Easter Islanders, aware that they were almost completely isolated
from the rest of the world, must surely have realized that their
very existence depended on the limited resources of a small
island. After all, it was small enough for them to walk round
the entire island in a day or so and see for themselves what
was happening to the forests. Yet they were unable to devise
a system that allowed them to find the right balance with the
paraphrase Ponting, we are aware that Earth is completely isolated
from the rest of the universe and we realize that our very existence
depends on the limited resources of this one small planet. After
all, it is small enough for us to fly around in a day or so
and see for ourselves what is happening to the forests (and
plains and waters). Yet we seem unable to devise a system that
allows us to find the right balance with the ecosphere."
- Peter Miller and William Rees 2
INSERT SHORT PARAGRAPH ABOUT EASTER ISLAND
live on a planet with finite resources, with only one input from
the outside -- the energy from the sun. While our technologies can
rearrange matter to better suit our convenience, and extract energy
by reaching farther and farther into the depths of the Earth, the
limits to this process have become evident. A return to "ecological
thinking" is necessary if we are to survive. Our deep involvement
and preoccupation with technological thinking to the exclusion
of ecological thinking has been a major contributor to environmental
this unit, we look at ecology -- the understanding of living systems
in relation to their environment. Ecology is the study of the patterns
and relationships of these systems. In Greek, the word "oikos"
means "house," and "logos" means "pattern."
The word "oecologie" was coined by Ernest Haeckel, German
scientist and follower of Darwin, in 1866. From that time and throughout
the 1890s European botanists studied systems of plants and land
and their interdependencies, giving rise to the science of ecology.
Thus the science of ecology has always had a holistic approach to
nature, connecting communities and systems. The philosophical roots
of ecology and the land ethic of Aldo Leopold are discussed in detail
in the unit on Ethical Systems.
early study of ecology was tilted towards moral philosophy. As a
science, it grew in parallel, more as a description of the distribution
of plant communities, and their patterns of succession. In the 1920s
and '30s ecology became more of a discipline of science. In 1927,
Charles Elton, a colleague of Aldo Leopold, coined phrases such
as "food chain" and "niche" and began to work
on the way nutrition started with the sun, and on the natural dependencies
of organisms and "communities of plants." The English
ecologist Arthur Tansley proposed the term "ecosystem"
for the total system of relationships.
comparison of ecological thinking with technological thinking is
important to our understanding of why conventional technologies
have worked with little regard for the environment, except as a
source of raw material or a place to dump -- or even as conditions
and constraints to conquer. Table 1 contrasts features of conventional
technological thinking with those of ecological or systems thinking.
on parts and how they connect for immediate performance
on patterns, context, connectedness, and relationships
reduced or taken apart for understanding
= sum of parts
understanding of parts in context of larger whole
> sum of parts
as collection of objects; relationships secondary.
are networks of relationships
sense of rigid structures of domination and control
order of interdependence
oriented thinking, often in terms of closed systems
thinking or weaving together to make sure there is free
flow in network; structure follows.
1: Technological Thinking vs. Ecological Thinking (adapted
from FRITJOF CAPRA).
is the result of human effort to transcend limits placed on us by
space and time. Population explosion has made us aware that the
extent to which we can overcome space constraints is limited.
and efficiency are the main metrics of success in technology, which
has led to a lack of appreciation of time -- that it takes time
to build the complex intricate system that houses and nurtures us
as part of it. This lack of respect for time that is embedded in
our technological thinking has been one of the most salient factors
in degrading environmental quality. To feed our technological ways
of life, we currently destroy 24.7 million acres of ancient forest,
pump 6.6 billion metric tons of CO2 into the air, and
pump 24.9 billion barrels of oil out of the Earth each year.3,
have typically focused only on narrow segments of the entire system
to which the specific technology relates. For example, the design
and marketing of the automobile had no forethought about the disruptions
large numbers of automobiles would have on land, on air, on energy
use, on social units such as cities and families, on all aspects
of our ways of life. Technological thinking has traditionally had
characteristics that are contrary to holistic, systems thinking
-- but this has slowly begun to change. The emerging practice of
industrial ecology looks at products as part of a larger cycle and
attempts to reduce the environmental impacts of production, consumption,
has traditionally dealt only with natural systems. The new field
of industrial ecology is beginning to study industrial behavior
and biogeochemical cycles as a part of a system, using the results
to design environmentally friendly products and processes. For true
integration, however, we need to merge the two ecological systems
-- natural and industrial -- with the right consideration of space
and time. We are still a long way off from this undertaking!
sensitivity and response of various organisms to nature's cues is
beautifully illustrated in a flower clock designed in 1751 by Carl
von Linnaeus, who is considered the father of botany. Noticing that
different flower species opened during different times of the day,
Linnaeus designed a clock (Figure 1) using the characteristic time
of opening and closing of the flowers. He found that once bees had
found the flowers they preferred, they would return to the "clock"
at the appropriate time, rain or shine! This is a beautiful example
of the temporal behavior deeply embedded in the ecological system,
including animal physiology. It has also been shown through experiments
that certain medications or treatments for human illnesses are more
effective at different times of the day (for reasons not fully understood
by science). Technology has often tended to ignore these time-linked
behaviors and effects.
1: Representation of the flower clock proposd by Linnaeus.
The 12 hours
of the clock run from 6 a.m. to 6 p.m.. Click
for larger image.
Source: The Clocks That Time Us, by Moore-Ede, Sulzman,
and Fuller. 6
Ponting, Clive. Green History of the World, Oxford University
Press, 1991. p. 7
Miller, Peter and William Rees. Ecological Integrity: Integrating
Environment, Conservation, and Health. (Edited by D. Pimentel,
L. Westra, and R.F. Noss). Island Press, 2000. p. 3
Source: Greenpeace Video, Magnificent 7. Greenpeace USA Media
Global CO2 Emissions from fossil-fuel burning, cement
manufacture, and gas flaring in 1998, as measured by weight of carbon.
Source: Carbon Dioxide Information Analysis Center, http://cdiac.esd.ornl.gov/ftp/ndp030/global98.ems.
