The age of the Earth is around 4.55 billion years. Is this an indisputable fact? How would you answer a creationist who asked you this? I ask for a reason.
I was recently emailed by a stranger who wrote:
I am a college student taking Geology for the first time and there is a debate amongst the students in class. I am contacting you to assist in settling this dispute regarding the age of the earth.
If given the choice between these two rudimentary statements, would you say that:
(a) It is an indisputable fact that the earth is [around] 4.55 billion years old.
(b) Based on current scientific evidence, the earth appears to be 4.55 billion years old; however, future generations may find evidence that has the potential to either substantiate or refute our current model.
Excellent question. But the answer MUST depend on the threshold for disputability.
Do you think it is an indisputable fact that the Romans invaded Britain? If so, you must say that it is an indisputable fact that the Earth is around 4.55 billion years old.
If you say that this age of the Earth is disputable because, in principle, further evidence might make us change our minds, then you must also say that it is disputable that the Romans invaded Britain.
People often say that this or that scientific fact is uncertain because it is always in principle revisable. But the same is true of ALL our knowledge about the world.
Does this help? Please let me know how this plays out.
I am not satisfied with my answer.
The question uses the rhetorical device of the false dilemma. If I say that the age is indisputable, I am violating the principle that scientific knowledge is open to challenge by new evidence. If I say that it is disputable, the questioner has succeeded in driving a wedge, with scientific orthodoxy on one side, and me on the other, alongside Young Earth creationists. This of course is the entire purpose; people don’t go around asking whether the existence of atoms is indisputable. By refining the issue as I did, I have slipped between the horns of the dilemma. Sound logic, feeble rhetoric; looks like I’m wriggling when faced with a straightforward question.
What else could I have said?
Mosaic, Fishbourne, image by Charlesdrakew – Own work, Public Domain, https://commons.wikimedia.org/w/index.php?curid=4755271
Post featured in this Sunday’s Herald, here
If you thought (like the books handed out to the children in Kirktonholme Primary) that dinosaurs were almost wiped out in the Flood and then used as beasts of burden until finished off by Nimrod the Mighty Hunter, I have news for you. We have a real live dinosaur sitting in the Scottish Parliament.
John Mason, MSP for Shettleston and a member of the governing Scottish National Party, has just tabled Motion S4M-12149, asking the Scottish Parliament to resolve that
… some people believe that God created the world in six days, some people believe that God created the world over a longer period of time and some people believe that the world came about without anyone creating it; considers that none of these positions can be proved or disproved by science and all are valid beliefs for people to hold, and further considers that children in Scotland’s schools should be aware of all of these different belief systems.
John Mason’s challenge to me and pretty well every other scientist on the planet: prove the world was not created in six days. Now here’s my challenge to Mr Mason: prove you are not a dinosaur.
What is the evidence that you are not a dinosaur? Why is it not a valid belief for people to hold that you really are a dinosaur? How does the evidence compare with the evidence against a 6-day creation from geology, physics, astronomy and cosmology, geography, and I haven’t even started on the fossil record or molecular biology. I have decided that I believe, as a matter of faith, that you really are a dinosaur, and I maintain that this is a valid belief for people to hold, and further consider that children in Scotland’s schools should be aware of this different belief system.
Off the top of my head, the evidence from geology presented by the geologist (later Bishop) Nicholas Steno in 1669, who established the science of stratigraphy. The evidence of Siccar Point, one of the most famous locations in Scotland, where rocks have been laid down, tilted, eroded, and covered by more rocks, as described over 200 years ago by the geologist (and theist) James Hutton. The evidence of the geological column, established during the 19th century by clergyman-geologists like William Buckland and Adam Sedgwick. Other evidence for lengthy processes between geological events, like the weathering at the Giants’ Causeway.
Physics: radiometric dating, first used by Rutherford and colleagues over 100 years ago, and checked and cross-checked many thousands of times since, using different isotope pairs. (And how do we know the clock runs true? Because, since the work of George Gamow in 1928, we have known that decay rates depend on fundamental physical constants, and if they had been different, so would the laws of physics and chemistry and we wouldn’t have the rocks anyway.)
