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THE BIOSPHERE (DOC) Powered By Docstoc
					                         THE BIOSPHERE
The term "Biosphere" was coined by Russian scientist Vladimir Vernadsky in the
1929. The biosphere is the life zone of the Earth and includes all living organisms,
including man, and all organic matter that has not yet decomposed.
The biosphere is the outermost part of the planet's shell — including air, land, surface
rocks and water — within which life occurs, and which biotic processes in turn alter or

From the broadest geophysiological point of view, the biosphere is the global
ecological system integrating all living beings and their relationships, including their
interaction with the elements of the lithosphere (rocks), hydrosphere (water), and
atmosphere (air).

Our planet Earth is the only place where life is known to exist. This biosphere is
postulated to have evolved, beginning through a process of biogenesis or biopoesis,
at least some 3.5 billion years ago.

The Environmental System
The environmental system may be understood in an ecological sense as the set of
interactions between the elements of the biosphere, which includes the atmosphere,
the hydrosphere, the lithosphere and the ecosphere . We present here a brief
description of each system.
•      The atmosphere is a mixture of nitrogen (78%), oxygen (21%), and traces
(remaining 1%) of carbon dioxide, argon, water vapor and other components.
Although the atmosphere is approximately 1,100 km high, the stratosphere (10 to 50
km) and the troposphere (less than 10 km) are the main atmospheric interactors of
the biosphere. The atmosphere is a prime mean for the spatial diffusion of pollutants
and a temporary mean of their accumulation.

•      The hydrosphere is the accumulation of water in all its states (solid, liquid and
gas) and the elements dissolved it in (sodium, magnesium, calcium, chloride and
sulphate). 97% of the water forms the oceans, 2% is ice (north and south poles) and
1% forms rivers, lakes, ground water and atmospheric vapor. It covers around 71% of
the earth's surface and is an important accumulator of pollutants and a significant
vector of diffusion.

•      The lithosphere is the thin crust between the mantle and the atmosphere.
Although the lithosphere is around 100 km thick, only 1 km of it can be considered in
interaction with the biosphere. Main constituents are oxygen (47%), silicon (28%),
aluminum (8%), iron (5%), calcium (4%), sodium (3%), potassium (3%) and
magnesium (2%) in a crystalline state. The lithosphere is the main source of
pollutants and a permanent accumulator. Some are naturally released through
sources like volcanic eruptions, while others like fossil fuels are the result of artificial
extraction and combustion.

•      The ecosphere is the set of all living organisms, including animals and
vegetal. They are temporary accumulators (like lead) and sources for pollutants
(natural forest burning) in a very complex set of relationships with the atmosphere,
hydrosphere and lithosphere.
Extent of the earth's biosphere

Some theorists have postulated that the Earth is poorly suited to life, although nearly
every part of the planet, from the polar ice caps to the Equator, supports life of some
kind. Indeed, recent advances in microbiology have demonstrated that microbes live
deep beneath the Earth's terrestrial surface, and that the total mass of microbial life
in so-called "uninhabitable zones" may, in biomass, exceed all animal and plant life
on the surface. The actual thickness of the biosphere on earth is hard to measure.

Birds typically fly at altitudes of 650 to 2000 meters, and fish that live deep
underwater can be found down to -8,372 meters in the Puerto Rico Trench.
There are more extreme examples for life on the planet: Rüppell's Vulture has been
found at altitudes of 11,300 meters; Bar-headed Geese migrate at altitudes of at least
8,300 meters (over Mount Everest); Yaks live at elevations between 3,200 to 5,400
meters above sea level; mountain goats live up to 3,050 meters. Herbivorous animals
at these elevations depend on lichens, grasses, and herbs but the biggest tree is the
Tine palm or mountain coconut found 3,400 meters above sea level.

Microscopic organisms (e.g., bacteria) live at such extremes that, taking them into
consideration puts the thickness of the biosphere much greater, but at minimum it
extends from 5,400 meters above sea level to at least 9,000 meters below sea level.

Our biosphere is divided into a number of biomes, inhabited by broadly similar flora
and fauna. On land, biomes are separated primarily by latitude. Terrestrial biomes
lying within the Arctic and Antarctic Circles are relatively barren of plant and animal
life, while most of the more populus biomes lie near the Equator. Terrestrial
organisms in temperate and arctic biomes have relatively small amounts of total
biomass, smaller energy budgets, and display prominent adaptations to cold,
including world-spanning migrations, social adaptations, homeothermy, estivation
and multiple layers of insulation.

