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Porvaznik: I shall now discuss the scientific evidence for an ancient earth, then I will cover the evidence for macroevolution.

See also Part 2: The Scientific Evidence for Evolution

The Evidence for an Old Earth

There are various scientific evidences for an ancient earth and/or solar system and universe (distance from the stars, speed of light, evidence from astronomy and physics, etc), but I will concentrate on the direct geological evidence: the material and rocks of the earth, the moon, and meteorites, and the various methods of radiometric dating that geochronologists use to determine their ages. This is considered the most powerful evidence for an ancient earth (c. 4.5 billion years old) and I will give a brief summary of the authoritative work on the subject: The Age of the Earth (Stanford Univ Press, 1991) by G. Brent Dalrymple which covers this material in much detail.

 

 

The Case of the Missing Nuclides

Before we discuss the specifics of radiometric dating, it would help to talk about some of the elements involved. There is a substantial literature on the abundance of various elements in the cosmos, drawing upon studies of the earth, the moon, and meteorites. From this list we can extract information about which of the isotopes of the various elements, known as nuclides, are found in nature at detectable levels. The half-life of an element (if you remember from your high school or college chemistry courses) is the time it takes for one-half of the atoms of an unstable element or nuclide to decay radioactively into another stable element or nuclide. When we strike from the list every nuclide that is continually produced by natural processes, we are left only with those that persist from the date of the formation of our solar system (from Kenneth Miller, page 69-72). What does this list tell us? (See an online periodic table of elements here)

Listing of Persistent Nuclides by Half-Life

[ From Dalrymple (page 377), also Kenneth Miller (page 71) ]

Nuclide Half-Life Found in Nature?

50V 6.0 x 10^15 yes

144Nd 2.4 x 10^15 yes

174Hf 2.0 x 10^15 yes

192Pt 1.0 x 10^15 yes

115In 6.0 x 10^14 yes

152Gd 1.1 x 10^14 yes

123Te 1.2 x 10^13 yes

190Pt 6.9 x 10^11 yes

138La 1.12 x 10^11 yes

147Sm 1.06 x 10^11 yes

87Rb 4.88 x 10^10 yes

187Re 4.3 x 10^10 yes

176Lu 3.5 x 10^10 yes

232Th 1.40 x 10^10 yes

238U 4.47 x 10^9 yes

40K 1.25 x 10^9 yes

235U 7.04 x 10^8 yes

244Pu 8.2 x 10^7 yes

146Sm 7.0 x 10^7 no

205Pb 3.0 x 10^7 no

247Cm 1.6 x 10^7 no

182Hf 9 x 10^6 no

107Pd 7 x 10^6 no

135Cs 3.0 x 10^6 no

97Tc 2.6 x 10^6 no

150Gd 2.1 x 10^6 no

93Zr 1.5 x 10^6 no

98Tc 1.5 x 10^6 no

154Dy 1.0 x 10^6 no

As seen above, every nuclide with a half-life less than 80 million years (8.0 x 107) is missing from our region of the solar system, and every nuclide with a half-life greater than 80 million years is present. That means the solar system is much older than 80 million years, since the shorter-lived nuclides have simply decayed themselves out of existence. Since a nuclide becomes undetectable after about 10 to 20 half-lives (Dalrymple, page 378), multiplying 80 million times 10 (or 20) gives us about 800 million years (or 1.6 billion years). The earth must be at least that old since these nuclides have disappeared from nature.

R. Sungenis: Not provable. The only thing we can safely say that the above numbers tell us is the half-life of the nuclides is in the 10^15 to 10^6 range and that some appear in our solar system and some do not. From a Creationist standpoint, God simply made the elements and designed them with the half lives we still see today. Some He included in our vicinity, some He didn’t. The only thing we CAN say based on the half lives is that, if the Earth were to last 10^15 billion years, than half of the present Hafnium, for example, would still be present in 10^15 billion years. Any other conclusions are just speculation.

Porvaznik: For a more precise age of the earth, the technique of radiometric dating has been successfully used since the 1950s (i.e. C.C. Patterson of the California Institute of Technology in 1953 is considered the first scientist to calculate the true age of the earth at c. 4.5 billion years).

