>I am a Pre-K teacher and we are currently doing a unit on the ocean. What is
>the easiest way to explain to the children why the ocean is salty?
This answer provided by Diane Conradson, Field Biologist (retired), San
Jose State University, California, via www.askjeeves.com.
Until recent times, the saltiness of the ocean was believed to have come
from the weathering and erosion of continental rocks. If this were true,
then the chemical composition of river water and salty inland lakes should
be similar to that of the oceans. But river water salts are largely calcium
and bicarbonate ions, while seawater salts are largely sodium and chloride,
which forms sodium chloride, or table salt.
The upper mantle layer of the Earth has more of the minerals found in sea
water, and in similar proportions. So deep sea vents, rift vents, and
volcanoes actually supply most of the salts through outgassing. The
weathered rocks supply sodium ions; the outgassing supplies chloride ions.
Mid-ocean rifts supply much of the sea's calcium, as the heat from the
rifts dissolves sea floor rocks.
The ratio of each mineral in sea water to the total percentage of dissolved
solids remains a constant. So whether the sodium chloride is taken from a
salt pond or the middle of the ocean, its ratio to the other salts remains
the same. Sea water contains less silica (quartz) and calcium than river
water, however, because marine plants and animals remove them to form their
hard parts (shells, cases, and tests).
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