Supercontinent: Ten Billion Years in the Life of Our Planet (3 page)

In other words, oceans can open and close, like a carpenter’s vice,
more than once. Imagine that you open a vice, put the carpenter’s lunch (cold lasagne) into it and squeeze it tight. The lunch will ooze out and up, forming a mountain chain, which we shall call the Lasagnides. You then leave it until the lasagne has gone hard before opening the vice again. By now agents of erosion – mice – have scoured the once mighty Lasagnides back to bench level; but their roots, within the vice itself, remain. If you now reopen the vice to start the process again, some of those old Lasagnide remnants will stick to one jaw and some to the other; but the vice reopens along the same basic line. That is how you get some parts of the same mountain chain in Europe and others in America.

This is the second way to form a supercontinent; one that splits the landmass only to replace the pieces roughly where they were before. Supercontinent theorists call this introversion. Any would-be
modeller
of the next supercontinent faces this crucial question: will the Atlantic go on expanding and become a new ‘world ocean’ through extroversion, or will it eventually, like some tail-eating Leviathan, destroy itself by introversion? Roy sees no reason why the Atlantic should not continue to open; though other ‘preconstructions’ beg to differ, and for them the next supercontinent looks quite different from Novopangaea.

One preconstruction of the next supercontinent, created by Professor Chris Scotese of the University of Texas at Arlington, assumes that the Atlantic will one day close again. I put this idea to Roy Livermore. ‘What Scotese is saying is that subduction is starting up in the Caribbean and the trenches of the Scotia Sea, and that these will propagate.’ It is true; although the western half of the Atlantic Ocean’s floor is welded tight to the eastern seaboards of North and South America, there are some places (in the Caribbean and between South America and Antarctica) where there is subduction. Livermore’s research centres on the Scotia Sea area, however, and he
doesn’t see subduction there propagating up the eastern coast of South America. ‘There is rapid subduction in these places, but it is tending to propagate eastwards,’ he says. In fact, that eastward
propagation
is what makes Drake Passage resemble the pierced armour plating. What has passed between the two headlands is a narrow slice of ocean floor.  

‘Plus, it’s still a moot point in geophysics as to how you start
subduction
off. How you do this at a passive margin, where the ocean crust is welded to the continent edge, is really not clear. Around the Pacific you already have well-established subduction zones that have been going on since the Permian. Why would they turn off ?’  

Livermore shifts his attention to the preconstruction he made for 100 million years hence, halfway to Novopangaea. ‘To show how
continents
can rift,’ he says, ‘I have taken the liberty of opening up a new rift in here …’ and his pen follows a new seaway connecting the Indian Ocean with the North Atlantic. ‘We know the East African Rift is active, so we propagate that into the future by opening a small ocean. East Africa and Madagascar have moved across the Indian Ocean to collide with Asia; Australia has already collided with South-East Asia.’ South of what is now India a mountain chain has arisen along a new subduction zone. And just south of it lies a familiar
landmass
, in an unfamiliar position. It is Antarctica. ‘I don’t believe Antarctica is going to stay at the pole,’ he says. ‘I
want
it to come north. Every other fragment of Gondwana has done that, piece by piece, and in the future Antarctica will; but only if it’s dragged north by a subduction zone.’

Meanwhile the Pacific continues to shrink. North America and South America begin to wrap around the coasts of Asia. Australia has already collided with Japan and stuck. North America collides first, and South America sweeps around to consume the last vestiges of the Pacific and finally form Novopangaea.

Livermore is only the latest of a number of distinguished geologists to speculate about how today’s continents might eventually
recombine
. The first to do so was Paul Hoffman. He called his future supercontinent, an amalgam of America and Asia, Amasia.

Much has been written about Paul Hoffman, and such accounts usually begin by remarking that he was the first on the scene. Writer and palaeontologist Richard Fortey has written: ‘If expertise is defined as knowing more and more about less and less, I am at a loss to describe what it is to know more and more about more and more, but that is the Hoffman condition.’

One of the leading geologists of our age, Paul Hoffman is a man of whom stories are told. With his tanned, ascetic head, flashing eyes, mane of white hair and flailing, wiry arms, he has never been known to take prisoners. One geologist who has worked with him put it to me succinctly when he said, with a smile and a shake of the head: ‘Paul is one hell of a scary dude.’

Hoffman is now Sturgis Hooper Professor of Earth Sciences at Harvard University. Much of his career, however, was spent at the Geological Survey of Canada. As one of the foremost thinkers on how plate-tectonic processes form supercontinents, and on how it might be possible to reconstruct supercontinents before Pangaea, Hoffman was also the first to write about the supercontinents of the future.