Radiometric Dating Methods

The ages of meteorites and rocks from the earth and moon are measured by radiometric dating, a family of techniques based on the spontaneous decay of long-lived naturally occurring radioactive isotopes. These radioactive parent isotopes decay to stable daughter isotopes at rates that can be measured experimentally and remain effectively constant over time regardless of physical or chemical conditions. Each parent-daughter pair constitutes an independent clock in which atoms of the parent are transformed at a constant and predictable rate into atoms of its daughter. The amounts of parent and daughter isotopes in a rock, along with the known rate of decay, provides the information necessary to determine the time that has elapsed since the rock formed (Dalrymple, page 79).

Here is a table of the parent-daughter isotopes, their calculated half-life, and their known decay constants used to determine the ages of rocks and minerals.

Principle Parent and Daughter Isotopes

Used to Determine the Ages of Rocks and Minerals

[ From G. Brent Dalrymple (page 80) ]

Parent Isotope Daughter Isotope Half-Life

(millions of years) Decay Constant

40K 40Ar 1,250 5.81 x 10^-11

87Rb 87Sr 48,800 1.42 x 10^-11

147Sm 143Nd 106,000 6.54 x 10^-12

176Lu 176Hf 35,900 1.93 x 10^-11

187Re 187Os 43,000 1.612 x 10^-11

232Th 208Pb 14,000 4.948 x 10^-11

235U 207Pb 704 9.8485 x 10^-10

238U 206Pb 4,470 1.55125 x 10^-10

Of the 339 isotopes of 84 elements found in nature, 269 are stable and 70 are radioactive. Eighteen of the radioactive isotopes have long half-lives and have survived since the elements of the solar system were created. These long-lived radioactive nuclides are the basis for radiometric dating (Dalrymple, page 80).

The basic formulas used to calculate the ages are (warning, a little algebra and a logarithm here):

Pt = P0 e-dt

P0 = number of parent atoms at some starting time

Pt = number of parent atoms at some later time t

d = the decay constant (above)

Since P0 = Pt + Dt

and Dt = the daughter atoms formed

Substituting Pt + Dt for P0 we get

Pt = ( Pt + Dt ) e-dt

Now solving for t we get

t = ( 1 / d ) loge ( Dt / Pt + 1 )

which is the basic radiometric-age equation and contains only quantities that can be measured today in the laboratory. If the rock incorporated some of the daughter isotope when it formed, then this initial amount of the daughter must be subtracted from the total amount measured. However, for the principal methods, the value of the initial daughter is either zero, negligible or not required (Dalrymple, page 84-86).

A Catholic creationist in an Email to me states:

<< In the first place, radiometric dating is based upon pure assumption and speculation. The scientist must assume he knows the ratio between potassium and argon that existed in the beginning. But, how can he know this? He must supply the original ratio based upon a supposition rooted in uniformitarian philosophy. It is the same for carbon14 dating. >>

This is a convenient dismissmal of the science of radiometric dating (no doubt picked up from some young-earth creationist literature). Radiometric dating is not "based upon pure assumption and speculation." And Carbon-14 dating is not used to date the oldest rocks (the half-life of 14C is about 5,700 years and can be used to date objects up to around 50,000 years old). There are several types of radiometric dating methods with various accumulation clocks that are self-checking (especially with "isochron" or "concordia-discordia" methods) when used to measure multiple samples of the same rock or minerals. These methods are the K-Ar (Potassium-Argon) Method, the Rb-Sr (Rubidium-Strontium) Method, the Sm-Nd (Samarium-Neodymium) Method, the Lu-Hf (Lutetium-Hafnium) Method, the Re-Os (Rhenium-Osmium) Method, and the U-Th-Pb (Uranium-Thorium-Lead) Methods.

