other sources; however, limits must be placed on the coverage in an individual
chapter. This is just one part of humans learning to control their environment without
destroying it.
2 Special Features of Water and Their Relationship to Life
on Earth
Water is an unusual substance. It has many physical and chemical properties that do
not follow the normally expected trends. Scientists have been able to explain them.
However, this does not make them any less special.
The observation of the peculiar properties of water dates back at least as far as
L. J. Henderson [1], in 1912, in which he describes the properties of water that are
most important. First of all was that 3/4 of the earth’s surface is covered by water and
that, if it were not for the mountains of land, the entire earth would be covered by
4 kilometers (2.5 miles) deep of water.
Chemically, water is very stable; very few substances react directly with it,
although many reactions take place within it. Perhaps its thermal properties are the
most anomalous properties of water. The first of these is its specific heat or heat
capacity. Water is the standard, having been assigned a value of 1.000 in the range of
0–1
C. This is a relatively high value and enables water to maintain a relatively
constant temperature. It is important in the stabilization of biological and chemical
reactions in the aquatic environment and serves to moderate the earth’s climate by
providing a reservoir of heat in the tropical oceans and a reservoir of cold in the polar
ice caps. These effects in turn help aquatic organisms maintain a constant temperature and reduce the amount of heat regulation necessary for mammals.
A second important thermal property is water’s latent heat of fusion and vaporization. The latent heat of fusion, 88 cal/g, is quite high. The latent heat of vaporization, 536 cal/g, is the highest known for any substance. The latent heats represent
the amount of heat that must be provided to a given weight of water to convert it
from either the solid to the liquid or the liquid to the vapor state at the same
temperature. This is very important in the evaporation of water and represents a
large transfer of energy from the tropical oceans, where energy is available to
evaporate the water, and this energy is released elsewhere on the earth in the form
of condensation. The latter effect is also very important since it regulates or
moderates temperatures throughout the world, preventing the tropics from becoming
excessively hot and the poles extremely cold. It is similarly important in physiological heat regulation, in terms of both perspiration in animals and transpiration in
plants.
The thermal conductivity of a substance represents the time rate of transfer of heat
by conduction through a unit thickness across a unit area for a unit of temperature in
a unit of time. The value for water of 0.0125 cal/s-cm-cm
2 -
C is quite high compared
to other liquids. Ice, however, has a higher thermal conductivity, which results in a
lake’s more rapid cooling once the first layer of ice has formed.
234
D. B. Aulenbach et al.
chapter. This is just one part of humans learning to control their environment without
destroying it.
2 Special Features of Water and Their Relationship to Life
on Earth
Water is an unusual substance. It has many physical and chemical properties that do
not follow the normally expected trends. Scientists have been able to explain them.
However, this does not make them any less special.
The observation of the peculiar properties of water dates back at least as far as
L. J. Henderson [1], in 1912, in which he describes the properties of water that are
most important. First of all was that 3/4 of the earth’s surface is covered by water and
that, if it were not for the mountains of land, the entire earth would be covered by
4 kilometers (2.5 miles) deep of water.
Chemically, water is very stable; very few substances react directly with it,
although many reactions take place within it. Perhaps its thermal properties are the
most anomalous properties of water. The first of these is its specific heat or heat
capacity. Water is the standard, having been assigned a value of 1.000 in the range of
0–1
C. This is a relatively high value and enables water to maintain a relatively
constant temperature. It is important in the stabilization of biological and chemical
reactions in the aquatic environment and serves to moderate the earth’s climate by
providing a reservoir of heat in the tropical oceans and a reservoir of cold in the polar
ice caps. These effects in turn help aquatic organisms maintain a constant temperature and reduce the amount of heat regulation necessary for mammals.
A second important thermal property is water’s latent heat of fusion and vaporization. The latent heat of fusion, 88 cal/g, is quite high. The latent heat of vaporization, 536 cal/g, is the highest known for any substance. The latent heats represent
the amount of heat that must be provided to a given weight of water to convert it
from either the solid to the liquid or the liquid to the vapor state at the same
temperature. This is very important in the evaporation of water and represents a
large transfer of energy from the tropical oceans, where energy is available to
evaporate the water, and this energy is released elsewhere on the earth in the form
of condensation. The latter effect is also very important since it regulates or
moderates temperatures throughout the world, preventing the tropics from becoming
excessively hot and the poles extremely cold. It is similarly important in physiological heat regulation, in terms of both perspiration in animals and transpiration in
plants.
The thermal conductivity of a substance represents the time rate of transfer of heat
by conduction through a unit thickness across a unit area for a unit of temperature in
a unit of time. The value for water of 0.0125 cal/s-cm-cm
2 -
C is quite high compared
to other liquids. Ice, however, has a higher thermal conductivity, which results in a
lake’s more rapid cooling once the first layer of ice has formed.
234
D. B. Aulenbach et al.