Most people accept the current old-earth (OE) age estimate of around 4.6 billion years. This age is obtained from radiometric dating and is assumed by evolutionists to provide a sufficiently long time-frame for Darwinian evolution. And some OE Christians see no problem with this dating whilst still accepting biblical creation, see Radiometric Dating - A Christian Perspective. This is the crucial point. It is claimed by some that an old earth supports evolutionary theory and by implication removes the need for biblical creation. Some claim Genesis in particular, and the Bible in general looks mythical from this standpoint.
A full discussion of the topic must therefore include the current scientific challenge to the OE concept. This challenge is mainly headed by Creationalism which teaches a young-earth (YE) theory. A young earth is considered to be typically just 6,000 years old since this fits the creation account and some dating deductions from Genesis. Moreover, if YE theory can be established scientifically, then macroevolutionary theory falls. It may of course turn out that YE theory goes the same way as the 'flat-earth' theory of the middle ages, but it needs to be examined.
Accepted Dating Methods
Here we outline some dating methods, both absolute and relative, that are widely accepted and used by the scientific community. Absolute dating supplies a numerical date whilst relative dating places events in time-sequence; both are scientifically useful.
This is based upon the spontaneuous breakdown or decay of atomic nuclei. Radioactive parent (P) atoms decay to stable daughter (D) atoms e.g. the carbon isotope C-14 decays to nitrogen-14 and the uranium isotope U-235 decays to the lead isotope Pb-207. The time required for half the original number of parent atoms to decay is called the half life. Some half-lives are listed below:
It follows that uranium-lead, potassium-argon (K-Ar), and Rubidium-Strontium (Rb-Sr) decay can be used for very long time periods, whilst radiocarbon dating can only be used up to about 70,000 years. The K-Ar method is often used for rock dating. This uses a simple exponential decay formula linking the original number, Po, of parent atoms in rocks and minerals to the P atoms now present, thereby enabling an estimate of geological age. Mathematically, P = Po exp(-lambda T), where lambda = the decay constant and T = the period of decay. Assuming Po = P + D i.e. a zero initial number of D atoms, where P(or D) = the current number of P(or D) atoms, it follows that the age of a rock or mineral is computed as T=(1/lambda)ln(1 + D/P). Using radiometric techniques, the oldest dated minerals (4.0 - 4.2 billion years) are zircon crystals found in sedimentary rocks in western Australia.
One problem with earth dating is that the original earth surface is assumed to have eroded long ago. But assuming the earth was formed at the time of the rest of our solar system, then recovered moon rock and meteorites can also be used to estimate the age of the earth. These estimates give 4.4-4.5 billion years for moon rock, and 4.54 billion years for iron metreorites.
These techniques utilize the physical parameters of the earth, such as ice cores, annual lake sediments, and astronomical cycles.
Ice cores from Greenland and Antarctica show annual layers (varves) and can be traced up to about 40,000 years before the layers become too thin due to compaction. Similarly, annual lake sediments can be used to estimate relative age and conventional interpretation for the Green River varves suggests they have been formed over some 20 million years. This implies the earth is at least 20 million years old.
Astronomical cycles can also be used to measure relative age. The earth precesses (wobbles like a spinning top) around the sun in a series of cycles. These cycles affect sunlight and hence long-term can form layers in rock. In some cases these astronomical cycles in rock appear to have been laid down over some 25 million years (and radiometric dating puts the absolute age of the rock at some 200 million years).
Disputed Dating Methods
Here we outline dating methods that are disputed in the scientific community. Invariably they give the age of the earth to be very much less than that found by radiometric dating.
One early approach was based upon ocean salinity [John Joly, 1800's]. This assumed the ocean was initially pure water and that it's salinity was derived from continental erosion. The technique gave 90 million years, but took no account of the non-constant erosion rate, or the loss and recycling of salt, or the fact that salt is obtained from other sources as well as continents. More recently, work has been done on ocean sediments [S. Nevins, Institute for Creation Research]. This suggests that, given the current annual rates of erosion (some 27.5 billion tons), all earth's continents would be delivered into the oceans in just 14 million years. Clearly, this seems incompatible with an ocean billions of years old. However, this may be a simplistic computation since there is Sediment Recycling as sediments accumulate and cause continental plates to collide, resulting in land uplift and subsequent errosion.
Another dating method is based upon the decay of the earth's magnetic field [T.G. Barnes, 1973] [The Creation of Planetary Magnetic Fields, D. R. Humphreys, 1984]. Barnes and Humphreys maintain that the earth's currents and fields would decay steadily over thousands of years, and that the present magnetic field strengths of the Earth, Sun, Moon, and planets agree very well with the values produced by their theory and a 6000-year age for the solar system.
Scientists agree that the earth's magnetic field is weakening and they have observed a 10% decline in the magnetic dipole over the 20th century. At the current rate of decline it could take just 1,500 years to disappear, with increasing effects upon the electronic systems of satellites and spacecraft. This time-scale seems reasonable given the Barnes/Humphreys model. Conversely, with a half-life of 1,400 years, the magnetic field would be 32 times the current value just 7,000 years ago! But to counter this, the rigour of the Barnes/Humphreys theory is disputed, see talkorigins.