On the reliability of these methods, see the detailed TalkOrigins articles Isochron Dating FAQ and Radiometric Dating and the Geological Time Scale

K-Ar (Potassium-Argon) Method

This method is based on the decay of 40K to 40Ar and is probably the most commonly used radiometric dating technique available to geologists. It is the only decay scheme that can be used with little or no concern for the initial presence of the daughter isotope. This is because 40Ar is an inert gas that does not combine chemically with any other element and so escapes easily from rocks when they are heated.

Like all radiometric methods, the K-Ar method does not work on all rocks and minerals under all geologic conditions. It works particularly well on igneous rocks that have not been heated significantly since their formation. It does not work on most sedimentary rocks because these rocks are composed of debris from older rocks. It also does not work on many metamorphic rocks because rocks of this type formed from other rocks under heat and pressure. The K-Ar method is of limited use for the dating of meteorites, lunar rocks, or the oldest rocks from the earth due to its susceptibility to resetting by later heating. The 40Ar / 39Ar variant of the method overcomes many of these problems (Dalrymple, page 90-94).

R. Sungenis: Potassium 40 breaks down into 88.8% Calcium 40 and 11.2% Argon 40. Although one could date rocks by calculating the Calcium 40 method, scientists realize that they do not know how much Calcium 40 was originally present. Instead, they date according to Argon 40, assuming that, when igneous rock melts and then hardens, the Potassium 40 decay to Argon 40 begins again. But the problem with this is that: (1) there is no way to know that all of the Argon 40 escaped when the rock melted; (2) there is always an amount of air-Argon remaining in the rock when it hardens, especially since air contains 1% Argon. Knowing these anomalies in the Potassium-Argon method, scientists tried to solve the problem by the Argon-Argon method. This method subjects the rock against a nuclear reactor for several hours. The nuclear reactor emits a large number of neutrons, which stimulates Potassium 39 to decay into Argon 39. The rock is then heated to release both Argon 40 and Argon 39 (representing the Potassium). The ratio of these are measured to determine the amount of Potassium 40 originally present. But the problem with this method is that if the rock has experienced high temperatures during any part of its formation, this will give a null result to the dating. As it stands, Potassium-Argon and Argon-Argon are thought to be the best dating methods, since it is believed that one can determine the original amount of daughter element in the sample, but as we have seen, the anomalies remain.

Porvaznik: Rb-Sr (Rubidium-Strontium) Method

The Rb-Sr method is based on the radioactivity of 87Rb which undergoes decay to 87Sr with a half-life of 48.8 billion years. Rubidium occurs as a trace element in most rocks. Strontium is present as a trace element in most minerals when they form (unlike Argon, which escapes easily and entirely from most molten rocks). The Rb-Sr dating is done primarily with the "isochron method" which completely eliminates the problem of initial Strontium. Because of the long half-life of 87Rb, the Rb-Sr dating is used mostly on rocks older than about 50 to 100 million years, for only in these rocks has sufficient time elapsed for measurable quantities of 87Sr to accumulate. Because of its relative resistance to post-formation events, the Rb-Sr dating (by the isochron method) is used extensively to determine the ages of the oldest rocks in the solar system (Dalrymple, page 94-95).

Sm-Nd, Lu-Hf, and Re-Os Methods

In recent years the Sm-Nd (Samarium-Neodymium) method has appeared in the geological literature, and has become a common tool for geochronologic studies of old rocks and meteorites. The Sm-Nd method is more resistant to metamorphism than are other dating methods which gives it a decided advantage for age measurements of very old rocks. Ancient basalt and the achondrite meteorites contain so little K, Rb, and U that precise dating can only be done with the Sm-Nd method. The Lu-Hf (Lutetium-Hafnium) and Re-Os (Rhenium-Osmium) methods while infrequently used, provide some valuable data relevant to the age of meteorites (Dalrymple, page 95-97).

R. Sungenis: All the other dating methods, e.g., Rubidium-Strontium; Samarium-Neodymium; Lutetium-Hafnium, etc, are all less accurate since, by their own admission, scientists realize that there is always some undetermined amount of the daughter element in the original sample.

