Session II: Population, Water Resources and Development
[15:45-17:00, March 17, 1997]
[ 9:00-11:45, March 18, 1997]
"Water, Living Things and Human"
by
Dr. Zenbei Uchijima President, Miyazaki Municipal University, Japan
Chairperson
Hon. Hao Yichun, MP (CHINA)
1. Introduction
Earth was the only planet that had water until the existence of water was
repor ted within the crest of Mars and at an Europa satellite of Jovian.
About 4.6 bi llion years ago, re-lease of heat energy from planetesimal
collision turned the primitive earth surface (which was about 1,000km deep)
into the magma ocean and the gases released from the magma ocean created
the primitive atmosphere contal ning much water vapor.
The subsequent drop in temperature caused the vapor atmosphere to lose much of
its moisture in the form of condensation and precipitation, which, in turn, cre
ated the oceans that we have today. This is considered to have occurred immedia
tely after the earth was born. The existence of large quantity of water acceler
ated the deposition of carbon di-oxlde in the earth's atmosphere in the form of
carbonate. In addition, through its excel-lent physicochemical properties, wate
r maintained the temperature of earth's surface over the range in which life ca
n survive (0 to 40℃ and functioned as an effective barrier against hazardous s
olar ultraviolet rays.
Thls led to birth of organism and subsequent evolution to create the world that
we know today. Birth of life is believed to have occurred 3.6 billion years ago
but it had spent nearly 92% of Its existence in water. In other words, biomes d
id not go ashore until 300 million years ago when hazardous ultraviolet rays wa
s weakened enough by the strato-spheric ozone layer. That is why water is calle
d "the cradle of life."
Thus, water on earth not only created life and made the environment suitable fo
r it but plays an important role as indispensable resources for development and
maintenance of modem civllization. For this reason, I would like to explain bri
efly about the relation-ship between the global environment and water resources.
2. Water on Earth
While some differences exist among researchers, the volume of water that
was sq ueezed out from the magma ocean is estimated to be in the neighborhood
of 1,373 x 106km3 , corresponding to about 2,700m
in depth when it covers the earth's su rface (IHD Commit-
