks.
p356 Congruency point of four oldest conformable lead ores. Uses Canyon Diablo. See p347 for more detailed curve on 347, but he points instead to another congruency model. Assume one parameter and calculate the other for three different samples and see if there is a common point between them. P346 for 4.54 mu=8. "conformable" is on p450 in glossary -sedimentary ore formed by precipitation that conforms to the geometry of the sedimentary rocks with which it is interbedded.
p376 Discussion of missing nuclides.