by Ted Nield
Are changed and bowed beneath the ills
Of ice and rain, of river and of sky;
The sea that riseth now in agony
Is not thy sea. The stormy voice that fills
This gloom with man’s remotest sorrow shrills
The mem’ry of thy lost futurity.
Joly, like many a geologist before and since, grew a little giddy staring into the abyss of time, but the uneasy truce over the depth of that abyss finally collapsed when Kelvin revised his estimate of the Earth’s age downwards from 100 million to twenty million years. Joly knew there could now be no reconciling Kelvin’s conclusions with geologists’ gut feeling that the planet simply had too much recorded history to be squeezed into such a short span. Joly attempted to find another way; to search for a different quantitative approach, whose conclusions were not (like Haughton’s) open to such differing interpretation, and which could offer a more probing test of Kelvin’s conclusions. Independently, he hit on an idea first suggested by Edmond Halley (1656–1742), the first man to predict the return of the comet named after him.
Halley had had different motives from Joly. Although Halley also wanted to expand the amount of time available for geological processes (he was looking for a few thousand years extra), his other objective had been to refute a different, to his mind more dangerous (and much older), idea: namely, that the world was eternal. Halley was not simply trying to burst bonds imposed by Christian dogma but, within that framework, to refute the Greek philosopher Aristotle’s idea of an ahistoric, eternal Earth. Aristotle’s world without beginning or end, oddly reminiscent of Hutton’s nineteenth-century version (‘no vestige of a beginning, no prospect of an end’) had always offended Christian tradition, because (to use Archbishop Ussher’s words) it ‘spoileth God of the glory of His creation’.
Just as Kelvin’s method was based on two central assumptions – that the Earth was cooling down from an original molten mass, and that no new heat had been added since – Halley’s and Joly’s idea presumed that the Earth’s first ocean had been freshwater, and that all the salt now dissolved in it got there by being washed off the land. If Joly could find out four things – the volume of the ocean, the average concentration of salt in it, the amount of water coming down all the Earth’s rivers, and the amount of salt contained in that – then he would have all the information needed to calculate how long it had taken for the rivers to put all the salt into the ocean, and thus discover the age of the Earth.
If this sum is done carefully, accounting for all the reverse mechanisms that may return salt to the continents (such as the creation of shallow evaporating seas like the Zechstein) what it actually measures is the average residence time of a sodium atom in the ocean. That is neither an uninteresting nor trivial fact, and the correct average figure is probably around 250 million years, or about the same time that has elapsed since Pangaea began to break up. Unfortunately, it has nothing whatever to do with the age of the Earth. Halley’s and Joly’s initial assumptions were just as wrong as Kelvin’s.
However, Joly did not know this; and when he performed the calculation he came up with an estimate of eighty-nine million years, which was near enough ninety million, which seemed near enough to the 100 million years that geologists had got used to before Kelvin reduced his estimate. When Joly published this research with the Royal Dublin Society in 1899, it was hailed immediately. What was more, geologists (who had chafed under Kelvin’s yoke for long enough by this time) at last saw the good Lord being tackled on his own, quantitative, terms – and found it good.
Kelvin’s reign was not to last; though, instead of succumbing to attack from without, his chronology collapsed from within. The dawn of the new century brought interesting times for physics, when, with the discovery of radioactivity, subatomic particles and relativity, physicists suddenly realized they actually knew a lot less about the world than they had thought. Radioactive decay not only provided the tools to solve the age of the Earth problem once and for all but gave the planet the independent internal source of heat that fatally wounded Kelvin’s method and made his hitherto infallible conclusions seem as nonsensical as Archbishop Ussher’s. Joly, who corresponded with all the great physicists of his time, was well up to speed with the new thinking. He quickly saw that the Earth could at last be very old indeed. You can sense the excitement in his writing: ‘No! The slow exhaustion of primitive heat has not been the history of our planet. Our world is not decrepit by reason of advancing years. Rather we should consider it as rejoicing in the gift of perpetual youth …’
And he went on: ‘Endlessly rejuvenated, its history begins afresh with each great revolution.’
