The biosphere is made up of those parts of the earth
where life exists. The solid outer part of the earth is the
lithosphere. The atmosphere is the layer of air that extends above the
lithosphere. The earth's water-on the surface, in the ground, and in the
air makes up the hydrosphere. Since life exists on and in the ground, in
the air, and in the water, the blosphere overlaps these spheres. Although
the biosphere measures about 20 kilometers (12 mi) from top to bottom,
most life exists on and in the lithosphere and in the upper 120 meters
(400 ft) of the hydrosphere.
Origin of the Biosphere
There is evidence that the biosphere has existed
for more than three billion years. The earth's distance from the sun makes
the planet neither too hot nor too cold to support life as we know it.
Early life-forms that survived without oxygen, evolved into higher organisms
that used sunlight to make simle sugars and oxygen out of water and carbon
dioxide, a process called photosynthesis. Over a long period of time, the
atmosphere developed a mix of oxygen and other gases that would sustain
new forms of life. The energy plants receive from the sun is part of the
cycle that makes life possible.
In 1979 -- Lovelock theorizes that the earth
is a self-regulating entity unconsciously maintaining optimal conditions
for life. James Lovelock (Gaia: A New Look at Life on Earth. Oxford University
Press, 157 pp.)
Lovelock, James E.: British scientist
and naturalist is most famous for his development of the Gaia Hypothesis.
This theory suggests that life on the Earth functions like superorganism
regulating its environment through biological interactions that influence
the atmosphere, lithosphere, and hydrosphere (Lovelock, J.E., 1972, Gaia
as seen through the atmosphere. Atmos. Environment, v.6, p. 579-580)
The Gaia Hypothesis: The Gaia hypothesis
states that the temperature and composition of the Earth's surface are
actively controlled by life on the planet. It suggests that if changes
in the gas composition, temperature or oxidation state of the Earth are
induced by astronomical, biological, lithological, or other perturbations,
life responds to these changes by growth and metabolism.
published the first scientific paper suggesting the Gaia hypothesis.
The Gaia hypothesis states that the temperature and composition of the
Earth's surface are actively controlled by life on the planet. It suggests
that if changes in the gas composition, temperature or oxidation state
of the Earth are caused by extraterrestial, biological, geological, or
other disturbances, life responds to these changes by modifying the abiotic
environment through growth and metabolism. In simplier terms, biological
responses tend to regulate the state of the Earth's environment
in their favor.
for Gaia is as follows:
This theory is
to Earth Sciences for the following reasons:
If not continually
replaced by biotic activities gases like methane and hydrogen
would become non-existant in the atmosphere in a few decades.
(C02) in the Earth's atmosphere is far less abundant than chemistry alone
would allow. If life was deleted carbon dioxide would become 30 times more
abundant. Large quantities of carbon dioxide are currently locked up by
The sun's energy
output has increased by 30 % in the past 3.5 billion years. Yet, historical
climate data indicates that the temperature of the Earth has only fluctuated
by about 5° Celsius from the current average global temperature
of 15° Celsius. Computer climate models suggest that a 30 % reduction
in solar radiation would create a global average temperature of between
-10 and -52° Celsius all things being equal. These results indicate
that levels of atmospheric carbon dioxide must have been much higher
in the past when the sun was less powerful. Extra atmospheric carbon dioxide
would have created a greater greenhouse effect and warmer temperatures.
These results also indicate that some mechanism must have
removed carbon dioxide from the atmosphere as the sun's output of radiation
increased over the Earth's geologic history. This mechanism is the conversion
of atmospheric carbon dioxide into fossilized organic matter
gas, oil, coal, limestone, and
other words, Gaia!
The Gaia theory
suggests that the abiotic and biotic environment is made up of many complex
interrelationships; many of these complex interrelationships are quite
delicate and may be altered by human activity to a breaking point; and
the theory suggests that humans must learn to respect Gaia by reducing
their intentional modification of the Earth's abiotic and biotic components.