Important major components of Earth's biosphere are : Ocean; Forest; Desert;
Steppe; Lake; River.

Ecosystems are not isolated from each other, but are interrelated. For example,
water may circulate between ecosystems by the means of a river or ocean current.
Water itself, as a liquid medium, even defines ecosystems. Some species, such as
salmon or freshwater eels move between marine systems and fresh-water systems.

 These relationships between the ecosystems lead to the concept of a biome.
Biomes correspond rather well to subdivisions distributed along the latitudes, from
the equator towards the poles, with differences based on to the physical environment
(for example, oceans or mountain ranges) and to the climate. Their variation is
generally related to the distribution of species according to their ability to tolerate
temperature and/or dryness. For example, one may find photosynthetic algae only in
the photic part of the ocean (where light penetrates), while conifers are mostly found
in mountains.

Though this is a simplification of more complicated scheme, latitude and altitude
approximate a good representation of the distribution of biodiversity within the
biosphere. Very generally, the richness of biodiversity (as well for animal than plant
species) is decreasing most rapidly near the equator and less rapidly as one
approaches the poles.

The biosphere may also be divided into ecozone, which are very well defined today
and primarily follow the continental borders. The ecozones are themselves divided
into ecoregions, though there is not agreement on their limits.

A biome is a large, distinctive complex of plant communities created and maintained
by climate.

In ecology, a biome is a major regional group of distinctive plant and animal
communities best adapted to the region's physical natural environment, latitude,
altitude, and terrain. A biome is made up of communities at stable steady state and
all associated transitional, disturbed, or degraded, vegetation, fauna and soils, but
can often be identified by the climax vegetation type.

The nature of communities and ecosystem on land is shaped primarily by the
dominant producers. It is the plants that provide the framework for the overall
structure and potential relationships within the natural systems of a region. Although
the biodiversity patterns of different parts of the earth's surface can be quite different,
there can be a remarkable similarity in the aspect of communities and ecosystems
developed under similar climates. Thus, while the specific plants which are present in
a rainforest in South America are quite different from those in a rainforest in the
Congo, the two forests will be quite similar in terms of the scope of biodiversity and
the ways in which niche space is partitioned. Put simply, rainforests, as one example,
will look quite similar from one biogeographic region to another, despite profound
differences in the specific plants and animals that make up these forests. These
broad zones, with their definable characteristics, are known as biomes.

Climate, specifically, temperature and rainfall, is the most important factor in defining
the nature of the biomes that develop within specific regions:
This diagram, shows the relationship of rainfall (dry to wet) and temperature (warm to
cold) in defining the distribution of some of the major terrestrial biomes.

Biomes are often given local names. For example, a Temperate grassland or
shrubland biome is known commonly as steppe in central Asia, savanna or veld in
southern Africa, prairie in North America, pampa in South America and outback or
scrub in Australia. Sometimes an entire biome may be targeted for protection,
especially under an individual nation's Biodiversity Action Plan.
A fundamental classification of biomes is into:
1.     Terrestrial (or continental) biomes and
2.     Aquatic biomes.

Terrestrial Biomes:
How many biomes are there?
There are more than 150 different terrestrial "biomes or ecoregions" in the world. But
8 of them are main terrestrial biomes; which are:
•      tundra
•      taiga
•      temperate deciduous forest
•      scrub forest (Chaparral)
•      grassland
•      desert
•      tropical rain forest
•      temperate rain forest
Tropical Rain Forest

In the Western Hemisphere, the tropical rain forest reaches its fullest development in
the jungles of Central and South America.
•       The trees are very tall and of a great variety of species.
•       One rarely finds two trees of the same species growing close to one another.
•       The vegetation is so dense that little light reaches the forest floor.
•       Most of the plants are evergreen, not deciduous.
•       The branches of the trees are festooned with vines and epiphytes.
Epiphytes are plants that live perched on sturdier plants. They do not take
nourishment from their host as parasitic plants do. Because their roots do not reach
the ground, they depend on the air to bring them moisture and inorganic nutrients.
Many orchids and many bromeliads (members of the pineapple family like "Spanish
moss") are epiphytes.
The lushness of the tropical rain forest suggests a high net productivity, but this is
illusory. Many of the frequent attempts to use the tropical rain forest for conventional
crops have been disappointing. Two problems:
•       The high rainfall leaches soil minerals below the reach of plant roots.
•       The warmth and moisture cause rapid decay so little humus is added to the
More on jungle soils.
The tropical rain forest exceeds all the other biomes in the diversity of its animals as
well as plants. Most of the animals — mammals and reptiles, as well as birds and
insects — live in the trees.