Global Crude Oil Production, 2001. Source: Energy Information Agency,
Moore-Ede, M.C., F.M. Sulzman, and C.A. Fuller. The Clocks That
Time Us, Harvard University Press, 1982. p. 12
the mid-eighteenth century, the Swedish botanist Carolus von Linné
(1707-1778) better known as Linnaeus, invented the classification
scheme of the living world that we still use. Early scholars such
as Aristotle and Pliny had also invented such classifications, some
of which still hold. For example, Aristotle first classified dolphins
as mammals! Pliny (23-79 AD) wrote a 37-volume Natural History,
classifying all reported living beings! Linnaeus' scheme gave every
living being two names. The first is its genus, the group
to which it belongs, and the second the species, describing
the subclass in the genus. Thus the present species of humans are
Homo sapiens, others like Homo erectus and Homo
habitis being extinct. The genus and species have Latin names,
with the genus term written capitalized.
members of the same species in a particular area at the same time
constitute a population, and the area is called the habitat
of the species. Different species may live together in a habitat,
forming a community. The different species in a community
might interact through a food web or exist in symbiosis. Symbiosis
is a state in which members of different species live in physical
contact, mutually benefiting from each other's presence. Lichens
that occur on exposed rocks throughout the world are a wonderful
example of symbiosis: They are usually a fungus and an algae (or
bacterium) living symbiotically. The photosynthetic algae provide
nutrients for the fungus. The fungus seems to provide support and
the ability to extract essential minerals from the rock. Because
of this pairing, lichens can colonize extreme environments where
the fungi or algae alone cannot exist. These include the rocks of
Antarctica and of Donegal, Ireland. The lichens scraped off from
rocks in Donegal is used to color the woolen material called Donegal
are the several habitats that co-exist in a particular climatic
area. Tropical rainforests and coniferous forests are examples of
biomes. Biosphere is the general term for the highest organizational
level in which life exists, ranging from the very depths of the
oceans to several thousand meters into the tropospheric region of
the atmosphere, and including land masses.
and Ecological Balance
are living and nonliving components of an area that include the
habitat and the physical and chemical environment. The classic definition
of an ecosystem was stated in 1953 by Odum: any unit that includes
all organisms (i.e., community) in a given area interacting with
the physical environment so that a flow of energy leads to a clearly
defined structure, biotic diversity, and materials cycles. [INDIRA
- I don't have a reference for this, because it came from Sharon's
modules. Should we just take it out?]
do we mean by "ecological balance," "balance of nature,"
or "ecosystem stability"? Balance and stability in this
context are different from a static condition in which there is
no change. Nature is continuously changing, and especially over
periods of thousands of years, changes substantially. In his book,
Discordant Harmonies, Daniel Botkin writes, "...every
thousand years a substantial change occurred in the vegetation of
the forest, reflecting in part changes in the climate and in part
the arrival of species that had been driven south during the ice
age and were slowly returning."2
The forest he is referring to is in the western region of northern
Minnesota and southern Ontario, which Botkin studied in detail.
this difficulty of defining balance, and the fact that balance or
stability occurs over different time scales, ecologists talk of
"ecological stability" or "resilience." For
each of these terms, one may focus on one or two species and their
change over time. Most ecologists study population ecology or community
ecology. In general, the stability of 10 to 100 species over time
scales of 10 to 1000 years is considered when talking of stability.
Over this time, populations may remain in an equilibrium. Population
resilience is defined as the rate at which the population return
to equilibrium after it is disturbed.
1A-D show a representation of the progress of the Earth's ecosystems
as we progress from prehistoric times, through hunter-gatherer societies
and agricultural societies, to an ecosystem in which industrial
activities dominate. In Figure 1A, the different levels of the ecosystem
depend upon the plants, the primary producers of nutrients from
H2O and CO2 using the sun's energy. As we
go from 1A to 1D the role and impact of humans increase. In Figure
1D, human industrial activity and pollution dominate. As the human-dominated
fraction of the system increases, we see the shrinking of the other
levels, representing loss in biodiversity and even species extinction.3
1A: Trophic levels in an ecosystem.
1B: Ecology of a hunting-gathering economy.
1C: Ecology of an agricultural economy.
1D: Ecology of an industrial economy.
Clark, Mary E. Ariadne's Thread. St. Martin's Press,
New York, 1989. Reprinted with permission of Macmillan Ltd..
Johnjoe. Quantum Evolution, Norton: New York, 2000.
Botkin, Daniel. Discordant Harmonies, Oxford University Press:
New York, 1990. p. 62
Clark, Mary E.. Ariadne's Thread, St. Martin's Press: New
or biological diversity, is generally defined as "the variety
of life and its processes," and can be thought of as the full
richness of life that exists on Earth. The term "biodiversity"
can be applied on several scales. We often talk of the biodiversity
of an ecological or climatic region, such as the biodiversity of
the Arctic region, of tropical rainforests, of coastal regions,
or of plains and prairies.
a smaller scale, we sometimes talk of genetic biodiversity within
a given species, or even a local population of a species. For example,
even before the current biotechnology upsurge, genetic manipulation
of plants by horticulture significantly decreased biodiversity in
the world's corn crops. Species of corn were selected to be propagated
specially for their desirable characteristics, such as amount of
crop yield or low susceptibility to certain pests. Such "monocultures,"
however, are then all susceptible to the same diseases or pests.
Monocultures have very little genetic diversity to ensure resilience
of at least some of the species to certain stresses. This can lead
to destruction of large corn crops all at once. Continued genetic
engineering by large agricultural corporations will only exacerbate
corn example is a good illustration of the fact that a species or
ecosystem can exist on a very large scale but not exhibit biodiversity.
Another similar example is the cultivation of plantations of genetically
identical pine trees that are replacing the forests of the south.
E.O. Wilson, a Pulitzer Prize-winning biologist at Harvard, estimates
that a pine plantation has 90 to 95% fewer species than the natural
forest it replaces.1
richness also varies from place to place depending on the energy
available for different species to share and the stability of climate.
Solar energy and water availability are of course the most important
factors for biodiversity. This is why tropical forest have the most
viable ecosystem therefore must have:
A source of energy
A supply of raw materials
for storing and recycling the necessary materials
that allow it to evolve at suitable rates
general, biodiversity of a given ecosystem consists of three components:
composition, structure, and function. The composition of
an ecosystem includes the groups of organisms, species and the various
organic and inorganic substances that are inputs and residues of
the organisms. An ecosystem has two primary types of structures:
architectural structure, consisting of spatial organization and
patterns; and social structure, which includes the interdependence
and relationships among the parts. Organisms, materials, and energy
of the ecosystem function in relation to one another. They
might interact to influence processes in the ecosystem or the structure
of the ecosystem.
importance of biodiversity stems from the fact that ecosystems evolved
over thousands, hundreds of thousands, or even millions of years,
and are therefore in delicate balance, with each species playing
a vital role. Appreciation of biodiversity has come about as a result
of an increased understanding of the interrelatedness of species
in a given habitat.
of the importance of biodiversity represents a paradigm shift for
conservationists. Within a biologically diverse community, each
species -- no matter how small -- plays an important role in the
ecosystem. Historically, humans have been moved to conserve and
protect that which is beautiful and inspiring, and meets our narrow
definition of "importance." To maintain biodiversity,
it is necessary to protect species that we may not find beautiful,
and some that may be barely visible.
are varying ideas about how and what biodiversity must be protected
or conserved in nature. As seen above, biodiversity as a whole includes
soil fertility, water quality, and air pollution levels in addition
to species diversity. So these qualities are as important as endangered
species in understanding and maintaining biodiversity. Preserving
these is central to the stability of an ecosystem. The three different
types of stability that need to be preserved are: species stability,
structural stability, and process stability. These three very general
factors are in somewhat of a hierarchical relationship. Process
(including inputs and ways to overcome shocks) interacts with structures
to preserve species. But disturbing the species balance will affect
the other two, so that this once again demonstrates the close interdependence
of the components of this system - the ecosystem.