Astronomy and cosmology: around 1920, the Jesuit priest Georges Lemaitre had worked out (although Edwin Hubble gets most of the public credit) that the further away galaxies are from us, the faster they are receding. So running the film backwards, we infer an initial Big Bang (or, as Lemaitre called it, “Primal atom”) where all the matter in our Universe was aggregated at a single point. And according to the best curreent estimate, that took place 13.8 billion years ago, with a further 9 billion years needed to get from there to the processes forming our own Solar System. Making 6 days wrong by a factor of around half a trillion.
How about helioseismology? We can observe vibrations spreading throughout the Sun, use the data to infer how much of the Sun’s original hydrogen has been converted to helium, and calculate how long this would have taken. The answer comes out at 4.5 billion years, which is also the age of the Solar System as inferred from radiometric dating.
As to how far we know the galaxies to be, we can work that out by looking for supernova explosions. Simplifying slightly [I have to say that, because if they find any detail out of place the Creationist shout “Gotcha!”] all supernova explosions of a certain type release the same amount of energy. And apparent energy depends on distance. And we know that the speed of light hasn’t changed, because we can make sense of the patterns of light emitted by the most distant stars, so the laws of physics that dictate the speed of light haven’t changed since the light left these galaxies.
So we know that we have seen galaxies 12 billion light-years away. Which means that they’ve been receding from us for 12 billion years. Not 6 days.
Geography: we have the facts of plate tectonics, as shown by the movement of continents (which we can now follow directly by satellite), and confirmed by palaeomagnetism, showing how the earth’s plates have moved relative to its magnetic field. The reasoning is so simple that a child can follow it, and in fact I’ve reviewed a children’s book that explains it.
And remember, we haven’t even started on the fossil record, or the life sciences.
Now the evidence that John Mason is not a dinosaur. Pretty thin by comparison. Comparative anatomy? If you accept that, you will also have to accept that comparative anatomy shows we’re chimps, with some twenty or so known extinct species more or less intermediate between us and our last common ancestor with the other two surviving chimp species. Physiology and molecular biology? Tush! Go with that, the same kind of evidence as we use in our law courts to establish family relationships, and you end up second cousin to a monkey and fourth cousin to a mushroom. Not what you have in mind.
Intelligent behaviour? On present showing, pit you against a velociraptor and my money’s on the ‘raptor, every time.
And so I think all Scottish schoolchildren, or at a very minimum all schoolchildren in Mr Mason’s constituency, be made aware of the theory that Mr Mason is an Intelligently Designed dinosaur. Otherwise we risk bringing them up with closed minds; minds closed against what we know from overwhelming evidence to be utter absurdities. And that would never do.
Lord Kelvin (Smithsoinian Instituion Libraries collection)
Kelvin calculated that the Earth was probably around 24 million years old, from how fast it is cooling. Rutherford believed that Kelvin’s calculation was wrong because of the heat generated by radioactivity. Kelvin was wrong, but so was Rutherford. The Earth is indeed many times older than Kelvin had calculated, but for completely different reasons, and the heat generated by radioactive decay has nothing to do with it.
Disclosure: in my introduction to the Scientific American Classic, Determining the Age of the Earth, and elsewhere, I have like many other authors repeated Rutherford’s argument with approval, without paying attention to Rutherford’s own warning that qualitative is but poor quantitative, and without bothering to check whether the amount of heat generated by radioactivity is enough to do the job. He thought it was but we now know it isn’t. It was only when chatting online (about one of the few claims in the creationist literature that is even worth discussing) that I discovered the error of my ways.
On the face of it, things could not be plainer. Kelvin had calculated the age of the Earth from how fast heat was flowing through its surface layers. An initially red hot body would have started losing heat very quickly, but over geological time the process would have slowed, as a relatively cool outer crust formed. His latest and most confident answer, reached in 1897 after more than 50 years of study, was in the range of around 24 million years.
