Supercontinent: Ten Billion Years in the Life of Our Planet by Ted Nield Page B

them was to unlock the tectonic enigma of how supercontinents form and break up. Crucially, mountains were soon to demonstrate the impossibility of up- and-down tectonics and foundered continents.
    In almost his first geological assignment, Suess had discovered evidence of large lateral displacements in the Alps, which seemed to show that massive terrains had been moved sideways for large distances. In doing so he unwittingly planted the seeds of an idea that would unravel not only the structure of mountains but help lead eventually to the idea that continents themselves can move laterally. In later work and his magnum opus Suess did not ignore lateral displacement ; instead he said it was a side effect of ups and downs. For him the basic force governing all tectonics was shrinkage, which caused large sections of the planet’s contracting crust to founder. As he put it, ‘The collapse of the Earth is what we are witnessing.’
    As the Earth’s innards shrank, Suess believed, the crust was put under strain. From time to time parts of it would be forced to subside as the rocky outer shell accommodated to the collapsing planet within. The fragmentation of Gondwanaland, he reasoned, was caused by great subsidences, which left parts of the crust standing high as table-lands (Africa, India and South America) and parts deep below the sea. So the formerly connecting stretches of land in between, for example, Africa and South America, or India and Madagascar, had simply dropped and been lost beneath the waves. Gondwanaland had left fragments behind, but it had not fragmented . The lost parts of it were still there, sunk beneath the Indian and Atlantic oceans like the lost continents of myth. Because these foundered areas of new ocean were broadly elliptical, Suess said, they tended to leave behind landmasses with pointed ends: for the same reason that a round pastry cutter leaves you with triangular offcuts on the rolling board.
    The idea of a shrinking Earth was a powerful one, because it seemed to flow, with all the inevitability of physical law, from the simple observation that it is hot in mines. The further down in the crust you go, the warmer it gets. Heat is escaping from the Earth’s interior. And to nineteenth-century physicists this meant that the Earth was cooling. And if the Earth is cooling, it therefore must be shrinking because that is what happens when things cool. (The idea only finally lost support after the discovery of radioactivity, when scientists realized that, because of the heat generated by radioactive decay, the Earth was not in fact cooling at anything like the rate that had been assumed.)
    Although Suess was still alive when Alfred Wegener first proposed continental drift in 1912, he remained committed to fixed continents that occasionally sank below the waves. Yet his explanations of how the Earth’s contraction could lead to the very lateral displacements that he himself had noted as a young man were never wholly convincing , perhaps even to him.
    Later geologists, Wegener foremost among them, merely tipped their hats at his global observations, synthesis and deductions and, freed from the shackles of contraction theory, explained them away using another mechanism entirely: the notion that continents could move sideways . And that is how, rather paradoxically, Suess is numbered among the true precursors of continental drift, despite having remained resolutely ‘fixist’ all his life.
Everest’s missing feet
     
    What finally killed off the age-old idea of sinking continents was the discovery that continents simply can’t sink: they are, in fact, already floating.
    Gravity is a property of matter. Every object exerts a certaingravitational attraction on every other, but the force is so weak that only truly massive objects exert it to a degree that we can measure. Obviously the Earth and other planets exert gravity, but if you are using very sensitive instruments, even the extra mass of mountains