The Emerald Planet

Title: The Emerald Planet – How Plants Changed Earth’s History

Author: David Beerling

Publisher: Oxford University Press, 2008 (First published 2007)

ISBN: 978-0-19-954814-9

Pages: 216

David Beerling is Professor of Palaeoclimatology at the University of Sheffield. His work on the evolution of life and the physical environment is widely recognized. He has published several research papers and is co-author of Vegetation and the Terrestrial Carbon Cycle: Modelling the First 400 Million Years. This book is also on the related topic of how plants change the history of the earth by influencing components that change climate. Plants are the primary food producers of the planet. Every living being, even carnivores, depend directly or indirectly on plants for their food. Not only food production, these life forms that paint our planet an emerald hue is active in recycling of carbon and water and ultimately is responsible for climate change in subtle ways. The book presents the history of life during the last half-billion years and the triumphs and tribulations it had gone through in this period.

Beerling begins with the most obvious manifestation of plant-hood – green leaves. Even though we take them for granted, leaves evolved rather late in the history of plants. Ever since ancient plants colonized land some 420 million years ago, the most prevalent varieties were leafless forms. This continued for about 40 million years which is a long time even by evolutionary standards. Humans evolved from ape-like ancestors in a tenth of the time! The event which caused the sprouting of leaves and a great flourish of plant life 380 million years ago is claimed to be a decrease in the level of carbon dioxide in atmosphere. Microscopic pores called stomata on leaves through which this gas is absorbed and water is released is dependent on the level of carbon dioxide. If the level is high, number of pores would be less. So, when the level plummeted, pore count shot up, resulting in more leaves. In fact, the spread of plant life was so explosive that it is compared to Cambrian Explosion for the animal kingdom in which marine life forms had a tremendous diffusion across the entire earth. The author stresses a curious fact here. The genetic toolkit for making leaves, like necessary genes were already present in earlier plant forms as well, but the switching on of the gene was prompted by climate change, which was global cooling in this case.

The leafy plants then went through a phase of gigantism. Around 300 million years ago, in the carboniferous era, huge leaves and fens dominated the landscape, complemented with huge life forms like dragon flies that reached 1.5 meters in wingspan and spiders with a length of 1 metre. The reason for the enhanced size is articulated to be a spurt in oxygen levels which rose to as much as 35%, as against 21% at present. The increase in oxygen, coupled with increased atmospheric pressure gifted the faculty of flight to bigger insects too, though with reduced maximum speed. 50 million years later, in the Permian age, oxygen levels suddenly plummeted to 15% which is cited as one of the reasons for the mass extinction of fauna in that era, termed Permian Extinction. True to the requirement that an impartial observer should present all aspects of an argument before the public, Beerling presents ozone depletion as another plausible cause for the obliteration of nearly 95% of all living species virtually overnight. Ozone layer is a shield in the stratosphere which prevents dangerous ultraviolet-B radiation reaching earth. This type of radiation can cause mutation in cells which most often leads to death of the organism. Traces of volcanic eruptions of a massive scale have been observed in Siberia during this time. The resultant gases such as chlorine might have damaged the ozone shield.

Global human population is set to reach 9 billion by 2050. Rice and wheat, the two principal cereals for feeding most of the world has nearly reached their maximum efficiencies. The book presents a unique genetic engineering approach to get over this bottleneck. Rice and wheat uses a special enzyme called Rubisco for photosynthesis which is a remnant of a gene that evolved long back, about 2.5 billion years ago. A carrier molecule containing three carbon atoms act as the mediator and such plants – which means most of them – are called C3 plants. However, in a variety of grasses which include maize and sugarcane, there is a small change in the gene. Here, the intermediary contain four carbon atoms and are called C4 plants. Photosynthesis in C4 plants are much more efficient in converting carbon dioxide to crop. If the genetic photosynthetic pathway of C4 could be transplanted to C3 plants, their yield could be improved still further, ensuring stable food supply to billions in future. However, the popular attitude to GM food need to change for this to materialize.

Beerling presents a strong case for humanity’s attention to focus on anthropogenic global warming due to increase in the level of carbon dioxide. An example of what the world would look like in an atmosphere rich in a mixture of greenhouse gases like carbon dioxide, methane and nitrous oxide was seen 50 million years ago. Subtropical climate prevailed in the poles and the tropics became a hothouse around this time. Fossil remains of forests in the Arctic dated to this period has been recovered. Scientists differ on the reasons that drove the planet through such a hot phase, but the consensus seems to be that the rise in carbon dioxide led to similar increases in other greenhouse gases through complex, interconnected processes. The author’s warning is highly relevant, timely and illuminating.

The chapters in the book are not logically structured, leaving the reader to perform the difficult task of manipulating between incongruent concepts. The author has not been entirely successful to convincingly establish that plants altered the ancient earth’s biosphere. What we glean from the laboured discussion is the opposite idea. The flora and fauna changed or adapted to changes in climate while the unlucky ones unable to cope with simply perished. The book thankfully economizes on the use of botanical nomenclature to the minimum possible, which is to be appreciated from the point of view of a more general audience. A set of monochrome plates are included which is unfortunately irrelevant to the topic under discussion. Figures and charts are cryptic and fail to deliver the message. A hefty Notes section also diminishes the book’s reputation for easy readability.

The book is recommended.

Rating: 2 Star