Joly’s halo
Joly’s first great insight into the uses of radioactivity concerned something he and other geologists had seen under the microscope, in rocks cut in thin section so that light could pass through and allow all the mineral crystals within to be identified.
For some time it had been observed that crystals of a kind of mica called biotite, which has a beige-brown colour in transmitted light, sometimes seemed to exhibit a rash of dark, circular spots that looked rather like some virus infection on the leaf of a plant. Minerals under the microscope can change their colour when the viewing stage is rotated in polarized light, a phenomenon known as pleochroism. The puzzling spots therefore received the lovely name of pleochroic haloes.
Before the discovery of radioactivity, it was thought that the haloes must result from chemical diffusion of some sort, from whatever lay at the halo’s centre, rather like an ink drop on blotting paper. Looking carefully at the haloes, however, Joly realized that this could not be. The haloes were not just fuzzy diffuse blots but were made up of many concentric rings, more like the rings of Saturn. In three dimensions, what presented to the microscopist as two-dimensional rings were, in fact, spheres; and Joly was the first to realize that they formed because a radioactive source at their centre had been sending out high-velocity particles into the surrounding crystal. The colour change was an optical distortion caused by the microscopic damage inflicted by these emanations. What was more, the concentric rings represented different travel times within the surrounding lattice, which meant that different kinds of radiation were being emitted, each with different powers of penetration. From this Joly deduced that it should be possible to work out what the radioactive element was that had given rise to the haloes, since each radioactive element has a distinctive radiation signature.
And so it was that Ireland nearly entered the Periodic Table of the elements, because much of Joly’s data defied ready analysis and at one stage he mistakenly thought that he had detected a new element with a hitherto unseen radiation signature. He proposed the patriotic name of Hibernium for this new element; but alas, it turned out that the element in question was already known.
Most pleochroic haloes in biotite are caused by tiny crystals of the mineral zircon enclosed within the mica. Zircon, often used today in jewellery as a substitute for diamond, is chemically zirconium silicate, but within its crystal lattice it is quite common for some zirconium atoms to be replaced by atoms of the naturally occurring radioactive elements uranium and thorium.
Joly, always on the lookout for a new physical measure of the Earth’s age, also had the idea that he might be able to use the haloes to date the rocks that contained them. Reviewing various dating methods in 1914 he wrote:
The time required to form a halo could be found if on the one hand we could ascertain the number of alpha rays ejected from the nucleus of the halo in, say, one year, and, on the other, if we determined by experiment just how many alpha rays were required to produce the same amount of colour alteration as we perceive to extend around the nucleus.
The latter estimate is fairly easily and surely made. But to know the number of rays leaving the central particle in unit time we require to know the quantity of radioactive material in the nucleus. This cannot be directly determined. We can only, from known results obtained with la
rger specimens of just such a mineral substance as composes the nucleus, guess at the amount of uranium which may be present.
Working with Ernest Rutherford, Joly published the results of this method in 1913, using uranium haloes in micas from County Carlow. The research, he wrote, suggested ages of ‘from 20 to 400 millions of years’; the halo method, also, was disappointingly vague. But it was, at least, pointing in the right direction. The rock in question was actually about 375 million years old.
But Joly’s inventive mind had spotted still more implications of radioactivity for geology. He had realized that more heat was being generated under the continents than was actually being caught in the act of escaping.
In his 1924 Edmond Halley lecture to Oxford University, ‘Radioactivity and the surface history of the Earth’, Joly told his audience how radiogenic heat had a tendency to build up beneath the insulating cover of the Earth’s continental crust. If that went on unchecked, something would have to give. After hundreds of millions of years, Joly believed, rocks deep under the continents would start to melt. The overlying crust would then break up and massive outpourings of lavas – such as are seen in India’s Deccan Traps, or the older Siberian Traps, whose eruptions coincided with the breakup of Pangaea – would herald a period of great tectonic instability and fluidity, even rendering possible the outlandish idea of continental drift.
