As a former geology instructor, I occasionally had students who, for religious reasons, objected to the discovery by science that the Earth and the universe are incredibly ancient. Personal beliefs are none of my business, and I didn't want to get caught up in religious-based disputes. However, because the science is well-established, and because I was educating future science teachers, I felt a responsibility to do my best to insure that science teachers finishing my courses go into the classroom teaching science and not religion posing as science. To this end I felt the need to respond to a pamphlet I received anonymously when I was a professor, authored by D. Russell Humphreys, Ph.D., that contains arguments that the Earth is young (that is, just a few thousand years old – 6000 years is often quoted).
There are reasonable explanations to all his arguments. In the interests of the vast majority of my students, since I did not think it appropriate to spend excessive amounts of class time addressing controversies that have long been settled scientifically, I wrote a response to each of Humphreys' arguments and posted them on my college website (no longer present) for students to access, if interested. I've decided now to post an updated version on my current website in the hope that, if anyone has questions concerning these arguments (which may well sound convincing to those without the proper scientific background), they can find that they are without scientific merit.
Humphreys resurrects an old astronomical paradox involving spiral galaxies. These galaxies rotate more rapidly near the center than farther out. Given enough time the spiral arms should wrap themselves up so tightly they would disappear. He notes the current explanation - density waves - but writes that a study of the Whirlpool Galaxy ["Inner spiral structure of the galaxy M51", by Dennis Zaritsky et al, Nature 364, 313-315 (22 July 1993)] has "called into serious question" the density-wave theory.
Density waves are waves that propagate through the gas and dust of interstellar space by means of gravitational interaction between the particles of gas and dust, similar in some ways to the propagation of sound waves through a gas by means of pressure interactions. That such a wave could exist is based on well-established physics, so the only questions are, "Do they occur?" and "Are they the cause of spiral structure?"
The answer to the first question is a definite "yes". Density waves have been detected in Saturn's rings by both the Voyager and Cassini spacecrafts. Cassini monitored the behavior of these waves, which have a profound effect on the ring structure, during its mission at Saturn. There are matter density and scale differences, of course, between Saturn's rings and spiral galaxies; however, the same types of computer simulations are applied to both and when applied to galaxies suggest these waves do occur and do lead to spiral structure. In fact, the density-wave theory of galaxies led to the prediction of waves in the rings of Saturn before they were actually observed.
The observational evidence for these waves in galaxies includes the birth of hot, young stars as these waves pass through the interstellar dust and gas medium, indicating compression of this medium by the waves. These stars mark the extent of the arms in visual images of spiral galaxies. However, what about the problem of M51, the Whirlpool Galaxy?
Humphreys implies that the authors of the Nature report referenced above have called the density-wave theory into "serious question". Using infrared wavelengths, they traced the spiral arms much closer to the center of the galaxy than previously thought possible. This does not overthrow the concept of density waves but requires an expanded theory of spiral formation. Zaritsky et al suggest a combination of factors might produce the observed structure, including the effect of density waves. Humphreys comes close to misrepresenting the work of these authors in his pamphlet.
If galaxies are only a few thousand years old, then people like Humphreys have a lot more explaining to do than scientists. For starters, how come you can even see the Whirlpool Galaxy? Even if you reject scientific yardsticks of measurement, look at how small it appears in the sky versus how large it would have to be to contain all those stars. Certainly, it must be somewhere in the vicinity of its estimated 31 million light years distance. Shouldn't the light have 31 million minus, say, 6000 years of travel time ahead of it before it reaches our eyes? How is it we can observe it?
Finally, it is interesting to note his argument could just as well be used to "prove" a hurricane can't last for the week or so it may take it to travel from off the west coast of Africa to the western Atlantic. After all, meterologists still don't understand exactly how hurricanes work and how the convective spiral arms form. As in the case of spiral galaxies, hurricanes "rotate" faster near their centers. Therefore, these arms should wrap themselves up, and the hurricane should fill in and vanish. Rest easy Florida!
Humphreys makes several misstatments in this argument. He maintains that comets don't last very long, geologically speaking, which is true, but refers to the "improbable" gravitational interactions that could cause new comets to enter the inner solar system from the "unobserved" Oort cloud, or lead to the capture of the comets into inner solar system orbits.