Temperate Deciduous Forest

This biome occupies the eastern half of the United States and a large portion of
Europe. It is characterized by:
•      hardwood trees (e.g., beech, maple, oak, hickory) which
•      are deciduous; that is, shed their leaves in the autumn.
•      The number of different species is far more limited than in the jungle.
•      Large stands dominated by a single species are common.
•      Deer, raccoons, and salamanders are characteristic inhabitants.
•      During the growing season, this biome can be quite productive in both natural
and agricultural ecosystems.
The taiga is named after the biome in Russia.
•      It is a land dominated by conifers, especially spruces and firs.
•      It is dotted with lakes, bogs, and marshes.
•      It is populated by an even more limited variety of plants and animals than is
the temperate deciduous forest.
•      Before the long, snowy winter sets in, many of the mammals hibernate, and
many of the birds migrate south.
•      Although the long days of summer permit plants to grow luxuriantly, net
productivity is low.


At extreme latitudes, the trees of the taiga become stunted by the harshness of the
subarctic climate. Finally, they disappear leaving a land of bogs and lakes.
•      The climate is so cold in winter that even the long days of summer are unable
to thaw the permafrost beneath the surface layers of soil.
•      Sphagnum moss, a wide variety of lichens, and some grasses and fast-
growing annuals dominate the landscape during the short growing season.
•      Caribou feed on this growth as do vast numbers of insects.
•      Swarms of migrating birds, especially waterfowl, invade the tundra in the
summer to raise their young, feeding them on a large variety of aquatic invertebrates
and vertebrates.
•      As the brief arctic summer draws to a close, the birds fly south, and
•      all but a few of the permanent residents, in one way or another, prepare
themselves to spend the winter in a dormant state.

Temperate Rain Forest

The temperate rain forest combines high annual rainfall with a temperate climate. An
annual rainfall of as much as 150 inches produces a lush forest of conifers.


Grasslands are also known as prairie or plains. The annual precipitation in the
grasslands averages 20 in./year. A large proportion of this falls as rain early in the
growing season. This promotes a vigorous growth of perennial grasses and herbs,
but — except along river valleys — is barely adequate for the growth of forests.
Fire is probably the factor that tips the balance from forest to grasslands. Fires — set
by lightning and by humans — regularly swept the plains in earlier times. Thanks to
their underground stems and buds, perennial grasses and herbs are not harmed by
fires that destroy most shrubs and trees.
The abundance of grass for food, coupled with the lack of shelter from predators,
produces similar animal populations in grasslands throughout the world. The
dominant vertebrates are swiftly-moving, herbivorous ungulates. In North America,
bison and antelope were conspicuous members of the grassland fauna before the
coming of white settlers.
Now the level grasslands supply corn, wheat, and other grains, and the hillier areas
support domesticated ungulates: cattle and sheep.
When cultivated carefully, the grassland biome is capable of high net productivity. A
major reason: rainfall in this biome never leaches soil minerals below the reach of the
roots of crop plants.


Annual rainfall in the desert is less than 10 in. and, in some years, may be zero.
Because of the extreme dryness of the desert, its colonization is limited to
•     plants such as cacti, sagebrush, and mesquite that have a number of
adaptations that conserve water over long periods;
•     fast-growing annuals whose seeds can germinate, develop to maturity, flower,
and produce a new crop of seeds all within a few weeks following a rare, soaking

Many of the animals in the desert (mammals, lizards and snakes, insects, and even
some birds) are adapted for burrowing to escape the scorching heat of the desert
sun. Many of them limit their forays for food to the night.
The net productivity of the desert is low. High productivity can sometimes be
achieved with irrigation, but these gains are often only temporary. The high rates of
evaporation cause minerals to accumulate near the surface and soon their
concentration may reach levels toxic to plants.

Scrub Forest

The annual rainfall in the scrub forest biome may reach 20–30 in., but in contrast to
the grasslands, almost all of this falls in winter. Summers are very dry and all the
plants — trees, shrubs, and grasses — are more or less dormant then.
Similar biomes (with other names, such as scrub forest, are found around much of
the Mediterranean Sea, California and along the southern coast of Australia.
The trees are mostly oaks, both deciduous and evergreen. All of these plants are
adapted to drought by such mechanisms as waxy, waterproof coatings on their
The scrub forest has many plants brought to it from similar biomes elsewhere.
Vineyards, olives, and figs flourish just as they do in their native Mediterranean
biome. So, too, do eucalyptus trees transplanted from the equivalent biome in

