environment, encompasses all living and non-living things
occurring naturally on Earth or some region thereof. It is
an environment that encompasses the interaction of all
living species. The concept of the natural environment
can be distinguished by components:
* Complete ecological units that function as natural
systems without massive human intervention, including all
vegetation, microorganisms, soil, rocks, atmosphere and
natural phenomena that occur within their boundaries.
* Universal natural resources and physical phenomena that
lack clear-cut boundaries, such as air, water, and climate,
as well as energy, radiation, electric charge, and
magnetism, not originating from human activity.
The natural environment is contrasted with the built
environment, which comprises the areas and components that
are strongly influenced by humans. A geographical area is
regarded as a natural environment (with an indefinite
article), if the human impact on it is kept under a certain
Earth science generally recognizes 4 spheres, the
lithosphere, the hydrosphere, the atmosphere, and the
biosphere as correspondent to rocks, water, air, and life.
Some scientists include, as part of the spheres of the
Earth, the cryosphere (corresponding to ice) as a distinct
portion of the hydrosphere, as well as the pedosphere
(corresponding to soil) as an active and intermixed sphere.
Earth science (also known as geoscience, the geosciences
or the Earth Sciences), is an all-embracing term for the
sciences related to the planet Earth. There are four major
disciplines in earth sciences, namely geography, geology,
geophysics and geodesy. These major disciplines use physics,
chemistry, biology, chronology and mathematics to build a
qualitative and quantitative understanding of the principal
areas or spheres of the Earth system.
The Earth's crust, or lithosphere, is the outermost solid
surface of the planet and is chemically and mechanically
different from underlying mantle. It has been generated
largely by igneous processes in which magma (molten rock)
cools and solidifies to form solid rock. Beneath the
lithosphere lies the mantle which is heated by the decay of
radioactive elements. The mantle though solid is in a state
of rheic convection. This convection process causes the
lithospheric plates to move, albeit slowly. The resulting
process is known as plate tectonics. Volcanoes result
primarily from the melting of subducted crust material or of
rising mantle at mid-ocean ridges and mantle plumes.
It is the common understanding of natural environment
that underlies environmentalism — a broad political, social,
and philosophical movement that advocates various actions
and policies in the interest of protecting what nature
remains in the natural environment, or restoring or
expanding the role of nature in this environment. While true
wilderness is increasingly rare, wild nature (e.g.,
unmanaged forests, uncultivated grasslands, wildlife,
wildflowers) can be found in many locations previously
inhabited by humans.
Evidence suggests that life on Earth
has existed for about 3.7 billion years. All known life
forms share fundamental molecular mechanisms, and based on
these observations, theories on the origin of life attempt
to find a mechanism explaining the formation of a primordial
single cell organism from which all life originates. There
are many different hypotheses regarding the path that might
have been taken from simple organic molecules via
pre-cellular life to protocells and metabolism.
Although there is no universal agreement on the
definition of life, scientists generally accept that the
biological manifestation of life is characterized by
organization, metabolism, growth, adaptation, response to
stimuli and reproduction. Life may also be said to be
simply the characteristic state of organisms. In biology,
the science of living organisms, "life" is the condition
which distinguishes active organisms from inorganic matter,
including the capacity for growth, functional activity and
the continual change preceding death.