Where do the oceans get their salt from?
How does the salt get into the sea?
Anyone who has swallowed water while bathing in the sea knows from their own experience: Sea water tastes salty. And when the water evaporates, a fine white layer of salt often sticks to the skin. This is because, on average, seawater consists of 3.5 percent salt. For one liter of sea water that is 35 grams or about one and a half heaped tablespoons of salt. But how does the salt actually get into the sea?
Many of these salts come from the rocks of the earth's crust. Rainwater dissolves salts from the rock and takes them with it. It washes them into rivers and into the groundwater. This is how salts are washed into the sea. Because relatively little salt is transported, the river water is hardly salty. Only in the sea does the concentration increase. Because there are also salts from the ocean floor and submarine volcanoes. When the sea water evaporates, all of these salts are left behind. That is why washed-out salts have been accumulating in the oceans for millions of years.
The salinity is not the same in all seas. The more water evaporates, the more salty the water becomes. The Red Sea contains more salt than the Pacific. And the Dead Sea in the Middle East - actually a lake - is so salty with a salt content of around 30 percent that you can lie in it without sinking. The Baltic Sea, on the other hand, is rather poor in salt: because of the low temperature, very little water evaporates there. In addition, many rivers flow into the inland sea and feed it with fresh water. That is why the Baltic Sea is much less salty than the Dead Sea.
Singapore is not poor in water. On the contrary: it is surrounded by the sea. But what the city of 5 million does not need salty sea water. Drinkable fresh water is in demand. That is why the city-state built a huge dam for its water supplies: "Marina Barrage"!
So far, Singapore has bought almost all of its drinking water from neighboring Malaysia. From there, millions of liters flowed into the city every day. But Singapore wants to make itself independent from Malaysia, because the relationship is tense. For this reason, the city began building a gigantic dam wall in 2005. A 350 meter long reinforced concrete dam now shields the Singapore River from the open sea. Nine movable gates control the water level. Huge pumps can transport the water masses into the sea in the event of a storm surge or tropical precipitation. Behind the huge “Marina Barrage” wall, a freshwater lake has arisen in the middle of the city. Even if the water is still brackish and salty at the moment: From 2015 the “Marina Reservoir” reservoir will provide clean drinking water.
Marina Reservoir and the accessible Marina Barrage dam have become a tourist attraction. The residents of Singapore also use the site in their free time. But only electrically powered boats are allowed to travel on the lake. After all, in the future it should help to quench the tremendous thirst of an entire city.
No land in sight
Nowhere in the world are you further from the mainland than at Point Nemo. That is why it is also called the water pole or pole of inaccessibility. Point Nemo is located in the middle of the Pacific Ocean between Chile and New Zealand. It is exactly 2,688.22 kilometers away from Easter Island, Ducie Island and Maher Island. If you want to visit Point Nemo, you should remember its coordinates: 48 ° 52.6 'South and 123 ° 23.6' West. However, if you approach it, you will find nothing but water!
The blue planet
Seen from space, the globe appears in a strong blue. This is because almost three quarters of the earth is covered with water. Small amounts of water are transparent, but from a certain depth onwards it becomes more and more blue. Because we see the mighty oceans blue, the earth is also called "the blue planet". The term south of the equator is particularly applicable. Because the southern hemisphere is almost completely covered by the sea, because a large part of the continents have migrated to the north due to plate movement.
The vast oceans contain almost all of the water on earth. There is a lot of salt dissolved in sea water, which is why it is not suitable as drinking water. The little fresh water on earth is frozen mainly in glaciers and ice caps. Only a tiny fraction of freshwater is found in groundwater, in lakes and rivers, or in the air.
But the view from the outside is deceptive: the earth's surface is largely covered by water, but measured by the diameter of the earth, the oceans are only a very thin layer. Therefore, the water makes up only a fraction of the earth's mass. For comparison: if the earth were the size of a basketball, all the water on earth would fit into a table tennis ball. And the drinking water would be proportionally even smaller than a single popcorn.
The water cycle
The water on earth is always on the move. Huge amounts of it are constantly moving - between sea, air and land - in an eternal cycle in which not a single drop is lost.
The motor of the water cycle is the sun: It heats the water of the seas, lakes and rivers so much that it evaporates. Plants also release water vapor into the atmosphere through tiny openings. The humid air rises, tiny water droplets gather in the air and form clouds. As rain, hail or snow, the water falls back into the sea or onto the earth. If it falls on the ground, it seeps into the ground, supplies plants or flows through the ground, over streams and rivers back into the sea. The eternal cycle of evaporation, precipitation and runoff starts all over again.
The water cycle has been around for almost as long as the earth has existed. He ensures that living beings on our planet are supplied with fresh water. And not only that: Without the water cycle, the weather as we know it would not exist.
From rock to grain of sand - weathering
Today the north of Canada is a gently undulating landscape. However, many millions of years ago there was a mountain range here. In fact, even high mountains can turn into small hills over a very long period of time.
The reason for this transformation: The rock on the earth's surface is constantly exposed to wind and weather. For example, if water penetrates into cracks in the stone and freezes, it splits the stone apart. This process is called frost blasting. The rock also becomes brittle through temperature changes between day and night and through the power of water and wind. In other words: it weathers. This process can also be observed on buildings or on stone figures. During the weathering, the rock breaks down into smaller and smaller components up to fine grains of sand and dust. Different rocks weather at different rates: Granite, for example, is much more resistant than the comparatively loose sandstone.
Some types of rock even completely dissolve when they come into contact with water, for example rock salt and lime. Rock salt is chemically the same as table salt - and that already dissolves in ordinary water. Lime is a little more stable, but limestone also dissolves in acidic water. Acid is formed, for example, when rainwater in the air reacts with the gas carbon dioxide. This “acid rain” attacks the limestone and dissolves it over time. The weathering leaves rugged limestone landscapes on the surface of the earth, and caves are formed below the surface.
But not only solution weathering, heat and pressure also wear down and crumble rock under the earth's surface. Wherever plants grow, roots dig in, break up the rock piece by piece and also ensure that it is removed millimeter by millimeter.
In this way, weathering not only works on individual rocks, it gnaws at entire mountain ranges. It will take a few million years for the Black Forest to be as flat as northern Canada.
How sweet is fresh water?
It doesn't taste sweet at all, but it's called fresh water. In contrast to salt water, it contains no or only very small amounts of salt and therefore has hardly any taste. For this reason it is also well suited for the production of drinking water.
Fresh water is rare: only two to three percent of all water on earth is fresh water. Most of it is in the high mountains and at both poles. There it is stored as ice in glaciers. Only a very small fraction of the fresh water on earth flows in streams and rivers or splashes in lakes and groundwater. The water in clouds and precipitation is also "sweet".
Fresh water is vital to us. To stay healthy, a person needs about two liters of fluids per day; without water it can only survive five to seven days. In addition, we need a large amount of fresh water for showering, washing clothes or washing dishes. Plants and animals that we feed on also live from water. Freshwater is even a habitat for many living things: crayfish, pond and river mussels and freshwater fish such as trout, pikeperch and char.
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