Yet on May 20, 1904, there was Rutherford, at the lectern of the Royal institution, talking about a piece of Cambrian rock, and announcing, on the basis of how much of its uranium had decayed to give lead and helium, that its age was some 500 million years. We even have Rutherford’s much quoted account of what happened next:
I came into the room which was half-dark and presently spotted Lord Kelvin in the audience, and realised that I was in for trouble at the last part of my speech dealing with the age of the Earth, where my views conflicted with his. To my relief, Kelvin fell fast asleep, but as I came to the important point, I saw the old bird sit up, open an eye and cock a baleful glance at me.
Then a sudden inspiration came, and I said Lord Kelvin had limited the age of the Earth, provided no new source [of heat] was discovered. That prophetic utterance referred to what we are now considering tonight, radium! Behold! The old boy beamed upon me.
This all seems clear enough. Rutherford is referring to Kelvin’s cooling argument. But this argument is invalid, because it assumes no new source of heat, and such a source exists, namely radioactivity.
The process that was overlooked in Kelvin’s calculations was also, indirectly, responsible for producing these folds.
Or so says the popular myth. The truth is more complex, and more interesting. For a start, Kelvin’s “prophetic utterance” did not refer to the Earth at all, but to a separate calculation of the age of the Sun. We know how brightly the Sun shines, and hence how rapidly it emits energy. If we knew how much energy it had to start with, and assumed that it wasn’t being added to, we could simply divide the initial amount by the rate of depletion, to estimate how long it would be able to shine. Kelvin performed such a calculation many times. As source of energy, he invoked the most intense source known to him, namely the gravitational energy released when the Sun collapsed from a diffuse cloud of gas to its present size. This led him to conclude in 1862 that the age of the Sun was in the range of 10 million to 100 million years (subsequently refined to around 20 million), and that “inhabitants of the earth can not continue to enjoy the light and heat essential to their life for many million years longer unless sources now unknown to us are prepared in the great storehouse of creation [emphasis added].” These are the prophetic words that Rutherford was referring to.
If Rutherford thought that the energy of radioactive decay was fuelling the Sun, he was greatly mistaken. The philosopher Auguste Comte had written in 1835 that we would never know the internal composition of the heavenly bodies. He was wrong. Pass electricity through a gas or vapour, and it will emit light at specific frequencies that depend on the elements present (one familiar example is the sodium yellow of street lights). There are dark lines in the solar spectrum, and by 1860 the German chemist Kirchoff had shown that their frequencies match these characteristic emission lines. So the chemical composition of the Sun’s outer layers was already well-known, and the fractional abundances of the heaviest elements, including almost all those that exhibit radioactivity, are quite negligible. And we now know, as Rutherford could not, that radioactive decay does not generate enough energy. Even if abundant supplies of the radioactive elements were concealed within the Sun’s interior, they would not suffice to fuel the Sun for Rutherford’s 500 million years, let alone the 4,500 million years, with as much still to come, required by current estimates. It was not until 1920 that the source of the Sun’s energy was correctly identified as the fusion of hydrogen to helium, and while this was soon generally accepted, quantitative confirmation by measurements on the neutrinos produced had to wait until 2001. Using Einstein’s famous mass/energy equation and the masses of the isotopes involved, it is easy for us to calculate that the fusion of hydrogen to helium is some thirty times more productive of energy than the decay of the same mass of uranium to helium and lead; but Rutherford in 1904 could not have known of the relationship between mass and energy, or the precise masses of the relevant isotopes, or even that such things as isotopes existed.
But what about the age of the Earth itself, and Kelvin’s cooling calculation? This is what I had for many years assumed that Rutherford was talking about, and it turns out that radioactive decay is no real help here either. Measurements on granite in the early years of the 20th century suggested that radioactivity could fully account for the amount of heat being radiated out to space, and that the Earth might even be heating up. But we now know that granite is not representative of the Earth as a whole. The total rate of heat production by radioactive decay is currently estimated at around half the amount that the Earth emits to space, so simplemindedly we might imagine that this extends Kelvin’s calculation by a factor of two. Maybe a bit more, since by their nature radioactive materials would have been more abundant in the remote past, but this will not make much difference over the few tens or even hundreds of millions of years then under discussion. And even this grossly exaggerates the potential significance of radioactive heating, since all we need to consider is the heat generated in the outermost layers, from which heat has had time to diffuse the surface.