Porvaznik: U-Th-Pb Methods

These methods are based on the radioactivity of 235U, 238U, and 232Th which all decay to different isotopes of Pb (Lead). Although these involve a decay series with intermediate radioactive daughter products, the decays of 238U to 206Pb, 235U to 207Pb, and 232Th to 208Pb can be treated as a simple one-step decay since each of the three series are entirely independent of the others and the half-lives of the intermediates are very much shorter than the three parents. Because of the problems of initial Pb and Pb loss the U-Th-Pb methods of dating are most often applied with the use of "isochron" or "concordia-discordia" diagrams which circumvent the initial daughter problems mentioned earlier (Dalrymple, page 99-102).

R. Sungenis: One of the more popular radioactive methods is the measurement of the decay of Uranium into Lead. Evolutionary theory holds that the half-life of Uranium 238 is 4.5 billion years, which, since they estimate the earth to be the same age, serves as a coincidental dating device. Other elemental pairs used in radiometric dating are: Samarium 147 to Deodymium 143 (half-life of 106 billion years); Rubidium 87 to Strontium 87 (half-life of 48.8 billion years); Rhenium 187 to Osmium 187 (half-life of 42 billion years); Lutetium 176 to Hafnium 176 (half-life of 38 billion years); Thorium 232 to Lead 208 (half-life of 14 billion years); Potassium 40 to Argon 40 (half-life of 1.26 billion years); Uranium 235 to Lead 207 (half-life of .7 billion years); Beryllium 10 to Boron 10 (half-life of 1.52 million years); Chlorine 36 to Argon 36 (half-life of 300,000 years); Carbon 14 to Nitrogen 14 (half-life of 5715 years). Data taken from N. E. Holden’s Pure Appl. Chem. 62 (1990): 941-958. Whether these decay rates are correct or not remains to be seen. Decay rates measured within the last 50-80 years depend on a pure parent sample which is set aside for a length of time to produce the daughter element, but this assumes that the present decay rate has always been the same, which cannot be proven.

Taking the known decay rate of Uranium from laboratory experiments, these results can then be compared to the remaining Uranium in the rock specimen, along with the amount of Lead in the rock, and it can be estimated how long it has taken for the Lead to form from the original Uranium. Although this sounds quite logical, it is only so in theory. The reason is that such a method depends on three unprovable assumptions:

(1) all the Lead found in the specimen must be assumed to be originally from Uranium, but there is no way to know this for certain. There may have been some Lead already in the rock when it was formed, before the Uranium in the rock began to decay. Since it is known that natural Lead appears in rock, it is quite presumptuous to attribute all of it to Uranium decay. Of course, if the amount of Lead in the rock pre-existed the decay of Uranium, then the age of the rock will turn out to be much less than if all the Lead in the rock was due to Uranium decay.

(2) Due to the process of leaching, Uranium, as well as other radioactive elements, are quite capable of dissolving in water. Hence, if the rock was subjected to water for any length of time (of which there is an abundant supply on earth), this would directly effect the amount of Uranium the rock would contain at any given time. In this scenario, if one were to measure the age of the rock unaware that Uranium had leached out, the estimation of age would be much too great. Biblical scientists, who hold to a world-wide deluge as recorded in Genesis 6-9, assert that these flood waters would disrupt all such isotope dating in which the parent element was subject to leaching.

(3) Current radiometric dating assumes the rate of decay has remained constant for millions of years, without any appreciable deviation due to outside forces. This is commonly known as uniformitarianism. Although it is true that radioactive atoms have been subjected to temperature, pressure and chemical changes in the laboratory without changing their decay rate, still, natural forces, such as neutrinos from cosmic radiation disturb the decay process. The decay rates of ions are known to differ from neutral atoms. Decay rate is also based on the speed of light, which, as of this past decade, numerous laboratory experiments and astronomical anomalies show that it is not constant. In addition, such things as the reversal of the earth’s magnetic field, which has been documented as occurring in both the past and near present, as well as any galactic event, such as a supernovae explosion, could cause alterations to the decay rate of radioactive elements.

Although other elements are often used to measure radioactive decay, such as Potassium, Thorium, Strontium, and a half dozen others, they are all subject to the same above caveats as Uranium. In fact, some of these elements are even more soluble in water than Uranium salts.

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