The decay of uranium and thorium isotopes results in a net build-up of Helium-4 atoms in the atmosphere. It is claimed to be increasing at an annual rate of 3.5 x 10^11 grams, and that there are some 3.5 x 10^15 grams of Helium-4 currently in the atmosphere [Nuclear Geology, H. Faul][Nature 179,213, M. Cook]. From these figures and known decay rates, it can be shown that the current amount of atmospheric Helium can be generated in just 11,000 years (not billions of years). The use of this approach to measure absolute geological age has been controversial for over 100 years and the YE it suggests has been attributed to Helium loss (see U-Th/He thermochronometry). On the other hand, some claim recent research supports a Helium Diffusion Age of 6,000 ± 2,000 years.
Short-period comets orbit the sun in less than 200 years (the Halley comet orbits about every 76 years). Each time they come close to the sun they lose material (the comet tail) and disintegrate. If no new comets are being generated, it would appear that no short-period comets can survive more than about 10,000 years - implying a young earth. This claim is countered by the fact that the origin of short-period comets is still uncertain and that there may be a source of short-period comets e.g. the Kuiper Belt Objects (KBOs) in the Uranus-Neptune zone, or the Oort Cloud.
Scientific Debate
Earth dating via ocean sediments, magnetic field decay, atmospheric helium, short-period comets (and other techniques) point to a young earth. However, the scientifc accuracy of YE claims are frequently challenged e.g. Evidences for a Young Earth? and Talk Origins. In order to balance the discussion we should also challenge the currently accepted radiometric dating methods. If these are suspect then the disputed methods take on more meaning.
Most rock dating methods rely on the following basic assumptions:
There are several causes for concern here. The K-Ar method dates rocks by measuring the accumulated Ar-40. It is claimed the advantage of this method is that it circumvents the zero date problem i.e. there is little concern for the initial presence of the daughter isotope, Ar-40, since it is assumed that the inert gas escaped as the rock solidified. In other words, all Ar-40 in a rock is assumed to have been produced by in-situ radioactive decay of K-40 within the rock since it formed and there was zero Ar-40 in the rock when it solidified. However, this primary assumption has been challenged e.g. in Radiometric Dating Methods, Pitman, 2004 and in Radio Isotopes and the Age of the Earth, Vardiman et al. This 'zero Ar-40' problem has also been identified by Snelling who comments for one research project:
"Available evidence indicates the excessively old 'ages' are due to excess Ar-40 in the basalt which was not derived from in- situ decay of parent K-40 but inherited by the lava from its source."
Furthermore, since the Ar gas is not chemically bound to other atoms, it may leak in or out of samples and violate the assumption of no leaching/addition (see Radio Isotopes and the Age of the Earth). Certainly it is known to diffuse easily from deeper rocks under pressure so surface rocks tend to have a higher Ar-40 concentration than would be expected. This, coupled with the fact that potassium is easily washed out of minerals, suggests this technique can give an artificially high age for the earth and leads some to conclude that:
"... all K-Ar and Ar-Ar 'dates' of crustal rocks are questionable ..." [D. Pitman, Radiometric Dating Methods, 2004]
If we question these techniques, there is an alternative method called isochron dating. The isochron dating method attempts to combat the zero date problem by using ratios of isotopes and samples of different minerals from the same rock. For example, a plot of Sr-87/Sr-86 against Rb-87/Sr-86 for different minerals yields a straight line, and the slope of the line is simply (lambda)T where T is the age estimate. However, it still relies on certain basic assumptions, and in particular on the assumption that the specimen was entirely homogenous when it formed i.e. not layered or incompletely mixed. This is questionable for many isochron-derived dates, see Radiometric Dating Methods and Radio Isotopes and the Age of the Earth. The method also assumes that all mineral samples will have the same initial Sr-87 to Sr-86 ratio, but this is not always the case. So whilst isochron dating can give a straight line, the slope may have no significance [Vardiman et al].
What about the radiometric assumption of constant decay rate? Such an assumption rests on the old evolutionary concept of uniformitarianism. In broad terms this means the observed geological features are the result of slow geological forces of the same kind and intensity as those found today. And for radiometric dating it means that the decay constant of the parent has not changed over earth's history. Scientific justification for this assumption is found for example in Radiogenic Isotope Geology, A. P. Dickin. The overall theme is that of a very old earth.
In contrast, Humphreys has proposed an accelerated decay (higher decay rate) early in earth's history, leading to a younger earth. This idea has been rebutted by those who claim there is no known scientific mechanism to produce such a change, see for example Claims of Accelerated Radioactive Decay and Tim-Thompson: decay rate. Others disagree and say that studies in theoretical physics suggest accelerated nuclear decay can occur e.g.:
Uniformitarianism is also challenged if we invoke the concept of a world-wide flood (for which there is much evidence). Vardiman et al claim that this would result in unreliable radioisotopic dating. Vardiman et al conclude from their research that:
"Conventional radioisotopic dating methods are unreliable. The chief reason is that uniformitarianism is not a legitimate model of earth history. Observational evidence supports the recent occurrence of a global catastrophic flood."
