Supercontinent: Ten Billion Years in the Life of Our Planet (17 page)

But a number of plausible mechanisms
were
on offer at the time, one of which – convection currents in the Earth’s mantle, driving the continents around like scum on a slowly roiling pan of pea soup – had existed in the literature since 1839. It had been used as a possible explanation for surface features since 1881, in
The Physics of the Earth’s Crust
, the first geophysics text ever written, by the Reverend Osmond Fisher (1817–1914). Nor had they been forgotten. Convection currents below the Earth’s crust were forcefully advocated through the 1920s by British physicist turned geologist Arthur Holmes (1890–1965). Also, calculations comparing the probable
viscosity
of mantle rocks accorded well with the speed of the isostatic uplift of Scandinavia after the retreat of the ice sheets, and the rate of movements seen across big faults like the now-famous San Andreas in California. Important work using scaled experimental models (rotating cylinders in tanks full of goo covered with thin skins of wax) was carried out in the 1930s and produced some highly suggestive results.

Indeed, mantle convection is the model geologists still favour today. Yet despite the development of a much-refined model since Holmes’s day,
direct
evidence for convection remains elusive. In other words, today ‘the mechanism’ remains a mystery, but it no longer matters. Because geophysicists have proved with evidence of their own that the continents can and do move sideways, the mysterious mechanism has changed from an insuperable objection to a
legitimate
subject for research. This means that Charles Ray was right. Many distinguished geologists
had
proposed plausible mechanisms. The acceptance of Wegener’s theory did not fail, at least, for lack of convection!

Comparing drift to another geophysical phenomenon, the Earth’s magnetic field, helps to show why the ‘no mechanism’ argument once seemed so powerful. Before the 1940s, when one was finally
discovered
, the lack of a mechanism for creating the Earth’s magnetic field had never dented belief in its existence because scientists could
measure
it directly. Du Toit’s work in Brazil merely provided a better class of the same circumstantial evidence, as did Henno Martin much later when he published on the mirror-image glaciation evidence from Namibia and Brazil. The question was, if the continents were drifting, how could you measure it
directly
?

The scientific world was also moving away from the descriptive, personal methods employed by field geologists like du Toit. America particularly was falling in love with methods that removed the observer from the equation – that ‘objectified’ observations – rather than demanding the expert view of seasoned experience. Anyone could see the similarity of the opposing coastlines of the Atlantic – just as Ortelius, the first man to see the evidence, had done in his great world map of 1570. He, Alfred Wegener and the mythical ‘any
schoolboy
’ could leap to the same conclusion. But if, on the other hand, a
computer
did the matchmaking and confirmed the closeness of the fit,
that would be different. And indeed it was, when in 1965 the first computer-matched transatlantic fit was published. The mirror image coasts were no longer dismissible as mere coincidence, a meaningless picture in the clouds. A computer doesn’t find patterns where none exist; it doesn’t do things by eye or use artistic licence; it applies Euler’s Theorem, and doesn’t care about the outcome.

Wegener glimpsed this need for direct, objective evidence in a paper he published in German in 1927, and which he quotes in his
introduction
to the fourth edition of the
Origin
. ‘For all that,’ he wrote, ‘I believe that the final resolution of the problem can only come from
geophysics.
’ This conviction was to take him to his death.

Alfred Wegener (1880–1930) was the youngest of five children born to Dr Richard Wegener, an evangelical preacher, and his wife, Anna. Two of his siblings died in childhood and the most notable of the three remaining was undoubtedly his brother and fellow scientist, Kurt. The usual facts you hear about Alfred always include that he and Kurt once held the record for the longest balloon ride, 52.5 hours, and that he later wrote a weighty and respected tome on
The Thermodynamics of the Atmosphere
(1912) in which he came up with the still-accepted mechanism of how raindrops form. He also made many arduous expeditions to Greenland, beginning with a two-year expedition in 1906 when he helped map the island’s north-east coast. Crucially, he measured the longitude of Sabine Island and found to his surprise that it appeared to have moved since it had last been measured, about forty years before.

Before the Great War, and shortly after first exposing his heretical drift ideas at a meeting of the Frankfurt Geological Society, Wegener made one more Greenland expedition (1912–13), the first ever to
overwinter on the ice sheet, and to do the journey east to west, using ponies. After the war his father-in-law, Vladimir Köppen, retired as Professor of Meteorology in Hamburg, and Alfred got his first proper job as Köppen’s replacement.

Two more expeditions to Greenland followed in 1920 and 1930 and in between, Wegener became Professor of Meteorology and Geophysics in the University of Graz, moving Else and their three daughters to the city in 1924. The purpose of both Greenland visits was the same – to establish three scientific stations across the widest part of the icecap.

Bad weather afflicted the 1930 expedition, and in late September Wegener led a desperate attempt to take supplies to the remote
central
station. The relief party arrived at the end of October; and after a few days spent sitting out some truly dreadful weather, Wegener and an Inuit companion called Rasmus set off for home. No one saw either of them alive again. The following summer Wegener’s body was found sewn into his sleeping bag and buried in the ice. He is thought to have died of heart failure. What became of Rasmus, nobody knows.

Wegener had a pressing reason for maintaining his interest in Greenland: his great hope of convincing geophysicists by offering a means of direct measurement of the drift phenomenon, escaping the trap of circumstantial evidence and making drift as real and tangible as the planet’s magnetic field.

