Born of Ice and Fire
Why do fictional time-travellers so frequently find themselves landing in the Mesozoic, about to be terrorised by dinosaurs? This question, which must have perplexed many palaeontologists, is addressed by author Graham Shields. In a book aimed at graduates and professional geoscientists, he concludes that it is because these creatures’ bipedal and quadrupedal body plans, and the nature of the vegetation they lived among, are familiar to us. But what of, say, the more ancient Snowball Earth, when the world was almost entirely glaciated and the seas were barren of fishes, being a toxic soup but for an oxygenated surface layer? The answer to this, Shields concludes, lies in examining the Precambrian, which stretched from the Earth’s formation to the beginning of the Cambrian Period.
Our understanding of the Precambrian from my 1970s university days has undergone a great revolution in the last 20 years. Hutton’s Uniformitarianism concept, which encourages us to study the modern-day world as a key to understanding the past, cannot be applied to the vastly different Precambrian environments. Instead, we must adopt a more Marxian approach in which we see the present as the product of the past, and therefore follow time’s arrow primarily forwards, not in a mix of forwards and backwards.
Born of Ice and Fire explores how a mostly anoxic ocean loaded with organic matter waxed and waned in response to cycles of bacterial sulphate reduction, which were linked to the weathering of huge salt deposits on land. The book is primarily concerned with such happenings in the Neoproterozoic glacial Tonian (1000-720 Ma) and Cryogenian (720-635 Ma) Periods. The succeeding Ediacaran Period (635-538.8 Ma) is covered in detail and was marked by the origin of large, metazoan life, as exemplified by the fauna found at Mistaken Point, Newfoundland. Those fossils are so precious that palaeontologists have been known to clamber on the cliffs in feet clad only in socks, not hiking boots! For comparative purposes, Shields also delves into earlier and later times, talking, for example, in depth about the Cenozoic’s Miocene Epoch and its last stage, the Messinian (7.25-5.33 Ma). Overall, a reader can gain an understanding of the singular nature of each Precambrian Period.
Born of Ice and Fire is a mixture of thoroughly researched stories about little- and well-known figures in historical geology and at different localities. The book reflects Shields being both widely read and widely travelled.
Reviewed by Brent Wilson
DETAILS
BY: Graham Shields (2023). Yale University Press. 337 pp. (hbk).
ISBN: 9780300242591
PRICE: £20.00 yalebooks.yale.edu