Two Views on Creationalism
As stated above, some OE Christians see no problem with radiometric dating and readily accept OE theory whilst still accepting the biblical concept of creation, see for example Radiometric Dating - A Christian Perspective. In fact, there are many Notable Old Earth Christians and quotes from a few are given below:
"As for the age of the earth and the universe, within the usual limits of any scientific conclusions, I believe that the present calculations of about 4 billion years for the earth and 14 billion years for the universe are not far wrong, and I see no conflict with that understanding and my understanding of the Bible." [W. D. Phillips, a Christian and Nobel Prize winner for Physics in 1997]
"I believe that radioactive dating methods may not be as accurate as many people claim, but nevertheless I believe they are sufficiently accurate to show that our earth really is very old." [C. Humphreys, physicist and Professor of Materials Science, University of Cambridge]
"Three independent techniques date the universe at approximately 10 to 15 billion years. Is this a problem with respect to the Bible as some Christians seem to feel it may be? The answer to that is certainly 'No.'" [R. Gange, PhD, research scientist and professional engineer]
"As a Christian, I am a theist and believe that God created the world. I do not regard Genesis as a scientific text. I have no vested theological interest in the age of the earth or the universe. I find the arguments of geologists persuasive when they argue for an earth that is 4.5 billion years old." [W. A. Dembski, PhD, Research Professor in Philosophy]
"Four billion years ago, the conditions on this planet were completely inhospitable to life as we know it; 3.85 billion years ago, life was teeming. That is a very short period —150 million years— for the assembly of macromolecules into a self-replicating form. I think even the most bold and optimistic proposals for the origin of life fall well short of achieving any real probability for that kind of event having occurred. Is this where God entered? Is this how life got started? I think it is noteworthy that this particular area of evolution, the earliest step, is still very much in disarray." [F. S. Collins, PhD, Director of the National Human Genome Research Institute at NIH]
Some Christians who adopt this worldview will have examined maintstream scientific dating but still doubt the OE theory. They may accept that the current scientific argument against a YE seems to be winning and that YE science seems relatively weak. Also, non-radiometric dating techniques using ice cores or astronomical cycles give relative ages of typically 20 million years, which are difficult to dispute. The earth seems to be at least 20 million years old even if all radiometric dating is incorrect! But there are several factors that may still worry them:
BIBLICAL EARTH CHANGES:
The Bible records two dramatic, worldwide physical changes to the earth:
At the Fall of man the whole of creation, including the earth, was suddenly subjected to corruption or decay (Rom 8.20-22). The ground itself was 'cursed' resulting in cultivation problems (Gen 3.17,18). Also, at the Flood there were catastrophic geological changes, see for example geological evidence for the flood and scientific evidence. Some see these physical events having a sudden effect upon physical laws e.g. the introduction of the Second law of Thermodynamics, which essentially states that open or closed systems tend to deteriorate with time i.e. entropy increases [Creation Scientists Answer their Critics, D.T. Gish]. In short, the earth's order is deteriorating with time. This concept may be supported by theoretical physics, which suggests that a decrease in the speed of light together with an evolution (change) of some physical constants with time is a possible cosmoligical model of the universe, see Physical Constants and the Evolution of the Universe, Troitskii, 1987. Physical changes are also suggested from the biblical accounts of man living to over 900 years prior to the flood (Gen 5).
Could these biblical events and the associated physical changes have caused accelerated radiometric decay, and by implication destroy uniformitarianism, the bedrock of radiometric dating? These biblically-implied abrupt physical changes in the earth are largely ignored in radiometric dating, which may be the source of the OE and YE discrepancy.
BIBLICAL THEOLOGY OF SIN:
A literal interpretation of Genesis suggests that all living land creatures, including man, were created as herbivores rather than carnivores (Gen 1.29,30). The concept of killing for food is absent from the early Adamic world of the Bible. This conflicts with the evolutionary model, but is in accord with other scriptures. In particular, death only entered the world through Adam's sin (Gen 1.17)(Rom 5.12) and so could not have existed prior to this. Theologically therefore, it is difficult to conceive of millions of years of man's evolution prior to Adam since this implies such creatures never died! The world would be heavily populated by both animals and man by the time Adam came along! This may be a problem for OE creationalists if they hold to the doctrine of Adam's sin being the origin of death. And those who cannot accept a literal Adam will have to explain away the detailed genealogies of Gen 5 and Lk 3, which trace Adam's descendants. Adam is dated c4000 BC (Ussher, 1664), making a young earth about 6,000 years old!
Conclusion
For many Christians the jury is still out. Scientifically it seems the OE theory is very well supported, although there are serious descenting scientific voices. Theologically it seems difficult to accept OE creationalism and dismiss YE creationalism when the Bible is read literally. The basic question seems to be "where is one's starting point?". For all Christians the bottom line should be:
'In the beginning God created the heavens and the earth' (Gen 1.1)
Bible quotations are from the New American Standard Bible
Related topics: Evolution ; What is Truth? ; Reality