Name any animal populations that have become extinct in
stability is not a static property, but a dynamic balance. The two
qualities (or properties) which characterize ecosystem stability
are resistance and resilience. Resistance represents the potential
that prevents tree and animal populations from succumbing to stresses
such as drought or high pollution. Resilience is the capability
that comes into play when organisms are weakened or killed. It is
defined as the rate at which population density in an ecosystem
returns to equilibrium after it has been disturbed away from equilibrium.
Alternatively, it could be defined as how large a range of conditions
a system can tolerate and still remain in equilibrium. Resistance
and resilience depend on a variety of factors, each important on
different temporal and spatial scales.
the fact that typically there are a variety of species in an ecosystem,
shows that natural evolution results in subtly complex systems that
best preserve local habitats -- systems that can hardly be designed
and engineered by human technologies. Local ecosystem change and
undergo modifications through time. Certain niches became modified
in time and space through small and large disturbances. Some species
extinction may even be "natural." It is the rate at which
technology induced change, or anthropogenic change in general, happens
that might disturb an ecosystem beyond its own capacity to repair.
among organisms maintain diversity and in destroying or enhancing
one species in a local ecosystem may destroy the whole system in
time. While grazing elk normally reduce shrub dominance and promote
diversity in early successional forest of the western United States,
some of this same region now has had its biodiversity significantly
reduced by overgrazing cattle. This type of phenomenon, "overgrazing"
for example, occurs when humans intervene to pus the system out
and Indicator Species
There are certain species whose role in maintaining the balance
of an ecosystem is so significant that they are known as the "keystone
species." A keystone is the stone at the summit of an arch
that supports all the other stones and keeps the entire arch from
collapsing. Therefore, the keystone species in an ecosystem is a
species that supports many other species in that ecosystem. The
removal of the keystone species would result in quick and noticeable
change or degradation of an ecosystem.
sea otter has been referred to as a keystone species in western
Alaskan coastal ecosystems by the US
Department of the Interior and the US Geological Survey.
Because of a decline in the population of Steller sea lions and
harbor seals in Alaskan waters, killer whales have been feeding
on sea otters. The sea otter is considered keystone because it feeds
on sea urchins, who in turn feed on kelp. Without the sea otter,
sea urchin populations would rise, leading to probable destruction
of the kelp forests, disrupting large portions of that coastal community.
Without the otters to keep the sea urchin population in check, the
habitat of the entire community would be altered significantly.
the designation of keystone species is sometimes controversial.
For example, it could be argued in this case that since it was actually
the decline in population of Steller sea lions and harbor seals
that caused killer whales to feed on sea otters, the sea lions or
seals are also a sort of keystone species. This case demonstrates
that large disruptions in ecosystems can often be traced back even
farther than disruptions in populations of the so-called keystone
species, again underscoring the strongly interrelated nature of
keystone species are those that play a role in the ecosystem
that is much larger than their total number or biomass suggests.
Their interaction and rate of consumption determines the tolerance
of the system in an important way. Thus the sea otter is considered
the keystone species in this chain because they consume sea urchins
in large enough quantities and at a fast enough rate so that the
relatively slow-growing kelp can keep up with its consumption by
species are species whose changes in behavior -- or more often,
population -- alert us to environmental conditions that threaten
ecological niches, or even the entire global system. These species
serve as the "canaries in the coal mine," warning us that
levels of something in the environment are increasing or decreasing
beyond the resilience of the system.
scientists today believe that the hundreds of species of amphibians
on the decline globally are indicator species, warning us of how
human impacts on the climate and air/water quality are having cumulative
effects. For more information on this topic, see Tracking the Vanishing
Frogs, by Kathryn Phillips.
management, including forest management, is often chosen as a way
of maintaining biodiversity. In certain cases, land (including forests)
is managed by reducing diversity to maintain what is required for
some economic crop, such as the earlier mentioned pine plantations
of the south for paper and wood. This reduction of biodiversity
eliminates habitat and sets in place a system that requires continuous
maintenance. When laws and forest are managed to preserve natural
diversity, the existing structures and processes have to be studied
in some detail for a significant amount of time. Even then, "managing"
always implies interfering with what would have occurred naturally.
an amount of work has gone into understanding the forces that create
and maintain biodiversity. Any management looks at habitat closely.
Trees and shrubs provide the primarily habitats for animals as well
as other plants and microbes. Biodiversity is also believed to play
an important role in stabilizing an ecosystem against stress, such
as climate fluctuations and pest outbreaks. So even in forest managed
for an economic product, managers are beginning to work to preserve
diversity. However, the complexity and the dependencies are never
completely understood, and the disruptions caused often destabilize
to biodiversity are as numerous and varied as the sum of problems
that face the overall environment. Symptoms of severe stress in
ecosystems have been noted all over the world. Following are several
main categories of threats to biodiversity. It is important to note
that, although we've grouped the threats into several main categories
below, almost all threats facing ecosystems today are the result
of human and industrial activity.
the human population increases, and we use up more and more land
area for residences, industry, and commercial or recreational activity,
habitat loss becomes a greater threat to biodiversity. Species are
forced to live in higher concentration, or move into habitats to
which they are not adapted.
often also bring with them exotic or invasive species -- species
that are not native to a region or habitat. These invasive species
sometimes carry with them viruses or disease to which the local
population is not adapted, causing a direct harmful effect. The
exotic species present competition for food and habitat, and sometimes
"edge out" native species due to their pervasiveness.
we mentioned before, there is a high level of interdependency among
species in an ecosystem, and a reduction of population or loss of
one species often leads to population changes among other species.
