permaculture

["Lawrence F. London, Jr." <lfl@intrex.net>]

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Books and Arts

Nature 447, 778-779 (14 June 2007) | doi:10.1038/447778a; Published online
13 June 2007
Secret life of plants
Paul Falkowski

BOOK REVIEWED-The Emerald Planet: How Plants Changed Earth's History
by David Beerling

Oxford University Press: 2007. 304 pp. £14.99

Plants are an inextricable part of the human experience. They provide us
with food and fibre, drugs and building materials, fuel and fodder,
fragrances and shelter. Although we are literally beholden to plants for our
very existence, the geological history of plants and their role in
transforming Earth's biology and chemistry is a largely unsung tale.

This book tries to capture the stories for a scientifically literate reader.
It is not written, nor intended to be, a popular science blockbuster, but
rather an accessible monograph, in the modern sense, that examines basic
questions that palaeobiologists and geochemists have addressed for decades.
When did oxygen-producing organisms evolve? How did they come from the
oceans to invade land? Once on land, how did they transform the rocky world
in which they found themselves to create soils and environments conducive to
terrestrial animals, such as ourselves?

The author, David Beerling, trained in palaeobiology and geochemistry, tells
two stories in parallel. One is the history of Earth and how photosynthetic
organisms transformed it. The other is the history of humans who sought to
understand Earth's history. Both are eloquently and engagingly merged in a
scholarly, yet generally accessible book that bespeaks of the author's love
for plants, the geological history of Earth and the history of science.

Traditionally, Earth's biological history has been inferred from fossils.
The fossil record of plants extends back to about 420 million years, yet the
fossil record of animals is at least 200 million years older, and fossils of
marine microorganisms extend back several billion years (although the
validity of some of the earliest microfossils has been questioned). So when
did oxygen-producing organisms first appear on Earth?

We are not certain; molecular fossils (organic remnants of organisms that
are physically lost in the fossil record) suggest that the earliest
oxygen-producing microbes — cyanobacteria — evolved about 3 billion years
ago. Over the past 50 years, geochemists, armed with mass spectrometers and
other sophisticated instruments, have been able to piece together isotopic
records of carbon and sulphur, from which the oxidation state of Earth can
be inferred. These records suggest that the atmosphere of our planet
'flipped' from a mildly reducing, anaerobic condition to a mildly oxidizing,
low-oxygen state about 2.3 billion years ago. Subsequently, cyanobacteria
responsible for the generation of oxygen were appropriated via a series of
symbiotic associations, and spread throughout the oceans as eukaryotic
algae.


Books and Arts

Nature 447, 777-778 (14 June 2007) | doi:10.1038/447777a; Published online
13 June 2007
Dirt cheap soil
Eric A. Davidson

BOOK REVIEWED - Dirt: The Erosion of Civilizations
by David R. Montgomery

University of California Press: 2007. 295 pp. $24.95, £15.95

If everyday expressions offer clues to what we value, then the common use of
'dirt-cheap' to describe anything inexpensive speaks poorly of our
appreciation for soil. Like water andair, soil is not efficiently traded and
priced in the marketplace, and yet we could not live without it. It doesn't
take a rocket scientist to figure out that food security and human
well-being depend on fertile soil. That expression implies admiration for
the intelligence of rocket scientists, and similar praise is due to Earth
scientist David Montgomery, whose new book insightfully chronicles the rise
of agricultural technology and the concomitant fall of soil depth just about
everywhere in the world, from prehistoric to modern times. The topic could
not be more timely, as recent large-scale expansion of maize (corn) in the
United States and sugar cane in Brazil for biofuel production signals a new
era of competition between the energy and food sectors for the globally
finite resource of arable land and the remaining good soil.

Montgomery catalogues a tragically recurrent pattern. Starting with the
first farmers in the Tigris and Euphrates River basins, across the
Mediterranean of the ancient Greeks and Romans, through bronze, iron and
industrial ages, repeated in the Americas and in Asia, and up to
contemporary practices on industrial mega-farms and smallholder
slash-and-burn fields. In each case, agriculture expanded on good land,
which fuelled population growth, followed by further agricultural expansion
onto marginal land, ultimately leading to soil erosion, declines in
agricultural productivity, and often societal collapse and emigration.