|How did the salt get into the oceans at the
beginning of their formation?
|Question Date: 1998-03-18|
The oceans get saltier due to the rivers that flow
into them. Water from the ocean evaporates, and
then rains over land and forms rivers. As the
rivers flow over the land, things like salt
dissolve into the river and are carried out to the
sea. Since the amount of water in the ocean is
more or less constant, the sea keeps picking up
more and more salt and doesn't have any place to
get rid of it. In certain places, like the Salton
Sea in California, the Great Salt Lake in Utah,
or the Dead Sea in Israel, rivers flow into lakes
that also evaporate - and the salt is concentrated
more and more over time until the salt
concentration is much higher than in the ocean -
and nothing much can live in these lakes.
The oceans formed about 4 to 4.5 billion !!!!
years ago by the eruption of volcanoes that
brought gases up to the earth's surface. Some of
these gases condensed (went from gas to liquid
state) and formed "water " to fill the low lying
areas called ocean basins. The salt of the ocean
is present because rain on the continents, or
areas that stand above sea level, dissolves rocks
a little bit as it travels eventually through the
hydrologic cycle to the oceans. Another cycle is
what happens in the middle of the ocean: there,
undersea volcanoes erupt molten lava that reacts
with sea water at high temperatures and induces
changes in the composition of the waterduring the
rock/water reaction at 400 to 500 deg C. WHY DONT
YOU CALCULATE WHAT THE TEMP IS IN DEG F EQUIVALENT
TO 400 DEG C...and then see if your oven can reach
this value of 400 C.
At any rate, the net
reaction is that Na, Ca and many other ions or
"salts" are added to sea water.
This may seem surprising, but the salt from the
ocean comes from the "fresh" water in the rivers.
In fact "fresh" water is not totally fresh (there
is even a little bit of salt in your tap water!).
The amount of salt in the rivers is very low, but
when that river water dumps into the ocean the
water evaporates and turns to clouds and rain, but
the salt stays in the water. In this way, over
hundreds of millions of years the ocean has been
gradually becoming more salty.
second part of the answer has to do with how salt
gets into the rivers. It comes from
disintegrating rock, like the granite that makes
up the Sierra Nevada, and from volcanic eruptions.
Certain minerals in granite contain small amounts
of sodium (Na). When mountains get worn down by
rivers and glaciers that sodium gets into the
rivers. Volcanic eruptions spew out a bunch of
water vapor and carbon dioxide and other gasses
like chlorine. The chlorine dissolves into the
ocean and then combines with the sodium to get
sodium chloride, or table salt.
My answer to your question has two parts. First -
It is thought that originally the only water
present on the earth was in the form of water
vapor in the atmosphere. When the atmosphere
cooled down the water vapor condensed on
atmospheric particles many of which were in the
form of salts. At a certain point these water
droplets become too heavy to remain in the
atmosphere and fall to the earth in the form of
rain. In this manner the salt particles were
leached from the atmosphere as rain and deposited
on the surface of earth. Second- As the rain
washed over the Earth's terrestrial surfaces salts
were leached from the soils where they
down streams to form the oceans. What
do you think is the primary mechanism that puts
salts into earth today? After you think about
that you can read on for the answer. Presently
the main input of new salts is from volcanic
activity that puts
salt laden materials into
the atmosphere or on the surface of the earth
where the salts are removed in the same manner as
above or by the scouring of sea.
Good question. Our oceans have been salty for a
very long time (millions of years), and it seems a
little mysterious where all that salt came from.
Part of the answer lies in the nearest little
stream. Each time it rains water runs over rocks,
and over time the water dissolves bits of the
rocks away. The water carries these dissolved
bits ("salts") down to the ocean. Although each
river does not carry
very much salt at any one
time, over the years all the bits add up.
Eventually, the slow erosion of rocks and minerals
around the world has left us with a salty ocean.
You can find out more about this process by
looking up subjects like the "water cycle" and
"erosion" in the library.
To answer your question we need to go way back
in Earth's history, over 4 billion years age,
that's 4,000,000,000 years. The early earth was a
very inhospitable place, it was likely very hot
and had lots of volcanoes. During this time, the
elements that make up the earth were
differentiating (moving around). The heavy
elements like iron and nickel moved to the center
of the earth due to the gravitational pull of the
earth. The lighter elements like silica, oxygen,
nitrogen, hydrogen and many others moves towards
the outside of the earth. Some of these elements
were gases so they became the atmosphere.
volcanic activity played an important role in
delivering these gases from deep in the earth to
the surface and into the atmosphere. One of those
gases was water vapor. Eventually the earth
cooled and the water condensed and rained down on
the earth.. The water filled up the low places
and became the oceans. The salts that are in the
oceans came from the weathering and eroding of the
the land while it was raining so much. All of the
elements like sodium, chloride, magnesium,
sulfate, silica, calcium and potassium got into
the oceans this way. This process is still going
on today but at a much slower rate. We got a good
look at it this winter with all of the erosion
that occurred in our area. Another way elements
get into the seawater is through underwater
volcanoes. These volcanoes have vents that squirt
out hot water and elements dissolved in the
The reason our oceans remain salty is
that some elements like sodium (Na+) and chloride
(Cl-) remain in the oceans a very long time. This
is called a residence time. When sodium gets put
in the ocean from rivers it takes over 200 million
years before it gets put in to sediments or
evaporite deposits (salt deposits). An eliment
like silica has a residence time of about 8,000
years, not very long. This is because silica is
used by tiny organisms called diatoms to make
their shells. When they die, they settle to the
bottom of the oceans and become sediments.
hope this answers your question. Good luck with
your science adventures!
Water washes lands and soils before to arrive to
the oceans. That wash carries salts from the
different soils and the ocean is an accumulation
basin, where over time (geological times),
evaporation concentrates these salts.
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