An ecosystem, once altered, can take years to return to a state
of equilibrium after a disturbance.
environmental problems -- like air pollution, ozone depletion, and
global climate change -- are also often serious dangers to the survival
of threatened species. Tracking
the Vanishing Frogs, by Kathryn Phillips, documents the
research of scientists into the disappearance of many populations
and species of amphibians. Scientists are more and more convinced
that many of these disappearances are related to increased UV exposure
(due to the thinning of the ozone layer) or seemingly slight changes
in weather and precipitation patterns that affect the frogs' reproductive
behavior.2 Within the last twenty
years, 5100 amphibian species (including 2300 frog and toad species)
have disappeared. As we mentioned earlier, amphibians are considered
by many scientists to be an indicator species for damage from ozone
depletion or global climate change. We say that this is an indicator
of global, rather than local, change because amphibians in totally
unrelated niches are disappearing concurrently!
to trees from industrial pollution in Germany provide another example
of ecosystem stress due to environmental problems. In 1982, the
former West Germany noted that 8% of its forests showed decline.
In 1983 it was 34% and by 1985, 50%! Dying of forests from pollution
has become a sever problem Acid precipitation, causing an imbalance
in soil chemistry, has been identified as the reason in Germany
and in the Great Smokies Nature Park in the U. S.. Pollution is
believed to have stressed the ponderosa pines in the San Bernardino
National Forest of California so that they could not produce then
natural digestive chemicals. This made them susceptible to bark
beetles. Trees can also get overpowered by fungi that cause root
rot when they are stressed.
causes of soil degradation are deforestation, over-exploitation,
overgrazing, industrialization, and large-scale agricultural activities
maintained through artificial fertilizers. This leads to loss of
natural cycles - decay of organic matter, nitrogen fixation, etc.
- and decline in soil fertility. Soil fertility in Wyoming, Panama,
Thailand and other regions have been destroyed by clear cutting
forests which lead to loss of topsoil and of soil compaction that
are different types of losses of species as follows:
of a once common species - the population of a species is
greatly reduced, but the habitat still exists and the species
could be replaced though there is still some loss of variety in
the gene pool.
from a wildlife refuge in Nebraska being reintroduced
to Theodore Roosevelt National Park in North Dakota. (1956)
Photo courtesy of the NPS.
Buffalo on the American plains, whose population faced near extinction
due to large-scale slaughter... Buffalo populations were tremendously
reduced, to near extinction, the end of the 19th century. Buffalo
were slaughtered for reasons of commerce, sport, and even political
reasons. It was the policy of the U.S. Military (in practice,
if not officially) to kill as many buffalo as possible. "In
1874, Secretary of the Interior Delano testified before Congress,
'The buffalo are disappearing rapidly, but not faster than I desire.
I regard the destruction of such game as Indians subsist upon
as facilitating the policy of the Government, of destroying their
hunting habits, coercing them on reservations, and compelling
them to begin to adopt the habits of civilization.'"3
or global species extinction -
the species is gone (either from its habitat or from the Earth)
forever and all current and potential adaptations are lost. Species
extinction has regularly occurred since the beginning of life
on Earth. Historically, losses occurred at a slow enough rate
that ecosystems to adapt; however, losses due to human activity
are happening at a much higher rate, causing concern among
scientists and conservationists.
Example: Deforestation...The rate of extinction due to deforestation
is now 10,000 times that before human civilization.
FROM STUDENTS OF SPECIES LOST SINCE 1980'S>>
two animals from your state on the endangered species
disruption - this is the most serious of the three because
it is not just the loss of several species, but of an entire ecosystem.
Example: Three Gorges Dam... ecosystem
loss that will result from the construction of the Three Gorges
Dam in China. This is a project whose goal is to build the world's
largest hydroelectric dam on the Yangtze River, creating a 400-mile
long reservoir and displacing up to 1.9 million people -- threatening
the entire ecosystem.4
Ideally all of our environmental regulations and policies protect
ecology by preventing pollutants from degrading the habitats of
species. However, in the USA there is one federal regulation that
specifically discusses species protection: the Endangered Species
enacted in 1973 to place the highest priority on the protection
It is administered by the US Fish and Wildlife Service, the National
Marine Fisheries Service.
ESA prohibits government agencies from authorizing, funding, or
carrying out any activities that might harm an endangered species,
or its habitat, and prohibits individuals from taking an endangered
species (taking can be broadly defined as causing any harm) without
regard to economic consequences.
ESA, in conjunction with the National Environmental Policy Act (NEPA),
is the main law that can prevent large civil infrastructures from
being built when ecosystems or species are threatened. NEPA was
enacted in 1969 with the goal of ensuring public input regarding
actions that affect their local environment. NEPA requires all agencies
to complete an environmental impact statement (EIS) analyzing the
effects of any major project that it plans to implement.
CASE: Tennessee Valley Authority vs. Hill, 1978 court
decision. A federal agency wanted to build the Tellico
Dam on a segment of the Little Tennessee River. A citizens'
group wanted to block the project and tried to do so under
NEPA. NEPA required the agency to do an assessment of the
environmental impacts caused by the proposed dam. In 1973,
a small endangered fish known as the snail darter was found
in the Little Tennessee River. The citizens' group filed a
lawsuit claiming that the dam would destroy the fish's habitat.
The court agreed and after many appeals, the 1978 Court of
Appeals stopped the project.
ESA works as follows:
ESA works as follows:
Listing: The Secretary of the Interior maintains a list of endangered
species, and a list of threatened species (likely endangered in
the future). A species is listed if any of these conditions applies:
a) present or threatened destruction, modification, or curtailment
of its habitat,
b) over utilization for commercial, recreational, scientific,
or educational purposes,
c) disease or predation impacts,
d) inadequacy of existing regulatory mechanisms, and
e) other natural or anthropogenic factors affect the existence.
There is no economic consideration at this stage.
habitat: The relevant agencies define a geographical area with
physical and biological features that are essential to species
survival. At this stage the agencies can consider economic impacts
to limit the area, therefore the area is not necessarily equal
to the entire habitat.
Plans: These are developed to include specific steps that must
be taken to help the species populations to increase in size.
Squad: overruling authority was added to help negotiate conflicts.
Williams, Ted. "False Forests," Mother Jones (Magazine).
Phillips, Kathryn. Tracking the Vanishing Frogs,
Wooster, Robert. The Military and United States Indian Policy
1865-1903 , Yale University Press, 1988.
Source: International Rivers Network, http://www.irn.org.
- Measures of Ecosystem Well Being (Bork)
the Earth's Environment
nature is a stranger yet;
The ones that cite her most
Have never passed her haunted house,
Nor simplified her ghost.
