The biosphere is the global sum of all ecosystems. It
can also be termed the zone of life on Earth, a closed system (apart from solar and cosmic radiation
and heat from the interior of the Earth), and largely self-regulating. By the
most general biophysiological definition, the biosphere is the
global ecological
system integrating all living beings and their relationships, including their
interaction with the elements of the lithosphere,
hydrosphere,
and atmosphere. The biosphere is postulated to have evolved,
beginning with a process of biopoesis
(life created naturally from non-living matter such as simple organic
compounds) or biogenesis (life created from living matter), at least
some 3.5 billion years ago. The earliest evidences for life on
Earth are graphite
found to be biogenic in 3.7 billion-year-old metasedimentary
rocks discovered in Western Greenland and microbial
mat fossils
found in 3.48 billion-year-old sandstone discovered in Western
Australia.
In a general sense, biospheres are any closed,
self-regulating systems containing ecosystems; including artificial ones such
as Biosphere
2 and BIOS-3;
and, potentially, ones on other planets or moons.
Origin and use of the term
The term "biosphere" was coined by geologist Eduard
Suess in 1875, which he defined as:
The place on Earth's surface where life dwells.
While this concept has a geological origin, it is an
indication of the effect of both Charles
Darwin and Matthew F. Maury on the Earth
sciences. The biosphere's ecological context comes from the 1920s (see
Vladimir I. Vernadsky), preceding the 1935
introduction of the term "ecosystem" by Sir Arthur
Tansley (see ecology history). Vernadsky defined ecology as the
science of the biosphere. It is an interdisciplinary
concept for integrating astronomy, geophysics, meteorology,
biogeography,
evolution,
geology, geochemistry,
hydrology
and, generally speaking, all life and Earth sciences.
Narrow definition
Geochemists define the biosphere as being the total sum of
living organisms (the "biomass" or "biota"
as referred to by biologists and ecologists). In this sense, the biosphere is
but one of four separate components of the geochemical model, the other three
being lithosphere,
hydrosphere,
and atmosphere. The word ecosphere,
coined during the 1960s, encompasses both biological and physical components of
the planet.
The Second International Conference on Closed Life Systems
defined biospherics as the science and technology of analogs and models of Earth's biosphere;
i.e., artificial Earth-like biospheres. Others may include the creation of
artificial non-Earth biospheres—for example, human-centered biospheres or a
native Martian
biosphere—as part of the topic of biospherics.
Gaia hypothesis
During the early 1970s, the British chemist James
Lovelock and Lynn Margulis, a microbiologist from the United
States, added to the hypothesis, specifically noting the ties between the
biosphere and other Earth systems. For example, when carbon
dioxide amounts increase in the atmosphere, plants grow more quickly. As
their growth continues, they remove more and more carbon dioxide from the
atmosphere.
Many scientists are now involved with new topics of study
that examine interactions between biotic and abiotic factors in the biosphere,
such as geobiology
and geomicrobiology.
Ecosystems occur when communities and their physical
environment work together as a system. The difference between this and a
biosphere is simple—the biosphere is everything in general terms.
Extent of Earth's biosphere
Every part of the planet, from the polar
ice caps to the equator,
features life of some kind. 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 difficult to measure. Birds typically fly at altitudes of 650 to
1,800 metres, and fish that live deep underwater can be found down to -8,372
metres 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 metres; bar-headed geese migrate at altitudes of at least
8,300 metres; yaks
live at elevations between 3,200 to 5,400 metres above sea level; mountain
goats live up to 3,050 metres. Herbivorous animals at these elevations
depend on lichens, grasses, and herbs.
Microscopic organisms live at such extremes that, taking
them into consideration, the thickness of the biosphere is much greater.
Culturable microbes have been found in the Earth's upper atmosphere as high as
41 km (25 mi) (Wainwright et al., 2003, in FEMS Microbiology
Letters). It is unlikely, however, that microbes are active at such altitudes,
where temperatures and air pressure are extremely minor and ultraviolet radiation very intense. More
likely, these microbes were brought into the upper atmosphere by winds or
possibly volcanic eruptions. Barophilic
marine microbes have been found at more than 10 km (6 mi) depth in
the Mariana
Trench (Takamia et al., 1997, in FEMS Microbiology Letters).In fact,
single-celled life forms have been found in the deepest part of the Mariana
Trench, Challenger Deep, at depths of 36,201 feet (11,034 meters).Microbes are
not limited to the air, water or the Earth's surface. Culturable thermophilic
microbes have been extracted from cores drilled more than 5 km (3 mi)
into the Earth's crust in Sweden, from rocks between
65-75 °C.
Temperature increases with increasing depth into the Earth's
crust. The rate at which the temperature increases depends on many factors,
including type of crust (continental vs. oceanic), rock type, geographic
location, etc. The greatest known temperature at which microbial life can exist
is 122 °C (Methanopyrus kandleri Strain 116), and it
is likely that the limit of life in the "deep biosphere" is defined
by temperature rather than absolute depth.
Our biosphere is divided into a number of biomes, inhabited by
fairly 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 populous biomes lie near the equator.
Terrestrial organisms in temperate and Arctic biomes have relatively small
amounts of total biomass, smaller energy requirements, and display prominent
adaptations to cold, including world-spanning migrations, social adaptations, homeothermy,
estivation
and multiple layers of insulation.
Specific biospheres
For this list, if a word is followed by a number, it is
usually referring to a specific system or number. Thus:
- Biosphere 1, the planet Earth.
- Biosphere 2, laboratory in Arizona, United States, which contains 3.15 acres (13,000 m²) of closed ecosystem.
- BIOS-3, a closed ecosystem at the Institute of Biophysics in Krasnoyarsk, Siberia, in what was then the Soviet Union.
- Biosphere J (CEEF, Closed Ecology Experiment Facilities), an experiment in Japan.[12][13]
Extraterrestrial biospheres
No biospheres have been detected beyond the Earth;
therefore, the existence of extraterrestrial biospheres remains hypothetical.
The rare Earth hypothesis suggests they should be
very rare, save ones composed of microbial life only. On the other hand, new research suggests
that Earth
analogs may be quite numerous, at least in the Milky Way
galaxy. Given limited understanding of abiogenesis,
it is currently unknown what percentage of these planets actually develop
biospheres.
It is also possible that artificial biospheres will be
created during the future, for example on Mars.
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