GOLDILOCKS PLANET
Astronomers call ‘Goldilocks Planets’ the ones that are ‘just right’ for life. Distance from the Sun is not the only control. James Lovelock suggested that life adapted Earth’s environment to suit itself. So despite our having a sun that, like others of its kind, started out faint and grew strong, life conspired to keep our climate equable. Indeed, life changed our atmosphere radically as it evolved from single-celled oceanic creatures to land plants, dinosaurs, and us, introducing oxygen along the way. Asteroids played a role early on, but impacts by large bolides have been rare in the past 500 million years. Even so, they may have changed our atmosphere enough to cause mass extinctions, like that between the Cretaceous and Cenozoic Eras; though the jury is still out and massive eruptions of plateau basalts may have played as important a role.
A blanket of water vapour along with a little methane and CO2 kept Earth’s environment warm by absorbing infrared radiation emitted from the surface. Although three gases make up less than 2% of the atmosphere, they cause much of the warming we experience, so quite small changes have a disproportionately large effect. On geological timescales atmospheric CO2 increases when seafloor spreading is widespread and volcanoes active, and decreases with chemical erosion during mountain building.
The rise of land plants in and after the Devonian complicated matters. Plants feed on CO2 and release it to the atmosphere when they decompose, unless trapped as peat or coal. Controls on CO2 are complicated by whether sea level is low or high. Wobbles in the Earth’s orbit and axis modulate solar radiation on timescales of 20, 40 and 100 thousand years. These interacting controls led to periods when the CO2 in the atmosphere dropped to almost zero and ice became widespread, interleaved with periods where CO2 was abundant and ice was limited or disappeared.
Our climate’s trajectory through time is written in the rocks. When we see in that record evidence for conditions that have no modern analogue we can argue that repeating those conditions may bring similar results. Based on that record, the authors conclude we are now entering the Anthropocene - a period marked by human activity, where further additions of carbon dioxide to the atmosphere may create a climate of little ice and high sea level not seen since the warm periods of the Pliocene or the Eocene. This is a stirring tale, well told; a ‘message in a bottle’. Will we pay attention?
Reviewed by Colin Summerhayes
THE GOLDILOCKS PLANET – THE FOUR BILLION YEAR STORY OF EARTH’S CLIMATE. JAN ZALASIEWICZ & MARK WILLIAMS. Published by Oxford Univ. Press. ISBN 978-0-19-959357-6. 303 pp. List price £16.99
COMPARING GEOLOGICAL AND FOSSIL RECORDS
This book is made up of a collection of different papers tackling the problem of extracting reliable information on biodiversity change from an imperfect geological record. The papers are an eclectic mix, ranging from information-theoretical approaches to in-depth studies, looking in detail at how studies of the fossil records of particular organisms can be applied.
The book begins with an excellent introduction by the editors. There follows a varied mixture of studies in which invertebrates (including microfossils) and vertebrates receive equal attention. The book also boasts wide coverage in time, including material from the whole Phanerozoic.
It is pleasing that a number of supplementary materials have been made available on the Internet, allowing readers to explore topics in more detail. This should be commended also for keeping the cost down! A number of graphs and charts are included with the papers, and these have reproduced very clearly. The use of colour is particularly gratifying in this context, for colour does help considerably with interpretation. However, one does wish that figure 4 on page 148, which should have been reproduced in colour, had indeed been – as this would have made it much easier to use.
The book is an invaluable contribution to this area of study. With the mixture of papers presented it allows a comparison of many different methods and gives a suitable starting point for wider in-depth studies.
The book has a wide potential readership, and I would recommend it to anyone interested in the Earth or life sciences. In an ideal world it would be made available to undergraduates studying any aspects of palaeobiology. It should definitely be found on the bookshelves of all university geoscience departments, as the wide ranging discussion afforded allows for a high degree of integration while also providing a comprehensive ‘snapshot’ of our knowledge and opinions on this complex subject at the present point in time. This book would also be invaluable for developing extension work for students studying ‘A’ level Geology, as the papers are not only clearly set out but readily accessible. Highly recommended.
Reviewed by Gordon Neighbour
COMPARING THE GEOLOGICAL AND FOSSIL RECORDS – IMPLICATIONS FOR BIODIVERSITY STUDIES A J MCGOWAN AND A B SMITH (eds) ISBN: 978–1–86239–336-3 Geological Society Special Publication 358; RRP: £90.00 Fellows’ price: £45.00