To pity those that know her not
Is helped by the regret
That those who know her
Know her less
The nearer they get."
Dickinson, cited by Margulis and Sagan in MICROCOSMOS,
we can characterize living organisms by various chemical, physical,
and biological parameters, the harmony that puts it all together
and forms the spark we call life is far from understood. We see
live organisms that may be stages toward more complete organisms.
Viruses, for example, are essentially a piece of DNA or RNA coated
with protein. It is by inserting this unit into cells of other animals
that viruses reproduce and continue their lives. Infective viruses
have been synthesized from elements. Several scientists have synthesized
DNA and RNA molecules that replicate themselves in a test tube.
But while we can concoct many of the molecules that must have been
in the primeval soup in which life evolved, we cannot yet compose
from elements a group of "cells that crawl out of a test-tube"
on their own, to paraphrase Margulis and Sagan.
do know a lot about the environmental conditions that sustain life.
We have begun to understand that not only does the environment sustain
life, but life in turn has made environmental conditions what they
are today. We now discuss some peculiar features and compounds on
Earth that make our environment particularly "fit" for
our kind of life. Much of this discussion is based on three sources:
Four Billion Years of Microbial Evolution, by Lynn Margulis
and Dorion Sagan, 1986.
Arrow and Evolution, by Harold F. Blum, 1951.
by James Lovelock, 1979
discusses the "fitness of the environment," a concept
originally proposed by Lawrence J. Henderson in 1913. Certain aspects
of the environment make the Earth particularly advantageous for
living organisms to live, develop, and evolve. The Earth's size
and its distance from the sun (a medium
yellow star), and the nature of the sun itself, determine the
gravitational force of the Earth and the amount and type of electromagnetic
energy we receive. These factors provide the conditions under which
life evolved, and that sustain life on Earth.
/ Discussion Questions:
List and draw a concept map of how Earth's gravity, its distance
from the sun, and the properties of sunlight affect factors
critical to a system of living organisms based on carbon,
hydrogen, and oxygen.
List the characteristics of a "live" system. Which
of these are not attainable by artificially-created systems
like a computer?
What do you think we would have to look for on another planet
to determine if there are life forms on it similar to ours?
Think of some parts of the Earth with an extreme environment
(extreme temperatures, pressures, etc.). Do organisms live
this go here? Or should it be a notecard on symbiosis?]
can adapt to extreme conditions through symbiosis. Photosynthesis
is an original adaptive mechanism developed in a species of bacteria
called cyanobacteria a billion years before plants evolved. These
seem to have eventually partnered with fungus-like organisms to
evolve into the cells of plants. The cyanobacteria have now become
the part of the plant called chloroplasts which are the photosynthetic
organelles of plants! This gives evidence to a symbiotic theory
of evolution. A group of bacteria live in animals intestines. Another
species live in the seabed seven hundred meters below the surface
of the Gulf of Mexico. Bacteria are responsible for nitrogen fixing
-- extracting nitrogen from the air and making it into nitrates
and NH3, which can then react with water to provide nutrients.
What is Life?
is not an inherent property of matter. Life is indeed
associated with matter, but it appears only under very specific
conditions and, when it does, it expresses itself in very diverse
and individual ways...We shall come closest to understanding
the principle of life if we can discover the principles according
to which life could begin...How life did begin,
however, can only be understood by appeal to historical evidence."
Manfred Eigen 1
alive is being sensitive to specific cues in the environment,
to transduce and amplify minute signals into definite actions.
Being alive is to achieve the long-range coordination of astronomical
numbers of submicroscopic, molecular reactions over macroscopic
distances. It is to be able to summon energy at will and engage
in extremely rapid and efficient energy transduction"
Mae-Wan Ho 2
is special about living systems and their relationship to the environment?
In this unit, we seek to understand some of the organizing principles
of living systems, recognizing with humility what Manfred Eigen
and Mae-Wan Ho say--that we can only understand what happened, not
why it did.
on the nature of life even for a short while brings to mind the
awesome variety, coherence, and organization in the functioning
of live organisms. Exchange of materials with the environment and
adaptation to environment are also evident. While we can try to
understand these interactions, and guess at how life might have
evolved on Earth, we can only guess at how life did begin
and survive. In the words of the Nobel Laureate Manfred Eigen, "life
is historical reality."
Eigen, Manfred. Steps Towards Life: A Perspective on Evolution.
Mae-Wan Ho. The Rainbow and the Worm, Singapore: World Scientific
Publications, 1994. p. 10
hydrogen, oxygen, nitrogen, phosphorus, and calcium form the major
chemical scaffolding of biological molecules. Hydrogen, nitrogen,
oxygen, phosphorus, and sulfur combined with carbon generated the
first group of compounds that eventually formed the chemical basis
of life. Other elements, such as iron, magnesium, sodium, potassium,
chlorine, and iodine also play specific and vital roles.
oxygen, and carbon make up over 93% of the weight of the human body.
Water is almost 80-90% by weight of all living organisms. Water
has several physical and chemical
properties that make it important in maintaining conditions
fit for life on Earth.
<student exercise on water?>
The large amount of water on the Earth's surface and the fact that
at the average temperature over most of the Earth, water is in a
liquid state, are both important to life. Water constitutes the
largest fraction of most organisms.
spread evenly over the Earth, the water present on Earth could form
a layer about 2.5 km (1.6 miles) thick. Water has a high heat capacity.
It can absorb quite a bit of heat (1 calorie for every gram for
each degree rise in temperature) before its temperature rises significantly.
This provides a moderating influence that prevents sudden rises
in temperature, which could be damaging to live organisms. Water
bodies on Earth work to moderate atmospheric temperature changes,
and internal water helps organisms maintain temperature ranges.
also has a large latent heat
of vaporization because a lot of energy is needed to break hydrogen
bonds among water
molecules. It takes a lot of heat to change liquid water to
vapor--560 calories/gram. Thus organisms (plants and animals) can
dissipate a lot of heat by having some of the water in them evaporate.