Two years later Joly sat in his study in Trinity College’s Museum, writing his contribution for van der Gracht’s symposium volume. Though his powers as a scientist were diminishing, he remained open to new ideas and wrote that his theory of recurring cycles of sub-crustal melting now threw the question of continental drift wide open. Offering van der Gracht what support he could, he wrote that the acknowledged fact of radiogenic heat meant that it was now at last ‘legitimate to enter upon the problems arising out of continental movement’.
Joly had realized that radiogenic heat, building up inexorably inside the Earth, governed the way the Earth’s great heat engine worked. Like all the best scientific ideas, it was incredibly simple. All it needed was the continuous generation of heat, and a thermal blanket to stop it getting out. Van der Gracht noted with satisfaction: ‘If radioactive heat does accumulate in the manner discussed, a periodic displacement of the blanketing Sial floats [continents] becomes a requisite …’
Today Joly’s mechanism is still the accepted basic explanation of why supercontinents break up. A supercontinent sits over the warm Earth like a fur cap sits on your head, holding in heat. However, unlike a fur cap, eventually the supercontinent must break up because the heat has nowhere else to go but up and out. Magmas generated at depth break through the crust and create massive outpourings; convection rising deep below the continent tears it into many smaller landmasses, and sends them off like flotsam in a stream. New oceans begin to open within the supercontinent, whose fragments then, at the speed of your growing toenails, either race all the way around the globe to meet one another on the other side (extroversion), or stall and shrink back on themselves, consuming the young interior oceans in the process as Tuzo Wilson predicted (introversion).
Of this great cycle of the making and breaking of continents, Wilson glimpsed a part. Before him, John Sutton, with his clustered radiometric dates from the Precambrian, outlined the whole. But almost forty years before the plate-tectonic revolution, John Joly already had the explanation of why the Earth’s grandest pattern operated: by predicting it from basic physics.
The wrong-way telescope of time, which makes the distant seem more distant still, has rendered Joly a sadly diminished figure in our view of history. Yet, if Wegener had discovered a phenomenon looking for a mechanism, Joly discovered a mechanism in search of a process, conceiving an idea that would sleep in the literature until its time was right. Perhaps now that Joly, who also published on possible life on Mars, has had a crater there named for him, the time is right to add to this the honour of the earthly Supercontinent Cycle; for it was his vision that predicted it, and still drives it.
The poet in him certainly rejoiced that the dull fate of gradual heat-death did not, after all, await our beautiful planet. He wrote presciently: ‘Our geological age may have been preceded by other ages, every trace of which has perished in the regeneration which has heralded our own … a manifestation of the power of the infinitely little over the infinitely great – the unending flow of energy from unstable atoms wrecking the stability of the world.’
Our planet had, Joly saw, an inner life: a life whose warmth demanded a long-term cycle of tectonic activity. Like Halley’s comet, supercontinents would keep returning. Mother Earth had a pulse.
9
MOTHERLAND
This film is based on real myths.
NICOLAS CAGE (ATTRIBUTED)
Genesis
In 1934, four years after Wegener met his death on the Greenland icecap and drift theory was perhaps at its lowest ebb, cosmic forces were at work. They were busy causing a set of divinely inspired papers to be translated from the ineffable language of the Universal Father into English, by a complex series of intermediary processes administered by an ‘editorial staff of superhuman beings’.
At least, that is the view according to followers of the resulting tome, known as The Urantia Book. Like other new religions, its followers make the claim that the teachings contained in its 196 papers are literally true. As Harry McMullan III writes in his introduction to The Urantia Book, it ‘claims to describe reality as it actually is’.