Where has this guy been? Where was he when Hale-Bopp appeared? Where was he when the orbit of comet Shoemaker-Levy 9 was perturbed by Jupiter to the point it crashed into that planet?
Ever since the day of Edmund Halley, astronomers have been calculating the orbits of comets using Newton's law of gravitation. The Oort cloud is of course unobserved because it consists of these relatively small (up to a few kilometers in size) objects that orbit the Sun up to a third of the way to the nearest star. However, the Oort cloud is known to exist because that's where many new comets come from as calculated from orbital dynamics. This is the same orbital dynamics that guides spacecraft to their destinations (unerringly, unless you confuse feet with meters as in one failed Mars mission).
Enough comets have come from the Oort cloud into the inner solar system that the extent, size, and comet population of the cloud can be known fairly well. So the "improbable" interactions claim is baloney. Comets do come into the inner solar system from a distant region surrounding the Sun. His statement, "So far, none of these assumptions has been substantiated, either by observations or realistic calculations." implies either ignorance or deliberate deception.
Similarly, orbital dynamics (more of those "unrealistic" calculations), nicely accounts for the orbits of the comets now plying the inner solar system if there has been ample time for the incoming comets to interact gravitationally with the giant planets (primarily Jupiter). However, these comets come primarily from another source of comets, the Kuiper Belt. Unlike the Oort Cloud, objects of the Kuiper Belt have been observed. Of course, if the solar system is only a few thousand years old, there would not be time for these comets to accumulate. The fact they are there is evidence for, not against, an ancient solar system.
In this argument, Humphreys claims there is only about, on average, 400 meters of sediment on the ocean floor, including that on the continental shelves. At the current rate of supply by erosion, he says, even taking the removal of sediment by subduction into account, that is much too small an amount to account for billions of years of Earth history. ("Subduction" is the process where oceanic crust that was originally formed at ocean spreading centers returns into the Earth as part of a gigantic convection "conveyor belt" that brings new material to the surface and takes old material back into the Earth.)
First of all, he really low-ball's the estimated average depth of sediment, which is closer to 1500 meters, almost four times the number he provides. Then, if you make a reasonable estimate of the amount of sediment lost per year by subduction (around 5 × 108 cubic meters per year), it would take "on the order of" one billion years to remove that sediment. (This estimate uses a subduction rate of 1 centimeter per year, the average thickness given above, and a total subduction zone length on the order of the Earth's circumference. The expression "on the order of" means roughly approximate to a power of ten.)
To check these figures, you can estimate the average erosion rate of the continents per year by dividing the subducted sediment by the area of the continents. That caculation gives you an average erosion rate of about 0.004 millimeter per year, which is close to the accepted value of about 0.005 millimeter per year. Remember, these are very approximate calculations, but they show that there is no basis for his argument.
Even if more sediment is entering the ocean currently than is being destroyed by subduction, all this means is that either erosion rates will slow as the land is worn down, restoring the balance until mountain-building is accelerated, or else the large amounts of sediment entering the oceans will result in an eventual increase in the rate of sediment destruction at subduction zones. (Both mechanisms are likely.)
The "not enough mud" argument is quite silly when you think about it. It is like arguing a car is only a few hours old because more gas is leaving the tank than entering it (zero for most cars I'm aware of) as you drive. Since the tank only holds so much gas, the car can't be any older than what the rate of gasoline use would indicate, right?. You would shake your head at this moronic conclusion and simply fill up at the next gas station.
Humphreys says that more sodium is entering the sea than is being removed, and that the calculations most favorable to evolution still require the Earth to be no more than 62 million years old. Well, I'll have to defer to the chemists on this one. A good place to start for the answer to this apparent paradox is found at the talkorigins website. As a geologist of sorts, I happen to know of huge amounts of salt (sodium chloride) locked up in sediments such as those at the bottom of the Gulf of Mexico and the Mediterranean, and in continental basins such as the Michigan Basin. In addition, the chemists say the creationists greatly underestimate the sodium used in the alteration of oceanic basalts. This is no surprise to me, since they refuse to admit the well-established process of seafloor spreading, which continuously produces huge amounts of basalt at ocean spreading centers. At any rate, the same considerations apply here as in the case of the "not enough mud" argument. An imbalance now, even if it exists, does not imply an imbalance throughout geologic time.