For example, we are able to evaporate water from our body, as sweat,
cooling the body because of the heat removed by the evaporating
has a high latent heat of fusion as well. Eighty calories are required
to convert 1 gram of ice to water. In addition, because of the peculiarities
of the hydrogen bond, ice is less dense than water. It rarely happens
that a solid material is less dense than its liquid state. Ice also
does not conduct heat well. The high latent heat, low heat conductivity,
and low density of ice causes ice to float on water, keeping the
warmer water sealed below the insulating ice layer on lakes and
other bodies of water, and keeping the water habitable for aquatic
is a "universal" solvent. It is capable of dissolving
a variety of materials. Salts dissolve in water to form ions
because of the polar nature of the H2O molecule. As described
in the Science Notes of the Energy System, water is a polar
molecule. It has a positive and a negative end. The longer time
spent by the covalent electrons near the oxygen atom makes the oxygen
end negatively charged overall. Various ions play important roles
especially in the conduction of nerve impulses. Balance of ionic
flow across cell membranes (cell walls) are also an important mechanism
of moving nutrients as well as in several other cell functions.
water vapor is one of the greenhouse gases that keeps the Earth's
atmosphere at the temperatures
suited to life.
Many of the special properties of water come from
hydrogen. The small size of the hydrogen atom makes it possible
to fit into many more molecular configurations than a bigger atom
can. Thus hydrogen can form numerous compounds. Hydrogen is light,
so all hydrogen gas could have escaped the Earth's gravitational
pull when the Earth was still very hot.
However, its high chemical reactivity with nitrogen, oxygen, and
carbon, and the abundance of these elements made it possible for
the Earth to retain a large amount of hydrogen in combination with
these elements as ammonia, water, and methane during the primitive
days of the Earth.
The carbon compounds
that make up essential molecules such as proteins are described
in the notes on biological molecules. Carbon is second only to hydrogen
in the number of compounds it can form, oxygen being the third in
this capability. Carbon can form more than 2500 compounds with hydrogen
alone. The next elements that form most hydrides are boron and nitrogen;
each of which can form only seven! The C-C bonds make possible a
great variety of molecules with different chains and rings. C, H,
and O combine together to from even a richer variety of compounds.
The same number of atoms can yield completely different compound
depending on the arraignment of atoms. For example, C can form butyl
alcohol (the prefix butyl refers to four carbons) in two alternate
forms with slightly different but similar properties.
-OH group is the hallmark group of an alcohol. These same number
of atoms could also form an ether characterized by the -O- bond
between carbon groups. Thus these atoms can form diethyl ether,
two ethyl (C2H5) groups bridged by O, as in:
much larger molecules with many C atoms, the possible arrangements
become very large. Recall
that carbon is the middle element in the first period of the Periodic
Table. It has four electrons (1s22s22p2)
in the outer shell, needing four more to complete the outer shell.
This capacity to form four covalent bonds makes for the capability
of carbon to form compounds. The
four bonding electrons and various spatial arrangements give carbon
its enormous versatility.
versatility and the fact that carbon dioxide is a gas at ordinary
temperatures are two important aspects in carbon being the chemical
basis of life. Photosynthesis occurs because CO2 is a
gas and is soluble in H2O, so that this mixture, with
energy from the violet part of sunlight, can form sugars.
versatility of carbon comes from its central position in the periodic
table. People have conjectured why silicon in an analogous position
and, being one of the most plentiful elements in the Earth's crust,
did not become that centerpiece. SiO2 is found in the
solid form in plenty--as sand. But it becomes a gas at only 3000°,
and it is not soluble in water. The chemical versatility of silicon
is indeed the property we value for its use for computers.
With carbon and hydrogen, oxygen forms the third principal element
in living systems. As we see later in this unit, our atmosphere
was not always oxygen-rich. About 2000 million years ago, there
was only about 0.0001% oxygen in the atmosphere. During the Archean
and Proterozoic ages (when plants started to use photosynthesis),
was a radical increase of the O2 concentration to the
almost 20% that it is today. This resulted in a major extinction
of some bacteria as discussed in a later section.
silicon is to carbon, so is sulfur to oxygen. So we could imagine
a material and life configuration where H2S instead of
H2O was the basic "liquid" of life. (H2S
is actually a gas at Earth's average temperatures.) However the
H-O bond is stronger than the H-S, and oxygen is 50 times more plentiful
on Earth than sulfur. There
are some organisms that use sulfur. This is discussed in the section
The other elements that play a vital role in living systems are
N, Ca, P, Na, Fe, K, Cl, S, Zn, and Mg. Together these form about
1.72 atomic percent of the human body. Along with H, O, and C, these
elements account for 99.96% of the human body. Lighter elements
dominate this list and these elements have more specific roles in
the function of biological molecules than the more general C, O,
and H trio.
and sulfur are components of all proteins. Phosphorus is an essential
component for the storage and use of energy in all cells. Cellular
energy resides in phosphate bonds. Mg is a central component of
chlorophyll, and iron is a component of hemoglobin and other respiratory
enzymes. These elements serve very specialized but important functions.
such as Fe and Na are rare in the body but play important roles
either in very specific molecules as Fe in hemoglobin, Zn in gene
transcription proteins, or Mg in chlorophyll; or with a specific
function such as Na or K ions providing the flow of ions for conduction
of information along nerves. Most metals, however, are toxic to
most organisms. Examples of metal toxicity that have become significant
environmental problems in the last half-century are cases of lead
poisoning, mercury poisoning (Minamata
and poisoning by metals such as chromium (Cr), aluminum (Al), and
cadmium (Cd). The amounts of chromium and cadmium in the environment
have increased due to numerous technological uses ranging from steel
production to household batteries.
Energy for Life
said at the outset that the ability of certain molecules to capture
and use small amounts of energy efficiently is a central aspect
of life. The continuous chemical reactions and changes that go on
in an organism is called metabolism. Accumulation and use
of energy is the basis of metabolism.
the long run, almost all the energy for life on Earth comes from
sunlight, through photosynthesis by plants. Energy is stored as
potential energy in chemical bonds of carbon compounds. This is
our "free reserve."
X: Cycle of photosynthesis and
oxidation -- energy capture and release.
X shows the cycle of energy transformation overall.
and Energy Storage
In most of photosynthesis, electromagnetic energy from sunlight
is used to store chemical potential energy through oxidation
of water, using CO2 for the carbon.
+ H2O + sunlight energy
rich carbon compounds + O2 + heat
equation may be written in general as:
+ H2O + sunlight (CH2O)n
(CH2O)n is the generic name for the energy-rich
compounds--sugars and starches such as C6H12O6
[(CH2O)6] or C11H22O11
of the energy captured is lost
as heat. Photosynthesis is less than 1% efficient--only 1% or so
of the total energy falling on leaves is used for photosynthesis--mainly
the blue and ultraviolet region. Because photosynthesis only uses
blue and ultraviolet wavelengths of energy, it only actually captures
energy from a small fraction of the solar
spectrum. Then again only 1% of this captured energy is converted
appear green because they reflect most of the sunlight in the
visible region. The main molecules responsible for photosynthesis
is the family of pigments called chlorophyll (NOTE: Pigments are
light absorbing molecules that by absorbing light preferentially
of one or a set of wavelengths gives the color to the material that
contains them.) Chlorophylls are formed in cell bodies called chloroplasts.
