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The Grand Quadrille,
This review is from: Supercontinent: Ten Billion Years in the Life of Our Planet (Hardcover)
"Did the Earth move for you?", asks the voice beside you. Well, yes. Because that's what it does. All the time. The continent you live on used to be someplace else, and far away from where it is now. Your home ground has even been part of a greater landmass known as a "supercontinent" - and will be again. Hence, the title of this book. Ted Nield provides us with a fine account of how we came to learn about these movements. He has brought together the years of research tracking where the rocks have been and where they are likely to go. He likens the movement of continents to a dance of landforms - a "Grand Quadrille". A fine synopsis of the history of geology and its compelling figures - scholars who had to project what was known in their time back into a distant past.
Earth has been a busy place for the past four billion years, and it hasn't stopped to rest. We speak of the "firmness of the Earth", but that phrase is a sham. The key figure in this story is the great supercontinent of Pangaea that began breaking up 250 million years ago. Assembled from previous continents that had once joined and also separated, Pangaea's breakup into places we live on today have been traced in exquisite detail. The matching of rocks in places separated by wide seas provided the clues. In fact, as Nield relates, it was the vast Atlantic that bears the responsibility for Pangaea's fracturing to form the basis for the continents we know today. The author explains how the continents have been engaging in a Grand Quadrille and will continue to do so - for another five billion years, at least.
The progenitor of the idea of "drifting continents" was Alfred Wegener. Using maps to show how western Eurasia and Africa matched the east coasts of the Western Hemisphere, Wegener proposed they had once been joined, but had pulled apart. He couldn't provide a mechanism for the movement, and his idea was rejected - most notably by the geologic "establishment" of the United States. Rejection of the proposal was so strong there that one British geologist described it as "regarding the Declaration of Independence as retroactive to the Palaeozoic". Continents formed separately and remained so through time, it was thought.
However, one US dissident, Reginald Daly of Harvard, had been in South Africa, encountering the work of Alexander du Toit, who noted similarities in rocks of the Great Karoo and South America. That discovery, enhanced by some detailed measurements in Greenland, suggested that movement was occurring. It took a war and the hunt for submarines to reveal what prompted continental movement. An Irish geophysicist, John Joly had already postulated the mechanism, heat from radioactive elements deep in the Earth required escape. That venting pushed the softer areas in the Earth's crust around. Sitting atop that stirring material, the continents track the flow patterns of the heat.
In moving, the continents encounter each other, joining, fusing and establishing mighty landmasses that break up again. Nield skilfully describes the mechanisms and the people who have read the rocks to understand how they work. Beyond Pangaea, for example, the author cites the work of Mark McMenamin, who proposes a yet older supercontinent, Rodinia. Rodinia's importance in the history of the Earth is that it was probably the extant landform around which complex life, after over 3 billion years, finally emerged. Nield's skill in presenting all these complex ideas and their significance never wanes throughout the book. He's achieved a fine summary of the history of modern geology, supported by a collection of portraits and some line drawings. The emphasis on Pangaea is slightly overdone, but his pointer to Chris Scotese's web page of geologic ages more than overcomes that small limitation. An excellent overview. [stephen a. haines - Ottawa, Canada]