Wegener reasoned that the best place for seeing measurable drift would be between Greenland and Europe. From the early days he had known about longitude measurements by astronomical methods that had been made by the prestigious Danmark expedition to north-east Greenland in 1906–08, under the leadership of Danish journalist and explorer Ludvig Mylius-Erichsen, who took on the young Wegener as his assistant. Older measurements existed from the general area of
this expedition, so Wegener contacted the expedition’s mapmaker, J. P. Koch, asking if he could compare their expedition’s longitude measurements with them – including measurements taken by the great Irish scientist and explorer Sir Edward Sabine FRS, who went with John Ross’s first Arctic expedition in 1818 and made longitude
determinations
on Sabine Island in 1823. Other measurements not far to the east had also been made, in 1870, by the Germania expedition, and while Koch’s measurements were taken in a different location, they could be connected by triangulation.

By combining astronomical and triangulation methods, Wegener and Koch were able to establish a time-series of longitude
measurements
of Greenland and Europe. These suggested that the gap between them had increased by 4210 metres between 1823 and 1870 (nine metres per year) and by 1190 metres between 1870 and 1907: a massive thirty-two metres per year. The average errors for these
measurements
were, they thought, in the order of 124–256 metres, which was small enough to make the trend believable.

In the last edition of his great book Wegener also referred to the latest longitude determinations made by the Danish Survey, which in 1922 began a series using ‘the far more precise method of radio
telegraphy
time transmissions’; basically, seeing how long it takes a radio signal to travel between transmitter and receiver. These too seemed to suggest that Greenland was moving west, and by about twenty metres per year.

In fact, none of these measurements was actually demonstrating continental drift. The fact that they appeared to – and drift at such break-neck speeds at that – can only be explained today as a
combination
of errors, flukes and perhaps also the unwitting interference of those making the measurements. None of the longitude-fixing
methods
employed at that time was precise enough to detect real drift over periods of tens of years, or even hundreds. But Wegener was not to
know that; and his quest for accurate, direct measurement of the process he was convinced broke up Pangaea and created the
continents
we see today was doomed from the start.

Today you can buy, in minutes and for a few hundred euros or dollars, a navigation system that can pinpoint you or your car
anywhere
in the world, and tell you how to get from Stoke Newington to Paddington without the need for an
A–Z.
To locate your vehicle to within about ten metres it depends on a system of Global Positioning Satellites (GPS), of which there is a constellation of twenty-four. These all occupy known, fixed positions in orbit 20,200 kilometres up, in a system put in space by the US Department of Defense and
completed
in 1994. The system allows you, on the ground, to lock on to objects with very precisely known positions, thus enabling it to
triangulate
on you and pinpoint you precisely. Though GPS was designed and paid for out of military budgets, it was decided to allow its use by civilians after a Korean airliner was shot down in 1983 when it got lost over Soviet territory.

This technology has revolutionized the process of gathering the sorts of information needed to understand the processes of plate motions, all of which require one thing: accurate positioning on the Earth’s surface. The plate-tectonic pioneer Professor Tanya Atwater of the University of California at Santa Barbara has written:

The sort of GPS kit you might buy for your car has the same sort of accuracy as Wegener’s radio-transmission-time method, so you could not use it to detect the widening of the Atlantic reliably over a human lifetime. However, more sophisticated (but still readily
available
) kit can locate a tripod-mounted detector to within, not metres or even centimetres, but millimetres: easily enough to detect the drift of continents over a few years. But by the time war produced this beautiful technological spin-off, the scientific war over Wegener’s theory was long over. The supercontinent of science had re-formed; the resistance of geophysicists, and the opposition of the US
geological
community, had collapsed under the combined weight of evidence provided by geophysics itself.

As Naomi Oreskes of the University of California, San Diego has pointed out in her seminal study of this great scientific revolution, that geophysical evidence was initially no less ‘circumstantial’ than the fossils or the rock types of Suess, Wegener or du Toit. However, that evidence was, still, geophysical in nature. These were ‘proofs’ untainted by association with armchair, qualitative geology; with the opinions of book-learnt experts. They were ‘hi-tech’ at a time when modernity, equated with computers, automation and machines with flashing lights, was extremely compelling – even to the fogies of
traditional
geology.

Geologists who had long been convinced of the reality of drift, and who had had the strength of character to regard its mechanism as a problem for geophysicists to sort out, were gladdened by the
vindication
of their belief. Maybe they were also puzzled that while lack of mechanism had been seen as an ‘objection’ when all the
circumstantial
evidence had been geological, now that the circumstantial evidence was geophysical, nobody seemed to worry about it. But they too were also unable to resist the Zeitgeist, and for the most part
continued
to display that exaggerated and unjustified subservience that
geologists have always tended to show to the Queen of Sciences, despite the fact that they (and not physicists) had been right about the age of the Earth and were now being proved right about drift too.

Geologists had seen it in their sediments and palaeontologists known it in their bones: the Earth had to be hundreds of millions of years old, at least. But the great physicist William Thompson (1824–1907), later Baron Kelvin, had insisted otherwise, assuming that the Earth had cooled from a once-molten mass. What Kelvin didn’t know about was an alternative source of heat: radioactivity. As is often the case with physics, its objections had been quite correct but only according to what was known at the time. There were more things in heaven and earth than were dreamt of by physics at the end of the nineteenth century. Kelvin, it turned out, didn’t know
everything
(a fact confirmed by some of his other infamous prognostications: for example, that there was ‘nothing new’ to be
discovered
in physics, that radio had ‘no future’ and that heavier-than-air flying machines were ‘impossible’).

There is absolutely no doubt that during and after the Second World War the advent of geophysics completely revitalized the Earth sciences. But if, as they sometimes do, geophysicists, especially US ones, write or talk as though physics not only proved the reality of drift but even invented it, those who cleave to the geological tradition smile with the same indulgence old men show towards impetuous tyros, and let it drop in the knowledge that
real
history will teach otherwise.