He, like Roy Livermore, thought that the Atlantic could well
continue
to expand and that we might be now in the middle of a process of continental extroversion (turning Pangaea inside out). He
presented
his idea at the 1992 Spring Meeting of the Geological Society of America in Montreal. ‘The Americas are swinging clockwise about a pivot in NE Siberia,’ he wrote in his abstract. ‘They seem destined to fuse with the eastern margin of a coalesced Africa+Eurasia+Australasia, instituting the future supercontinent “Amasia”.’

Hoffman used this pioneering preconstruction as a means of
explaining
something he believed about how supercontinents had formed and broken up in the deep past: the process of extroversion, turning old supercontinents inside out. He never published a map of Amasia, though in essence it might have looked something like Livermore’s Novopangaea. However, he did give it a name, and a good one.

Amasia is often referred to by Earth scientists as shorthand for an extroverted resolution to the current pattern of Pangaea’s break-up; but the concept received relatively little media coverage and so never really escaped into the wider world. Not so, however, Chris Scotese’s projection, based on the opposite assumption, that the Atlantic will one day close back on itself. This creature definitely got out. And like all supercontinents whose names run amok, it has attracted the
attentions
of some strange and mystical colonizers.

Pangea Ultima’s creator, Professor Chris Scotese, is a bear of a man with a big beard and a big smile. He has been involved for much of his career in reconstructing the continental positions in the past – a subject called palaeogeographic reconstruction – and in the Paleomap Project, an amiable, eccentric, homespun (and award-
winning
) website,
www.scotese.com.

Scotese has produced a series of palaeogeographic atlases since he was an undergraduate at the University of Illinois in Chicago. His first were published as miniature ‘flip books’ in the 1970s and computer
animations
in the 1970s and 1980s. While a graduate student in the University of Chicago and the Paleomagnetic Laboratory at the University of Michigan, he and his supervisors published a series of maps that uniquely combined plate tectonics, palaeomagnetism and palaeogeography. These early publications of the Paleogeographic Atlas Project were the first to illustrate, through the emerging
understanding
of plate tectonics, how ocean basins and continents have evolved over the past 542 million years of Earth history.

Scotese’s work did not hit the media, however, until 2000, when the NASA publicity machine published an interview with him about his work on the Paleomap Project. Attention focused on his ideas about the next supercontinent.

‘We don’t really know the future, obviously,’ he told NASA science writer Patrick Barry at the time.

Among those predictions: Africa is likely to continue its northern migration, pinching the Mediterranean closed and driving up a Himalayan-scale mountain range in southern Europe. Of that
everyone
seems certain. Australia is also likely to merge with the Eurasian continent. ‘Australia is moving north, and is already colliding with the southern islands of South-East Asia. If we project that motion, the left shoulder of Australia gets caught, and then Australia rotates and collides against Borneo and south China – much as India did 50
million
years ago – and gets added to Asia.’

So far Scotese’s vision works out very similar to Livermore’s and Hoffman’s. But his Pangea Ultima forms differently from Amasia or Novopangaea. Scotese believes subduction will start up on the west side of the Atlantic. The Mid-Atlantic Ridge is then eventually pulled into the Earth. The widening stops and the Atlantic begins to shrink.

Late Permian, 258 Ma

Paleogeographic maps by C. R. Scotese, PALEOMAP Project, University of Texas at Arlington (www.scotese.com)

 

Eocene, 50 Ma

 

Scotese told reporters in 2000: ‘Tens of millions of years later, the Americas would come smashing into the merged Euro-African
continent
, pushing up a new ridge of Himalaya-like mountains along the boundary. At that point, most of the world’s landmass would be joined.’ The result, however, is very different from Hoffman’s Amasia or Livermore’s Novopangaea. It looks like what it is: Pangaea reformed.

Modern World

Late Permian, Eocene and today’s world maps, showing the break-up of Pangaea according to modern research. © 2002, C. R. Scotese, Paleomap Project.

As a result of the news coverage generated by the NASA story, the name Pangea Ultima is now out there in the wider world in a way that Amasia never was. But there is something slightly wrong with its name. Scotese has called it ‘ultima’ because, as his website proclaims, ‘it will be the last supercontinent to form’. But in reality the
next
supercontinent
is just that. Whether Pangea Ultima, Amasia or Novopangaea, the next supercontinent will break up in turn and many other
supercontinents
will form again before the Earth is destroyed. Perhaps a better name might have been Pangaea Proxima.