Aquatic Biomes:
There are different types of aquatic biomes like:
•     continental shelf
•     littoral/intertidal zone
•     riparian
•     pond
•     coral reef
•     kelp forest
•     pack ice
•     hydrothermal vents
•     cold seeps
•     benthic zone
•     pelagic zone
•     neritic zone

Some examples for most important and common aquatic biomes are:

Continental Shelf

The continental shelf is the extended perimeter of each continent, which is covered
during interglacial periods such as the current epoch by relatively shallow seas
(known as shelf seas) and gulfs. The shelf usually ends at a point of increasing slope
(called the shelf break). The sea floor below the break is the continental slope. Below
the slope is the continental rise, which finally merges into the deep ocean floor, the
abyssal plain.

Intertidal zone (Littoral Zone)

The intertidal zone, also known as the littoral zone, in marine aquatic environments is
the area of the foreshore and seabed that is exposed to the air at low tide and
submerged at high tide, ie the area between tide marks.
The most common organisms in the intertidal zone are small and relatively
uncomplicated. This is for a variety of reasons; firstly the supply of water which
marine organisms require to survive is intermittent. Secondly, the wave action around
the shore can wash away or dislodge poorly suited or adapted organisms. Thirdly,
because of the intertidal zone's high exposure to the sun the temperature range can
be extreme from very hot to near freezing in frigid climates (with cold seas). Lastly,
the salinity is much higher in the intertidal zone because salt water trapped in rock
pools evaporates leaving behind salt deposits. These four factors make the intertidal
zone an extreme environment in which to live.
A typical rocky shore can be divided into a spray zone (also known as the Supratidal
Zone, which is above the spring high-tide line and is covered by water only during
storms, and an intertidal zone, which lies between the high and low tidal extremes.
Along most shores, the intertidal zone can be clearly separated into the following
subzones: high tide zone, middle tide zone, and low tide zone.

A rock, seen at low tide, exhibiting typical intertidal zonation.

Riparian Zone

Riparian zone is the interface between land and a flowing surface water body. Plant
communities along the river margins are called riparian vegetation, characterized by
hydrophilic plants. Riparian zones are significant in ecology, environmental
management and civil engineering due to their role in soil conservation, their
biodiversity and the influence they have on aquatic ecosystems. Riparian zones
occur in many forms including grassland, woodland, wetland or even non-vegetative.
In some regions the terms riparian woodland, riparian forest, riparian buffer zone or
riparian strip are used to characterize a riparian zone.

A pond is characterized as being a small body of water that is shallow enough for
sunlight to reach the bottom, permitting the growth of rooted plants at its deepest
point. Seldom do ponds reach more that 3.6-4.5 meters (12 to 15 feet) in depth.

Coral Reefs

Coral reefs (also known as Sea Gardens) are barriers consisting of coral skeletons
built upon coral skeletons. They grow in tropical seas in the photic zone, where there
is mild wave action, not so strong it tears the reef apart yet strong enough to stir the
water and deliver sufficient food and oxygen. Coral reefs also need nutrient-poor,
clear, warm, shallow water to grow. The coral skeletons while alive house coral

Kelp Forest

Kelp forests are a type of marine ecosystem established around colonies of kelp;
they contain rich biodiversity. Kelp can stretch 2-30 meters or more (up to 60 m in
Macrocystis pyrifera) from their anchors on the sea floor to the surface, providing a
vertical infrastructure that is home to many fish and invertebrate species. Kelp forests
also often attract mammalian visitors, including whales, sea lions, and sea otters.
Kelp forests draw their name from an analogy to forests on land.
Pack ice

Pack ice is formed from seawater in the Earth's polar regions, and coverage
increases during winter. In spring and summer, when melting occurs, the margins of
the sea ice retreat. The vast bulk of the world's sea ice forms in the Arctic ocean and
the oceans around Antarctica. The Antarctic ice cover is highly seasonal, with very
little ice in the austral summer, expanding to an area roughly equal to that of
Antarctica in winter. Consequently, most Antarctic sea ice is first year ice, up to 1
meter thick. The situation in the Arctic is very different (a polar sea surrounded by
land, as opposed to a polar continent surrounded by sea) and the seasonal variation
much less, consequently much Arctic sea ice is multi-year ice, and thicker: up to 3–4
meters thick over large areas, with ridges up to 20 meters thick.

Other biomes
The Endolithic biome, consisting entirely of microscopic life in rock pores and
cracks, kilometers beneath the surface, has only recently been discovered and does
not fit well into most classification schemes.