Chlorophyll and other similar energy-transforming molecules (phycocyanin,
fucoxanthin, phycoerythrin) are characteristic of autotrophic organisms.
Autotrophs are organisms that are able to manufacture their own
basic supply of energy-rich carbon compounds from CO2.
Heterotrophs (like us) on the other hand, have to be supplied with
energy-rich carbon compounds from outside sources. All autotrophs
reduce CO2 to carbohydrates (written in general as (CH2O)n)
or related organic compounds.
may also occur through oxidation of compounds other than water.
There are a few bacteria called chemoautotrophic bacteria that get
their energy for storage not from light (photosynthesis) but from
other inorganic chemicals (chemosynthesis). Many of these bacteria
can also do without pure oxygen as long as they have CO2
and energy from chemical bonds. Thus some use H2S found
in volcanic ash and make (CH2O) according to:
+ 2H2S + sunlight or chemical bond
+ H2O + 2S
sulfur can use bond energy from H2S instead of sunlight.
Recall how we said in the previous section that sulfur could have
been a "contender" for the position oxygen holds in making
species oxidize H2:
+ 2H2 [CH2O]
even some complicated molecule like isopropanol:
+ 2CH3CHOHCH3 [CH2O]
+ H2O + 2CH3COCH3
general, photosynthesis may be written as:
+ 2H2A [CH2O]
+ H2O + 2A
H2A (e.g. H2O, H2S) is the compound
that gets oxidized to A. The role of H2A is to donate
hydrogen to make the energy-rich carbohydrates (CH2O)n
from CO2. <<NOTE
oxidation is the process--often a series of processes--by which
the energy in (CH2O)n is eventually used by the organism
with the final products being CO2 and H2O
which are excreted. Glucose is a type of sugar made through photosynthesis.
The oxidation of glucose can be used as an example to show the oxidation
+ 6CO2 + 688 kcal/mole
oxygen that comes into the body through respiration enables the
biological oxidation (or "combustion) of carbohydrates with
the release of energy. Note that this energy is of a different type
than the original light energy which helped form the sugar.
the similarity of this reaction to the burning
of coal described in the Energy System. We had to have high
temperatures for the combustion of coal. Compared to that, our combustion
takes place at low (body) temperatures. Glucose is a complex
and it breaks down in steps. Actually, this breakdown happens very
very slowly at normal temperatures. Certain catalysts--enzymes and
coenzymes--speed these up as needed, in the absence of heat.
compounds used for energy are not directly derivable from glucose.
The vertebrate animals use carbohydrates, fats, and proteins to
store energy. These are broken down into smaller units before oxidation
begins. Adenosine triphosphate (ATP) and adenosine diphosphate (ADP)
play a unique role in mobilizing and transforming energy in living
systems. The phosphate bonds in ATP and ADP are used to transfer
energy. It takes a long chain of processes to eventually complete
the breakdown of sugars and starches to H2O and CO2,
material being constructed and deposited along the way.
Y: Adenosine monophosphate.
shows the structure of adenosine monophosphate, made of the
protein adenine and the sugar ribose with a phosphate group hanging
at the side. One or two more phosphate groups can be linked on to
the phosphate in AMP to give ADP and ATP respectively. The ADP phosphate
bond is about 10 kcal/mole and breaking and building this (the ADP-ATP
cycle) transfers energy from glucose to where it is needed. The
high energy phosphate bond is denoted by ~ph. This reaction, called
phosphorylation, is represented in the equation:
+ ATP glucopyromose-6-phosphate
+ ~ph GP6P
has higher energy than glucose and we say the glucose has been phosphorylated.
This compound can take part in reactions that glucose cannot, and
use the energy in these reactions. One example is muscular contraction,
where the ~ph bonds transfer the energy needed.
of the extraction of energy and sugar breakdown occurs through fermentation
of sugars to alcohol and acids (alcohols have the -OH group, acids
have the -COOH group).
& the Environment
is defined as the gradual change of any object, in our case, the
biological system, through time. We discussed briefly in the previous
section some of the aspects of the complex intricate system of the
chemistry of biomolecules. We now shift to the level of the organism--cells
organized into tissues, organs, and organism--which have persisted
and changed through time. Broadly speaking, the first single-celled
organism did not have a nucleus. These prokaryotes persist
today as microbes, such as bacteria and viruses.
synthesis was an early step in the evolution of organisms who were
then capable of reproducing themselves using their RNA. It is not
clear when the first cells in the form we know now were formed.
Somewhere, in the primordial soups, some molecules got enclosed
inside a membrane to form a cell. RNA molecules within this cell
could then facilitate reproduction of the cell. All we can surmise
is that this aggregation of molecules started about 3.5 billion
years ago. It is believed that RNA came after proteins and enzymes
evolved. Once a cell was established, RNA evolved into DNA, making
a subcellular structure we now call the nucleus. The DNA, which
is a coil of two strands of RNA (with the bases A, C, G, and T,
whereas RNA has A, C, G, U), is the molecule that enables protein
of the prokaryotic bacteria we know like mycoplasms, as well as
different varieties of bacillus, e-coli, and staphylococcus, still
abound on Earth. Bacteria live in an enormous variety of environments,
often symbiotic with other organisms. Thus benign forms of e-coli
live in our guts and numerous bacteria live in soil and in plants.
Species of bacteria can use a variety of organic molecules such
as sugars and polypeptides as their food. Bacteria are the most
abundant type of cell on earth. The early bacteria seemed to have
used ATP to store the energy of sunlight. Blue-green algae is a
type of bacteria that converts CO2 and N2
into its food.
plants developed the capability of photosynthesis, the composition
of the early atmosphere (mostly CO2) began to change over billions
of years to this current
composition of 20% oxygen and only traces of CO2
as the plants "fixed" the carbon. Many of the early bacteria
were used to an oxygen-poor environment and several of them then
became extinct. Others formed a symbiotic association with oxygen--using
(aerobic) types of cells to form the present day cells with nuclei
(eucaryotes). The different organelles in the cell such as the chloroplasts
and mitochondria are now believed to have been separate organisms
that originally associated with each other to form mutually beneficial
colonies we call cells.
we noted before, life on Earth has evolved around the chemical versatility
of a few atoms, especially carbon. Some special features of chemistry
are used by living systems. These features are:
ability of carbon to combine in so many different ways;
unique properties of water; and
ability of organic molecules to use small amounts of energy efficiently.
live organism is an open system, continuously exchanging energy
and matter with the environment. It is "self-organizing,"
meaning it takes raw material and reassembles it into complex vital
molecules. During this process, life increases internal order (decreases
local entropy). Thus life builds up information (order) which is
early environment on Earth is a matter of conjecture. Piecing together
evidence, it is believed now that the environment consisted of high
energy events such as volcanic eruptions, continuous torrents of
rain, and large amounts of lightning. It is believed that there
was little if any oxygen in the atmosphere, and certainly no ozone
layer. Therefore, ultraviolet from the sun could reach all the way
to the Earth's surface.
of our models for the early environment of Earth come from the observation
of the atmospheres of Mars and Venus, made by NASA.
