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