However, salt and other dissolved substances in the ocean are, to my mind, more a problem for the creationists than the scientists. Incredibly, they admit that, at today's rates of input, it would take 40 million years to make the ocean as salty as it is today. I didn't get into physics because I couldn't do math: 40 million years is way longer than 6000 years. According to the reference cited above, calculations indicate a balance between sodium input to ocean water and sodium removal, so there doesn't appear to be a real problem here anyway.
Humphreys dismisses modern magnetohydrodynamic (MHD) theory that explains the existence of solar, stellar, and planetary magnetic fields as "very complex and inadequate". Well, he is half right. MHD equations are very complex, being highly "nonlinear" – a mathematical term meaning "you need a computer to solve them". MHD equations are based on sound physics. It's just that they are a bear to solve. This has made progress slow in truly understanding the nature of the generation of the Earth's magnetic field in its molten iron core. (Not to mention that the core is out of sight thousands of miles underground.)
Nevertheless, it is clear from electromagnetic theory that electric currents coupled with convection in the molten iron core (MHD) can certainly generate the Earth's field. Just because a theory is mathematically difficult doesn't mean it's wrong. (The most accurate theory in physics, quantum electrodynamics, is also extremely complex.) And MHD is definitely not inadequate. (The computers are.)
So, basically, Humphreys can't really trash the idea of an ancient Earth by saying, "Gosh, MHD is so dang hard – there must be another explanation." But, he tries anyway, and, not surprisingly, his explanation jibes with a young Earth. His paleogeomagnetic theory (aka "history of the Earth's magnetic field") has the field created without any sustaining energy, so it has to gradually "decay" (diminish over time).
The only solid evidence he has, as far as I can see, is that the Earth's field has indeed weakened over the last several thousand years as indicated by "fossil magnetism". However, fossil magnetism also shows the field has increased and decreased and even reversed itself (north and south magnetic poles switching) over geologic time, so my first thought is, "So it's been decreasing lately, so what." Of course, Humphreys rejects geologic time.
Another aspect of Humphreys' theory are the presumed rapid fluctuations and reversals of the magnetic field, beginning with the flood of Noah and lasting for a few thousand years after that. Others have examined Humphreys' supposed evidence for these rapid reversals and come away with a response best characterized as, "Huh?". The short story is there is no such evidence. It's amazing how creationists will reject sound, scientifically well-established evidence while, at the same time, shoring up their arguments with the most flimsily manufactured, unsubstantiated "evidence".
Humphreys doesn't explain what "too tight" is. According to the science of rheology (the study of the deformation of solids), there is no "too tight", given large stresses acting at elevated temperatures over long periods of time. In particular, he claims the fact sedimentary beds are sometimes tightly folded proves they could not have been solid rock at the time they were deformed. Thus, according to him, they had to have been folded in a short time before they solidified.
Well, if you have the time and money, you might take a trip to the snout of a large glacier and observe the tightly folded ice exposed by melting. Would Humphreys argue that that proves the folding occurred while the glacier was liquid? (How would you fold liquid water, exactly?) Just as ice deep in a large glacier acts plastically, so does rock subjected to large stresses and elevated temperatures. Examples are even known where solid rock at the Earth's surface has deformed permanently subjected only to the stress of its own weight over extended periods of time.
Far from proving a young Earth, the existence of solid rock folded in complex ways proves that stresses within the Earth act over long time periods. Physical and chemical studies of the rock verify that the folding occurred at elevated pressure and temperature - in other words, deep underground. Later, as the land was uplifted and eroded, the rocks were exposed.
I've seen lots of outcrops of folded sedimentary rocks. How would Humphreys explain those where shale and sandstone alternate, with the shale almost always folded and the sandstone partly folded and partly broken? Shale is, as geologists put it, "less competent" than sandstone and more easily folded. But what about the sandstone? Was it solid or not? The folds say "no" according to Humphreys, but the fractures and faults say "yes". Well! I wish these sandstone beds would please make up their mind!