X shows the major gases in the atmosphere of Venus, Mars and the
Earth. Note the difference between the estimate of the composition
with and without life on earth.
as it is
X: Atmospheric compositions of Venus, Mars and Earth (with
and without life)
[from GAIA by James Lovelock , 1995 edition]
has been shown in laboratory experiments that simple carbon-based
(organic) molecules are formed under these early conditions that
prevailed on Earth. In 1953, Stewart Miller, a graduate student
of the famous chemist, Harold Urey, simulated the early (prebiotic)
atmosphere on Earth--a mixture of ammonia (NH3), water
vapor (H2O), hydrogen, and methane (CH4).
He bombarded the mixture with electrical discharges to simulate
lightning. In a week, he saw some spectacular results: alanine and
glycine, two amino acids that form proteins in life forms today
(including humans) were formed in the resulting mixture. Under the
conditions provided, more complex molecules such as formaldehyde
(HCHO), formic acid (HCOOH), and hydrogen cyanide (HCN) had formed.
In a water solution these molecules had then reacted with each other
to form more complex organic molecules such as acetic acid (CH3COOH),
glycine (NH2CONH2), alanine (NH2CHOHCOOH).
richness of carbon chemistry and the plethora of carbon compounds
form the basis of life on Earth. Carbon chemistry (called organic
chemistry) and the function of biomolecules are explained in detail
in the section on carbon compounds.
the late 1970's, Elso Barghoom of Harvard University was looking
for the earliest evidence of life, and found it eventually in Swaziland,
Africa. He found evidence of bacteria in 3.4 billion year old fossils.
This means that life started very early on our 4.5 billion year
old planet. The time it took to move from inanimate matter to the
first forms of life was actually shorter than that to move from
bacteria to larger organisms--the earliest of which appear to be
only 570 million years old, as evidenced by hard-shelled fossils
of that age that appear all over the Earth.
life then probably came from mixtures of materials combining to
form biomolecules with the energy provided by ultraviolet light
and lightning. Replication of DNA and mutation in rapidly dividing
bacteria, as well as local variations in environment, then provided
a route to diverse populations of bacteria. Development of metabolic
pathways to store and convert energy--mechanisms of fermentation
to break down sugars--was an early step. Along the way the bacteria
also began to capture atmospheric nitrogen to begin the manufacture
of amino acids and other organic compounds. To this day, we need
bacteria to take the stable nitrogen gas N2 from the
atmosphere and convert it into usable compounds. This "nitrogen-fixing"
is discussed under the nitrogen cycle in the Materials System.
and Sagan also state that "the evolution of photosynthesis
is undoubtedly the most important single innovation in the history
of life on the planet" (p. 78). The first photosynthetic organisms
were bacteria that used H2S rather than H2O.
H2S must have been plentiful, emitted from volcanoes.
The development of the successive stages of bacterial development
is fascinating as described by Margulis and Sagan. Early adaptations
included developing pigments to protect against ultraviolet, then
top layers protecting the layers below and developing repair enzymes.
Repair enzymes persist in us today. When ultraviolet or other ionizing
radiation damages part of our DNA, these enzymes remove the damaged
portion and replace it with new healthy DNA. Despite the fact that
we have had an ozone layer to
filter out the almost all ultraviolet for over 2 billion years now,
we still have this repair system.
pigmentosum is a rare genetic defect inhibiting DNA repair mechanisms
against ultraviolet radiation damage. It is characterized by severe
sensitivity to all sources of UV radiation (especially sunlight),
and often results in cutaneous lesions, premature aging of the skin,
cataracts, increased risk of ocular benign and malign tumors, and
sometimes neurological disorders such as mental retardation. To
learn more about XP, visit the Xeroderma
or read its disease description at the Atlas
of Genetics and Cytogenetics in Oncology and Haematology.
Co-Evolution of Climate and Life
is the Greek goddess of the Earth. While designing experiments for
NASA to detect life on Mars, the atmospheric chemist James Lovelock
developed the theory called Gaia. Gaia refers to the system of all
life on Earth and the atmosphere which mutually regulates prevailing
conditions to continue life on Earth. The name "Gaia"
was suggested to Lovelock at his request by his neighbor, William
Golding, author of Lord of the Flies.
Gaia hypothesis states that the biota (group of all living organisms)
regulate the temperature and gas composition of the atmosphere.
Lovelock came to this conclusion because the 20-80 composition of
O2- N2 in our atmosphere can not be explained
by laws of physics and chemistry alone. If we were to make a simple
mixture of these gases in the laboratory along with some of the
other materials on Earth, the gases would react quickly and become
compounds, and not remain as O2 and N2 in
the gaseous state. Lovelock therefore postulated that this unlikely
mixture must be aided by the continuous production of these gases
by live organisms! If this were not true, our atmosphere would be
a mixture of N2, NH3, SOx, CH4,
methyl chloride (CH2Cl), and others. These are indeed
present but only in minute quantities.
addition, the Earth's average temperature has remained relatively
stable (around 22° C) despite the increase in the sun's temperature
over the past 4 billion years. This too has been attributed by Lovelock
to the feedback effects of life on the atmosphere.
to add material)
scientists disagree with Lovelock's hypothesis. Lovelock has actually
modeled a simple system, "Daisy World," a planet with
black and white daisies circling a sun-like star. He and his co-author,
Andrew Watson, have demonstrated the Gaia-like character of this
world. The daisies act as thermostats, stabilizing the temperature.
In our world, microbes can play the role of the daisies. Margulis
and Sagan cite the discovery that about 20,000 years ago there was
only two-thirds the amount of CO2 that we have now, and
that the rise of CO2 to pre-industrial levels took place
abruptly in a 100 year span. This cannot be explained by geophysical
or chemical processes alone, but could be the result of a sudden
species death of algae.
stuff from Gaia)
Gaia or Daisyworld links and add...)