So how could Kelvin’s cooling argument be refuted? The correct argument had been put forward a decade earlier, before radioactivity had even been discovered, by John Perry, one of Kelvin’s own former pupils, and Kelvin had partly accepted the principle of Perry’s reasoning.
To understand what is really happening, we need to consider the different ways in which heat can be transferred. You may remember from school that there are three processes available; radiation, conduction, and convection. Radiation is the process by which the Sun, or the filament of an incandescent light bulb, glows yellow hot; or at lower temperatures the embers of a fire or the coals of a barbecue glow red hot; or, at yet lower temperatures, the Earth loses energy to the coldness of outer space by glowing in the infrared. It is not really relevant to the transmission of energy through opaque material such as rock. Conduction is simply the diffusion of heat through material, as the faster moving atoms of the hotter region jostle against, and share their energy with, their cooler neighbours. The third, and most efficient, heat transfer mechanism is convection. This is the physical movement of hotter material, carrying its heat with it, as in the roiling that takes place in the water when you boil an egg on a stove, or the pattern that forms in the film of oil in the pan if you prefer your eggs fried. Hotter material expands, making it less dense, so it rises to the surface, bringing cold material closer to the heat source.
Convection in a pan over a heat source. Warm (red) material is less dense and rises, allowing cold (blue) material to sink. Image by Eyrian through http://en.wikipedia.org/wiki/File:ConvectionCells.svg
Radiation is only relevant when we are talking about the transfer of heat through empty space, or through some transparent medium. Diffusion is simply the statistical spreading out of the extra heat in the hotter material, and is an inefficient process over long distances. By far the most efficient heat transfer mechanism is convection, but this can only take place in a fluid, where hotter and colder material can physically change places.
Back to Kelvin’s cooling rate calculation. This depended, among other things, on assuming heat transfer by conduction, and the rate of conduction was determined by actual measurements on rocks. Now imagine what would happen to Kelvin’s calculation if the actual heat transfer process were more efficient than this. The effect is the opposite of what you would at first imagine. Commonsense suggests that more rapid heat transfer would imply more rapid cooling. Not so. If heat transfer is limited, only a relatively shallow layer near the surface will have had time to contribute. If heat transfer turns out to be more efficient, the cooled layer will be correspondingly thicker, heat will have been conveyed from greater depths, and the total amount of heat conducted through the surface and lost to space will be correspondingly greater. But we know the total rate at which heat is being transferred, from the conductivity experiments and the rate at which temperature increases when we go down a mine, and this acts as a constraint on the calculation. Fixed rate, but a greater total amount because of more efficient heat transfer, implies a longer time. The cooling calculation can therefore be brought into line with Rutherford’s results, and indeed with the even longer times that we now know to be involved, if heat at depth is sufficiently more mobile than Kelvin had imagined.
In 1894, Kelvin’s former pupil and protégé, John Perry, had suggested higher heat transfer as a way of reconciling Kelvin’s age estimates with the hundred million years or so then required by the geologists. Kelvin, rather grudgingly, agreed in principle, and undertook to examine whether the thermal conductivity of rocks did increase as required at high temperature.  Within a few months, Kelvin reported a colleague’s response to this question; they did not. Indeed, Kelvin took the opportunity to review the entire question in the most extreme possible light, triumphantly lowering his best estimate of the age of the Earth to around 24 million years, noting that this was in good record with his estimates for the age of the Sun, and claiming that the burden of proof was now back with the geologists. Perry, in reply, drew attention to the fact that Kelvin had totally ignored the possibility that the Earth’s interior was or had been fluid enough to support convection, but Kelvin seems to have passed over this suggestion in silence.
A pity. Convection in the mantle, as we now call the region between the solid crust and Earth’s metallic core, is a cornerstone concept of modern geology. The implications of this, together with an explanation of why Perry waited until 1894 to challenge Kelvin’s calculations (which went back, as we have seen, to 1862 and earlier), and how I belatedly stumbled upon this story as a result of chatting online about the creationist literature, will be the subject of further posts.