Even more difficult for Humphreys to explain: Igneous rocks are often found folded. Here, the same difficulty is encountered as in the observation of folded ice in glaciers. There are numerous examples of multiple layers of strongly folded volcanic rocks. There is no way you can say they were unconsolidated when folded. Each bed solidified quickly as it was extruded onto the surface before another bed (usually much later in time) was emplaced on top of it. After many layers of rock were formed in this way, and subsequent deposition buried them deeply, forces within the Earth associated with mountain building folded them over long periods of time. If extremely hard igneous rocks can be folded by being subjected to pressure and temperature, then certainly so can sedimentary rocks.
The argument here is that sand from the Cambrian (~540 million years ago) Sawatch Formation, under either tectonic or overburden pressure (or both) intruded into granite along fractures created during the Laramide Orogeny (~70 million years ago). Structures such as these are called "clastic dikes" in analogy to igneous dikes, which are formed when magma intrudes existing rocks along fractures. The sand that was forced into the fractures had to be unconsolidated (loose sand). The Sawatch could not possibly have remained unlithified (lithification = hardened into rock) for nearly 500 million years, therefore, according to this argument, the time gap has to be much less than the 500 million years geologists claim. That is, the Sawatch sand had recently been deposited before it was forced into the fractures.
Unfortunately, the "clastic dikes" in question are in an area (Ute Pass Fault Zone) I am unfamiliar with. Compounding that, I was limited at the time I wrote this in that Texarkana College does not have a geological research library, and I found little scientific information on the Internet concerning this question. (I have found a lot of creationist material, mostly just repeating the Humphreys pamphlet word for word.) Therefore a complete answer to this argument will have to wait until I can track down more information.
However, I did come across one scientific abstract that mentioned these dikes in passing, but put "clastic dikes" in quotes ("Insights on the Kinematic Evolution of the Ute Pass Fault Zone from Investigation of Mesoscopic Brittle Faults" by E. J. Fay et al, presented at the 2004 Denver Annual Meeting of the Geological Society of America), as if that is not what they are really thought to be. I suspect the answer to this question has to do with the sand structures not actually being clastic dikes.
In my geological excursions in Big Bend National Park, Texas, I came across what might be clastic dikes, but more likely some sort of igneous feature. You can find my discussion of these dike-appearing features here.
In the meantime, let me point out that creationists have some much more difficult explaining to do when it comes to sedimentary rocks. An area I am familiar with is the Jackfork Formation in the Ouachita Mountains and its counterpart in Southwest Texas, the Haymond Formation. This sedimentary unit consists of alternating beds of sandstone and shale, amounting to a thickness of up to 6000 feet in the Ouachitas. Alternating beds of sandstone and shale could not have been laid down by a single flood, which would have mixed everything up.
Detailed study of this sedimentary unit shows it was laid down in a marine environment. The sandstones were laid down fairly rapidly by underwater sediment flows called "turbidity currents". The shale consists of silt and clay particles that filtered down through the seawater. Currents would keep the clay suspended except close to the bottom where the water is quiet. So how long would it take a single bed of shale, say 10 centimeters in thickness, to accumulate?
For the answer you have to turn to physics and an equation called "Stokes' law". Undergraduate physics majors are often introduced to this equation when having to perform the Millikan oil drop experiment, an experiment where the charge on an electron is measured. Stokes' law allows you to calculate the settling speed of small spherical particles in a still fluid. This speed depends on the size of the particle, its density, and the density and viscosity of fluid.
Of course, clay particles are not spheres, so they will actually settle out more slowly than Stokes' law would indicate. To compute the minimum time it would take a 10 centimeter shale bed composed of clay particles, say fairly large ones about 2 micrometers across (maximum clay-particle size), to accumulate you can calculate the settling speed assuming a spherical particle shape, then adopt a model for the amount of time it would take the bed to accumulate. Since currents are going to be at work mixing the sediment with the seawater, a reasonable model that minimizes the time of formation of the shale bed might have the sediment initially suspended equally throughout the water column.
Assume a heavy sediment load and let the clay particles be separated by a distance only ten times their size. (This is an order-of-magnitude estimate.) In reality only the clay particles in the quiet water near the bottom would settle out, and the sediment would be supplied gradually from the distant land. However, to make the calculation as simple as possible (and to compute a minimum time), let the sediment be all in the water column at one time and have the currents stop, allowing the entire column to begin to settle. How long would it take 10 centimeters of clay to accumulate according to this model?