Describing reality as it actually is is, of course, what scientists think they are attempting, though as a rule, if the results involve superhuman beings at all, they tend not to set much store by them. Rather, scientists rely on thinking things out for themselves, producing original ideas that explain, as closely as they can manage, the phenomena they observe. As the motto of the world’s oldest scientific society, the Royal Society of London, has it, ‘Nullius in verba’, or, loosely translated, ‘Take nobody’s word for it’ – and by nobody they really do mean nobody.
It is quite the reverse of the revelatory approach, where in the beginning there always tends to be somebody’s Word, which tends always to be with the writer, celestial or otherwise, and with which there can therefore be no argument.
So how spooky must it have been for geology professor Mark McMenamin of Mount Holyoke College, Massachusetts, to discover in 1995 that much of his work to date had apparently been predicted by a sleep-talking mystic from Illinois claiming to be in contact with a Universal Father and his superhuman editorial department?
Mark McMenamin researches rocks from another time, long before the time of Wegener’s Pangaea, when all (or most) of the continents were fused into one giant mass. It was also McMenamin who, in notes from 1987, first hit upon a name for it, calling it Rodinia, which he published in a book written in 1990 with his wife Dianna called The Emergence of Animals – the Cambrian Breakthrough. By the mid-1990s the name had stuck, particularly (one suspects) because so many of the scientists who work on rocks of this age are Russian. For it derives from the Russian noun rod, meaning family or kin; hence the Russian verb roditz, which means to give birth to, which in turn gives rise to the noun rodina, meaning birthplace, or native land. The McMenamins’ Rodinia was the supercontinent around whose shores, and during whose fragmentation, complex life first evolved towards the end of the Precambrian.
Native lands are important to us all, whether we happen to be a French Huguenot living in South Africa or the USA, or a Jewish Viennese born in London. Ultimately the concept is meaningless because, somewhere along the great chain of being, everyone has come from somewhere else. But we are all products of the evolution of complex life. Rodinia is the oldest known supercontinent upon whose former existence scientists more or less agree, and so Rodinia can indeed be said to be the birthplace of us all – and of every moving creature upon the Earth.
Urantia
In 1995 Mark McMenamin made an extraordinary fossil find while doing fieldwor
k in Sonora, Mexico. It turned out to be the oldest known example of a group of enigmatic, long-extinct fossil creatures, which existed before the major divisions of the Animal Kingdom, as we know them today, came into being. He had found the world’s oldest Ediacaran fossil.
Nobody really knows what the Ediacarans were, so opinions on the subject among palaeontologists are strong and divided. When I was a student in the 1970s they were known from just a few places worldwide, including Charnwood Forest in the UK and the Ediacara Hills in the Flinders Range of South Australia, after which they were named. But these rare discoveries had occurred in the 1940s and 1950s. Ediacarans were rare, perplexing and, above all, famous. New finds were like hen’s teeth.
So there was great excitement in 1977 at Swansea University when one of my lecturers Dr (now Professor) John Cope – a man whose fossil-finding talents are almost supernatural – discovered some new examples of these creatures right on our doorstep just a few miles from the sleepy market town of Carmarthen. The find was also completely unexpected, as it came from rocks that the Geological Survey had long previously mapped as Ordovician, and was made as part of a mapping project that Cope had begun with a group of amateurs. Needless to say, as soon as the find’s full significance was realized a mechanical excavator was brought in. The whole lot was shipped back to the university for painstaking professional research and a preliminary note of the find to be made in Nature.
Ediacaran forms – some palaeontologists feel unable to say for certain whether many of them were animals at all, in the modern sense – display a variety of body plans. To be sure, some may have been the ancestors of later animal groups such as the trilobites; but others seem to show no obvious affinity with any other animal, living or fossil. This was a moment in Earth history when many different forms of life evolved, some highly peculiar when seen alongside modern life, and seemingly showing little or no kinship with anything we would feel comfortable calling either animal or plant.