An earlier version of this post was published in 3 Quarks Daily
 Comte, Positive Philosophy, Bk II Ch 1
 Annalen der Physik 185, 148–150, 275-301 (1860).
 Some radioactive elements, such as the newly discovered radium that Rutherford was referring to, do generate heat quickly, but that is because of their rapid decay rate, which implies short half-lives and rules them out as candidates.
 Perry, Nature 51, 224-227 (1895); Kelvin’s acknowledgement is at p. 227, his dismissive rebuttal at p. 438, and Perry’s final attempt at persuasion at p. 582.
The Rev David Blunt is Minister at North Uist and Grimsay Free Church of Scotland (Continuing), Bayhead, North Uist, not to be confused (Heaven forbid!) with the benighted folks at North Uist, Grimsay, and Berneray Free Church of Scotland, Carinish.
He subscribes to a catechism that states that unless God arbitrarily decides otherwise, I (he, too, come to think of it) am “foreordained to dishonour and wrath, … to the praise of the glory of his (God’s,not the Reverend’s) justice” because of the guilt of Adam’s first sin, rendering us liable to “everlasting separation from the comfortable presence of God, and most grievous torments in soul and body, without intermission, in hell-fire for ever.”
If he really believes that that is what he believes and preaches, that is no one’s business but his own and his congregations (although I would have grave misgivings should he be preaching such sadistic doctrine to children.)
The Reverend also believes that the devil seeks to confuse us through the teaching of evolution, and that everything was created over a period of six days, and in order to justify this belief he takes from time to time to the pages of the Hebridean News, where he tells us that
The notion that evolution is responsible for a process of development in living things, beginning with microbes and leading ultimately to men, must be rejected as there is not a single proven fact to support it.
I initially responded,
The Rev David Blunt says that “there is not a single proven fact” to support evolution. If he goes to the website http://www.talkorigins.org/faqs/comdesc/ he will find, spelt out in detail, 29 separate arguments and hundreds of supporting facts that show that evolution is true. If he goes to the Biologs website, and looks up Dennis Venema, he will find a brilliant explanation of all this by a devout evangelical.
If the Rev does not choose to inform himself about the facts,that is his business. But he denies their existence, he is bearing false witness.
The Reverend is clearly a fast reader, since within two days he had digested the 60 or so sections in talkorigins, and Dennis Venema’s excellent 28-part series. And so he was able to reply:
The sort of ‘facts’ which are essential for the theory of evolution to be true include the following: the existence of mutations representing the increase in genetic information necessary to arrive at more advanced life forms; the existence of life forms (extant or extinct) which are obviously transitional in character; the existence of billions of years of time.
Mutations … overwhelmingly detrimental… We still look in vain for specimens which are intermediate between one life form and another. The fossil record, which Darwin expected to provide examples of missing links, has yet to yield them.
Aeons of time are crucial to the theory of evolution yet it cannot be proved that the earth is billions of years old: indeed many scientific facts point to a much younger earth… [Evolution] must be able to account not simply for microbes to men but molecules to men – or even more precisely – particles to people. In other words it must be able to explain how life can arise from non-life. That is a real leap of faith!
There is no observable evidence for the theory of evolution. It is not testable over time and cannot be verified.
To pretend that biological evolution has to include an explanation of the origins of life is at best mistaken, at worst dishonest. Consider that before the 1950s, we did not know the origin of atoms. Nonetheless, atomic theory had been the central concept of chemistry since before the 1820s. Similarly, we do not know the origins of life, but evolution has been the central concept of biology since before the 1870s.
No one doubts that most mutations are harmful. A few of them do increase fitness. Harmful mutations are bred out, while fitness-enhancing mutations spread. It’s really that simple. Indeed, the whole of plant and animal breeding is one vast demonstration of evolution, albeit evolution directed by us rather than by the pressures of the natural environment. The Rev Blunt admits the occurrence of evolution under the pressure of artificial selection. How then can he claim that it is in principle impossible under natural selection, or that evolution has never been verified?