Stokes' law gives a settling speed of about 0.4 billionths of a centimeter per second for the assumed particles. According to the sediment-load assumption, there are 10 centimeters of sediment in a 100 centimeter (1 meter) column of water. With the above settling speed, it would take about 80 years minimum for a 10 centimeter shale bed to form. Even if the Jackfork only contains 1000 feet of shale, it would take about 240 000 years for it to accumulate according to the model. But note. The model not only makes assumptions consistent with the minimum accumulation time possible, but also ignores erosion and redeposition, which would greatly lengthen the accumulation time.
There is abundant evidence in the Jackfork of erosion by strong underwater currents, followed by redeposition when the currents died out. Essentially identical processes are occurring at this exact instant (a little attempt for dramatic flair here) offshore in the Gulf of Mexico, particularly in the region of the Mississippi River delta. Chances are, therefore, the model underestimates the accumulation time by at least a factor of 100, but certainly even the minimum time is not consistent with a young Earth. And the Jackfork is only one formation in a series of formations that constitute the sedimentary rock sequence of the Ouachita Mountains, including the Stanley Shale, which is much thicker (over 10 000 feet in some places) than the Jackfork.
This particular argument conjures up some interesting physics and is, in fact, based on the research of a genuine physicist, Robert Gentry, a former researcher at Oak Ridge National Laboratory with a significant record of research accomplishment. Mr. Gentry is also a young-Earth creationist. The research in question involves minerals containing radioactive isotopes (atoms) found as "inclusions" in other minerals. As the radioactive isotopes decay, particles (electrons, anti-electrons, alpha particles) are emitted from the nucleus of the isotope.
The type of isotope an atom is depends on the number of protons and neutrons in its nucleus; the number of protons determines what element the isotope belongs to. For example, the well-known radioactive isotope Carbon-14 has 6 protons, making it a carbon atom, and 8 neutrons, for a total of 14 "nucleons" in its nucleus. The more common, nonradioactive Carbon-12, by contrast, has 6 protons in its nucleus but only 6 neutrons. Alpha particles consist of two protons and two neutrons held together by nuclear forces and are identical to Helium-4 nuclei.These particles are emitted over a period of time in all directions, causing damage to the crystalline structure surrounding the inclusion, eventually producing a "radiohalo" of discoloration due to the damage. In a microscope, these radiohalos are typically circular regions of discoloration centered on the radioactive mineral inclusion. Each type of isotope is thought to produce a different-sized radiohalo such that the isotopes in the inclusion can be identified. Or so the theory goes.
Gentry's argument stems from his study of hundreds of samples of granitic rocks he considered to be "primordial" (that is, the first rocks of planet Earth). In these rocks are biotite and fluorite crystals (biotite is an iron-bearing mica) containing radioisotopes. Gentry claimed that he could identify radiohalos caused by the decay of the isotopes Polonium-218, Polonium-214, and Polonium-210. In a sequence of radioactive decays, Polonium-218 decays into Polonium-214, Polonium-214 decays into Polonium-210, and Polonium-210 decays into Lead-206, which is nonradioactive. These decays result in the emission of alpha particles, presumably contributing to the creation of a particular halo. Hence three separate halos are supposedly created by this decay sequence.
Since Polonium-218 has a half-life of about three minutes, essentially none of it is left after about a half hour; it has almost entirely decayed. In a mineral containing uranium, Polonium-218 (and subsequently 214 and 210) would be produced continually, since it is an isotope along the long chain of decay from Uranium-238 to Lead-206. Gentry claims, however, there is no evidence in his samples of the presence of the decay of the isotopes above Polonium-218 in this chain. That is, the halos associated with the alpha-particle decays of isotopes leading to Polonium-218 are missing.
Gentry argues that this evidence proves the polonium didn't arise from previous radioactive isotopes but was created when the rock itself was formed. Therefore, these "primordial" rocks had to be formed very quickly, in a time much less than thirty minutes, in order for the Polonium-218 halos to appear. This would require a supernatural act of creation, since it takes granitic magma bodies formed naturally thousands of years to cool.
