Geoscientist Online

The Concise Geologic Time Scale

James G Ogg, Gabi Ogg and Felix M Gradstein
Published by: Cambridge University Press
Publication date: 2008
ISBN: 978-0-521-89849-2
List price: £20.00
177 pp

www.cambridge.org

This is the book if you want to know the most up-to-date, accepted and quality-assessed ages of the various geological systems, epochs and stages of the geological column. The errors are becoming so small that there is not much change from the 2004 version with only one amendment over 1myr until we get back to the Carboniferous. There is a useful estimate of the precision, based on the 2004 uncertainties, which shows that for most of the Phanerozoic the precision is <1%, with the base of the Creataceous (145.5Ma) being the worst at nearly 3%. The age results are summarised in a chart using standard colours that are also repeated on a handy, loose plastic pocket table that libraries will wish to secure. Because of the need to fit the tables into a page, some of the stage names appear in minute print (e.g. Gorstian) that makes for really difficult reading.

The value of the book is in the numerous tables rather than the text. Thus the Triassic chapter has tables correlating the ages in Ma with the Primary and Secondary Polarity chrons, the Tethyan and Boreal ammonoid zones and the conodont zones; the Cambrian tables correlate trilobite and conodont zones in South China, Australia, Siberia and Laurentia with numerical ages. The book has a good index, a useful summary of the Standard colours used for the Geological Map of the World back to the early Precambrian, and the agreed International Stage names and Global Boundary Stratotype Sections and Points. If like me, you have no idea which part of the stratigraphical column many of the Stage names relate to, this is a useful list, although with nearly 100 names, such as Guzhangian and Fortunian (both in the Cambrian), many will wonder why we couldn’t have a simpler, more self-evident system, such as O4/5 for the 4th of 5 Ordovician Stages. However, this is not the authors’ fault: they report as they must.

At £20, in hardback, with a really stout long-lasting binding and a plastic wipe-clean cover, on glossy full colour pages, an immense amount of minutely assessed factual information, supplied by innumerable workers, is summarised and clearly and succinctly presented. This is unequivocally recommended. Although research will result in newer versions, this edition will suffice for many for some time to come, if not 1myr!

Bernard Elgey Leake

The Earth After Us: What legacy will humans leave in the rocks?

Jan Zalasiewicz
Published by: Oxford University Press
Publication date: 2008
ISBN: 978-0-19-921497-6
List price: £14.99
251 pp

www.oup.com

This book’s cover shows a modern version of the Sublime, that pleasurable-yet-fearful contemplation of Nature’s majesty and human insignificance that has been a theme of literature since the Romantics. Earth rises against a black sky over the barren surface of the Moon. But something isn’t quite right. The continents have odd shapes, and unfamiliar seas lie between them, even though parts of their coastlines are recognisable. This is Earth in the deep future, whose face plate tectonics has rearranged. From this perspective Jan Zalasiewicz sets out his central theme, which is to enquire what traces of humankind might be discernible 100 million years from now. He invents some shadowy intergalactic explorers to puzzle over the strange anomalies they find in thin strata far down in the rock record, marking the last of six great faunal extinctions.

Presenting this as fiction would have undermined the author’s reasoned speculation. An alien might write A Philosophical Enquiry into the Origins of our Ideas of the Third Planet - but Zalasiewicz cannot speak for aliens. Instead, he rehearses what they would have to learn about Earth if they were to understand our planet in roughly the same way as we do, after 10 human generations of scientific effort. The aliens seem quicker, or perhaps they just live longer. Equipped with the necessary background, they and we can examine human traces. The highest fossilisation potential belongs to coastal cities on subsiding sedimentary basins. Though buildings will be destroyed above ground, the “urban layer” of foundations and cellars tangled with drains, conduits and tunnels is tens of metres thick and will form recognisable strata. Once uplifted these could be mapped along strike for kilometres. The book opens with the discovery of one, in the wall of a deep canyon.

There is much more, on how brick and concrete might “fossilise”, what will happen to plastics, on the imprint of agriculture, the extinction of species and the disappearance of our great rivals in edifice construction – the reef-forming corals. To a discerning eye the human stain will be more subtle and far greater than one spectacular discovery. To an alien eye, almost everything about us will remain obscure. Of why we live, nothing will be discernible, for none of our values, good or bad, will survive. Along with them will go our foods, pleasures, culture and science.

The prospect of such utter disappearance provides a plangent frisson that might be called Sublime, although “projected nostalgia” seems a better phrase. Herein lies the difficulty of taking simultaneous viewpoints - one so deep in future time that all humanity is lost, the other a zestful explanation of human science right now. In the long run we shall all be dead, and so cheerfulness keeps breaking in.

Tim Atkinson, University College London