Unlike most others who have commented on this theory, I am dismayed the most by what this argument implies about the Creator, and the nonchalant way creationists accept this implication. Gentry didn't thoroughly document his samples according to geological setting and physical properties, although some are known to have come from a location in Ontario. In any case, the samples came from granitic rock outcrops that give every indication of having been formed as a result of natural processes. How can I say that? Because there are no rock outcrops that look like they were created in place by supernatural processes! (If you know of an exception to this observation, lots of geologists, me included, would love to hear about it.) This implies the Creator is deliberately trying to pull the wool over our eyes by creating rock to look as if it were formed naturally and not by divine intervention. Is this "God as con artist"? And, if the Creator created the granitic rocks to look like something they weren't, maybe the radiohalos were created to mislead as well. Maybe they were just placed there by a God with a strange sense of humor.
Fortunately, we don't have to conclude God is a cosmic practical joker. (For a more exhaustive analysis of the radiohalo controversy, check out the following reference, and the references it cites. I will present a brief version here, which doesn't cover every aspect of the question.) Central to Gentry's argument is an assumption: The granitic rocks from which his samples were taken are primordial, an assumption Gentry does not support by evidence from the field. (And, as pointed out above, it would be futile to look for such evidence anyway. In fact, in the case of the rocks known to be from Ontario, he apparently ignores field evidence which proves the rocks couldn't be primordial.) Either these "primordial" rocks were created at once to look natural or else natural processes were running at an incredible geophysical fast-forward pace. Either way we have a divine scam. A more logical approach is to accept the rocks as the consequence of natural processes and look for a natural explanation for the radiohalos.
So, we ignore the primordial vs non-primordial question and ask, "What about the radiohalos themselves? What caused them? You may consult the above reference for details, but, in short, subsequent research has shown that there is really no proof the radiohalos are formed by the decay of polonium, in particular by the decay of Polonium-218. Nor is it clear the radiohalos result from alpha radiation. This is where the physics gets interesting.
However, assuming the radiohalos do, in fact, result from polonium decay, one explanation that has been put forward is based on the migration of Radon-222 into the "primordial" granites. This theory successfully explains many observations associated with the radiohalo controversy – observations not explained by the creationist theory, unless you want to fall back on a jokster God – and is therefore, philosophically as well as scientifically much preferrable to Gentry's theory.
The theory briefly goes like this. All of Gentry's samples come from rocks closely associated with uranium concentrations, and all of them contain minerals indicating the rocks were formed, not from magma, but from alteration of rocks already there by hydrothermal processes (that is, processes involving the infiltration of extremely hot water containing a variety of dissolved substances).
Uranium is a source of Radon-222, a chemically unreactive gas which is highly mobile and decays into Polonium-218. (Radon-222 is the isotope along the Uranium-238 decay chain just above Polonium-218.) The minerals, particularly biotite, on which the radiohalos are centered, are quite permeable to radon and have sites where the polonium products of radon decay can be trapped. Hence, you get the halos as observed without any isotopic precursors but Radon-222. However, since Radon-222 decays by emitting an alpha particle with almost the same energy as Polonium-218, it would be quite difficult to tell a Polonium-218 halo from a Radon-222 halo. Also, since Radon-222 has a half-life of four days, a significant amount would still be around after a week or two, so that there would be plenty of time for the migration of the radon into the biotite.
This theory also explains the puzzling lack of halos of isotopes of polonium other than the three mentioned so far. It's as if the Creator had a fondness for the polonium isotopes that form in the Uranium-238 decay chain but didn't care for those formed in the Uranium-235 and Thorium-232 decay chains. Radon isotopes are also produced in the Uranium-235 and Thorium-232 decay chains, but these have half-lives much shorter than Radon-222 and therefore do not have time to migrate into the biotite and other minerals that serve as hosts for polonium. Therefore, the polonium isotopes that otherwise would result from the decay of these radon isotopes are not seen, explaining the absence of these isotopes naturally.
This is, of course, "just a theory", but, since it explains the radiohalos more satisfactorily than simply invoking divine intervention and also explains other observations that Gentry's theory cannot explain except by more divine intervention, it is, scientifically, the preferred theory.
As others have pointed out, Gentry's theory has nothing to say about the vast (tens of thousands) of rock samples successfully dated by analysis of the radioactivity the rocks contain. These dates are consistent with each other and are also consistent with the relative sequence of geological events deduced from field studies. From what I have read, Gentry apparently dismisses these dates as due to the variation of half-lives in the past.
Now this is bizarre. It would take a supercomputer (presumably, God wouldn't need one) to vary the half-lives of all the radioactive isotopes over the past several thousand years to make it appear as if the Earth were old when it was actually young. You would have the problem of varying the half-lives in just the right way that the consistency described above is achieved. That would be a feat that would make any odometer-resetting used-car salesman green with envy! (Unless you like to be taken advantage of, I suggest you take your business elsewhere.)
We are, to some extent, back to the "not enough mud" argument. Humphreys claims that the loss of helium to space in the upper atmosphere of the Earth is too slow to account for its production by radioactive decay in the solid Earth if the Earth is as old as geologists say it is. (The helium was originally alpha particles emitted along the decay chains of uranium and thorium.) Again, the assumption is the current rate of loss has always been the same.
However, a more important point turns out to be that the thermal loss considered by Humphreys is probably not the dominant loss mechanism.
The atoms in the upper atmosphere are moving very fast. The so-called "equipartition theorem" of thermodynamics insures that the lighter the particle, the faster it moves. Hence, light atoms such as hydrogen and helium, which are already moving quite rapidly, can gain enough speed in collisions with other atoms to escape earth's gravity and be lost to space. This is the "thermal loss" mechanism.In the upper atmosphere you are above the ozone layer and there is lots of intense ultraviolet radiation from the Sun. If you want a quick tan, this is the place to go (assuming you can tan faster than you burn). UV radiation also knocks electrons off atoms (ionizes them) in the upper atmosphere, including helium, producing helium with a single positive charge. It is this ionized helium (along with ionized hydrogen, oxygen, and nitrogen) that escapes with help from the Earth's magnetic field.
Charged particles in a magnetic field experience a force, called the Lorentz force, that tends to keep them moving parallel to the field. This effect can trap ions and is responsible for the Van Allen radiation belts. However, near the Earth's polar regions, the magnetic field extends out into space, providing a sort of magnetic highway along which ionized particles, particularly fast-moving light ones such as helium and hydrogen, can escape. Although it has been difficult for space scientists to calculate exactly how much helium escapes this way, it would be a much larger flux than the thermal loss, which is the only mechanism considered by Humphreys.
Furthermore, it is not at all clear helium loss (and the loss of other elements for that matter) has been steady over the geologic ages. For one thing, the Earth's magnetic field has undergone numerous reversals in geologic time. Likely the field diminishes to low intensity during these events, which would allow high energy particles to impinge more easily on the upper atmosphere and collide with helium and other atoms, greatly enhancing the rate of loss of these atoms into space. You see that the situation is not as simple as Humphreys would have you believe. Scientific research allows us to make "light" of Humphreys' helium argument.
I'm not sure why Humphreys thinks this is such a strong argument. He asks, "Since we know stone-age people buried their dead, if the stone age lasted as long as archeologists claim, how come we don't hit a bone every time we dig for fishing worms?" (I'm paraphrasing his argument.)
Geologists know it takes special conditions to preserve fossils. Otherwise, you could extend that argument to "how come we don't unearth a T. Rex every time we excavate for a building". Take soil, for example, where bodies are buried. It has plenty of organisms recycling organic material, even six feet under. There is also plenty of moisture and oxygen to react with and degrade organic material. Carbonic acid, dissolved in water, is very good at getting rid of bone. This is why you typically find not much more than organic debris when unearthing people who have been buried for scores of years, unless they have been buried in substantial coffins. (I am personally acquainted with a sad example of this in my mother's family.) However, there is no evidence of a booming sarcophagus industry in stone-age times. People were buried pretty much as unprotected bodies. Why anyone would expect much to remain mystifies me.
Stone-age people were as bright as we are. So, how come it took so long for them to discover that plants grow from seeds? Since agriculture is recent (on the order of 4000 years ago), it stands to reason that the origin of human beings is recent also. That is how this argument goes.
I imagine that stone-age people new well enough that plants grow from seeds. This is not all you need to know, however, to be a successful farmer, and I'm sure there are a lot of farmers who would agree with that. But surely these people were smart enough to figure things out over thousands of years of pre-history, right? Again, I'm sure they were. They were also bright enough to establish modern science and technology, but didn't.
I'm not an anthropologist, but I'm pretty sure establishing an agricultural society was a major undertaking. You need crops to grow. This means breeding the wild ancestors of today's crops until they are advanced enough a population can depend on them to the point they can settle down. It means a reliable supply of water, which requires irrigation in the regions where agriculture arose. As most any farmer knows, rainfall is either not sufficient or not sufficiently reliable in many places where crops can be grown, requiring skill in crop management, even if irrigation is not necessary. It means mastering astronomical knowledge to the point you can figure out when to prepare your fields. (This is why astrologer-priests were so important in early agricultural societies.) It means settling down from your accustomed life of traveling around to where the food is and establishing a complex, interdependent society. (A single farmer can't raise every type of crop or produce everything he needs.) Also, if you transition from a hunter-gatherer society to one that raises crops, you need a way to store and preserve your food. This requires the development of storage and preservation technology.
The Comanches in Texas were smart enough to be farmers. Why didn't they do it? Why did they insist on hunting buffalo and raiding other tribes, some of whom did grow their food? For crying out loud, if they couldn't figure it out for themselves, they could have at least learned from these other tribes. (As you can see, I really can't take this argument too seriously.)
This argument is virtually identical to the previous one. Why did it take people so long to invent writing? Sheesh, I don't know. Why did it take them so long to invent Arabic numerals? and algebra? the invention of which occurred long after writing appeared. Writing seems to have quickly followed the beginning of agriculture. I suspect the cliché, "Necessity is the mother of invention," had something to do with it. Hunter-gatherers didn't have to keep records of what was bought and sold. All they needed were oral traditions, and there are hunter-gatherers that still do that today.
And, I must come back to the point I made above. How come the Comanches didn't invent a system of writing? How come writing, when it did appear in the New World, was so far behind its invention in the Old World? (Maybe the Incas weren't as smart as we think. After all, not only did they not have a system of writing per se – they apparently used the "quipu" to perform much the same function – they didn't use the wheel either.) Again, I can't see how such an argument could be proposed with a straight face.
All of the above arguments are of the "find the loose brick" variety. It is like someone wanting a building condemned and looking for a brick – somewhere, anywhere – that might be a little bit loose as a justification for razing it. The evidence that the Earth and universe are very ancient is overwhelming. Sometimes I can't believe we are still having these discussions. To me, it's like arguing about whether the Earth or the Sun is the center of the solar system. Can't we put this to rest and move on?
Well, the reason we can't is that there are lots of people whose religious beliefs exclude an Earth and universe that are billions of years old. Now, if someone wants to believe the Earth is a mere 6000 years old and that all living things were created in just a few days exactly like they are today, that is OK with me. (I am assuming what appears to be the most common young-Earth doctrine.) I have no problem with that. What I have a problem with is people trying to argue that science proves this is true. No it doesn't! I also have a problem with these people trying to force these unsubstantiated beliefs on the rest of us, by, for example, trying to insert them in school curricula (or by taking out the science, which is just as bad, as far as I'm concerned).
Finally, note that many of the young-Earth arguments require some measure of divine intervention. For example, God would have to make the ocean originally salty in order to pare down the 40 million year time span - required by D. Russell Humphreys' theory quoted above to accumulate its present load of salt - to a few thousand years. Even more disturbing, God would have had to dump hundreds of meters of mud on the ocean bottoms to bring ocean sediment up to speed. (This mud is not flood produced - a flood could never produce the observed stratification - at least not without even more divine intervention.) And again, did God create the light from the Whirlpool Galaxy already on its way to Earth so that we can see it even though it is 31 million light years away?
My thought is, if you have to keep invoking divine intervention in your argument, why not go for the whole enchilada? Have the universe created just like it is today - young in age but, by divine design, old in appearance. The problem, of course, is that you have the philisophical difficulty of a Creator misrepresenting His creation. Maybe the Earth, the universe, your holy writings, you, your memory, and everyone else are only one minute old. By the very nature of this hypothesis (which is, of course, not a scientific one) you can't prove it isn't true.