How Deep Is The Sea And Other Questions About The Sea - Part 1

I've always had a fascination with the sea, some of it is probably morbid, because I've also been terrified about drowning in the sea. Still, my happiest moments have been spent on the oceans and beside them in many parts of the world. Recently, I found a list of questions about the sea that I had wrote down when I was much younger. Some of the questions were my own, others were questions that my now adult children asked me. The first question is one that probably all of us have wondered at one time or another:

How Deep Is The Sea?

For all our knowledge and modern technology, we actually know very little about the depths of the sea. In fact, we actually know more about the moon than we do about the deep sea. The sea varies in depth quite as much as the land varies in height. There are slopes descending gradually from the shore and getting deeper and deeper. There are plains and tablelands that run for miles about the same depth. There are precipices with sheer descents into chasms of at least six miles deep and probably father.

Over the course of time, many charts have been prepared of the Pacific, Atlantic, and Indian oceans showing depths that were discovered at different places. In the last one hundred or so years mankind's measurements of the depth of the oceans and seas were pretty much limited. We measured by sound, by weighted rope (marked off at intervals), and by various electrical instruments. This is largely due to problems with pressure.

Generally, the average depth of all the oceans is from ten thousand to fifteen thousand feet. Of all the measurements taken in different parts of the world, only a limited number exceed great depths, though these depths of the sea correspond roughly to the great heights of the mountains above the sea, and the great sea depths are about a few miles in excess of the greatest heights on land.

There are old stories about how seaweed foretells the weather. Of course, seaweed does not foretell the state of the weather in any direct way. It merely tells us something that gives us some guidance as to the weather.

A barometer, also, does not tell us about the weather itself, but, like the seaweed, it indicates something that has to do with the weather.

As the barometer and the seaweed tell us different things, we should perhaps be able to know more about what the weather is likely to be if we used them both.

The barometer simply tells us how heavy the air is at any given time, and from that fact we can make certain guesses, more or less likely to be right, as to what will happen. The barometer tells us nothing else at all, even though we often call it a weather glass.

The seaweed tells us nothing about the pressure, or heaviness, of the air at any given time, but it tells us about the moisture of the air, and perhaps, in a way, it also tells us a little about the warmth of the air.

When a piece of seaweed feels very damp, there is a good deal of moisture in the air, rather more than the air can well carry, so that it is glad to unburden itself upon the seaweed as far as possible. Now, that means that the air may very likely unburden itself soon on a bigger scale by means of rain.

When the seaweed is dry, it means the opposite of this.

Where the sea is not too deep, life decks itself in rainbow colors. There you'll find meadows of green and blue and red algae. Blue flying fish, rosy sea anemones, red coral and mackerel in flashing hues add to the bright beauty of the undersea world. There is hardly a color on land that cannot be matched in the sea.

At great depths, in the ocean, however, the colors disappear. At seven hundred feet only a strange shade of blue is left. Half a mile down, all is complete darkness in the sea.

Yes. Large quantities of fresh water are found at certain places in the sea. Most of these places are near the mouths of large rivers which are all the time pouring fresh water into the ocean.

This fresh water may spread out over the surface for many miles. Fresh water is lighter than salt water, as you know, so it can "ride" on the top of the sea water for a time, until gradually the fresh and salt waters are mingled.

The flow of water from he Amazon River is over a million cubic feet a second. So strong is the flow that fresh water rides on the surface as far away as two hundred miles form shore.

Off the mouth of this river, many years ago, a ship saw another vessel flying signals of distress. "Water! Water! We are dying of thirst!" ran the message.

From the friendly vessel went back the advice: "Cast down your buckets where you are."

The distressed ship could not understand, and signaled again and again, always getting the same reply. At last the captain let down his buckets and up they came brimful of sparkling fresh water from the Amazon's mouth.

Fresh water can be obtained from the sea in a still more remarkable way. Much of the rain that falls in Australia sinks through the soil until it reaches a layer of rock that will not let it pass through.

The water runs along the top of this rocky layer, perhaps hundred of feet below the surface of the ground, and finally makes its way up through the sea as a submarine spring. Off the eastern coast of Australia, fresh water from these springs can be dipped up in buckets.

In the past, off some of the South Sea islands the natives dive to springs at the bottom of the sea and bring up fresh water for drinking in hollowed gourds. This is surely the most astonishing of all ways to obtain drinking water from the sea.

Ice has been seen rising to the surface of the sea off the Atlantic coast of America, coming, no doubt, from a submarine spring. As most of us know, fresh water freezes at 32 degrees Fahrenheit, while salt water does not freeze until it reaches a very much lower temperature.

Also fresh water, being lighter, floats on sea water. So the fresh water from the submarine springs freezes and floats on top of the sea water which remains liquid.

Shake a bottle of oil, perhaps the salad oil in your kitchen. Notice how slow its movements are, even though you shake quite hard.

Oil is what we call vicious liquid. Water moves much more easily, and we call it a mobile liquid.

Oil is lighter than water, so it floats on top of water. Oil poured on waves does not sink but forms a layer of sluggish, vicious liquid that lessens the splashing of the waves.

What makes a liquid viscous? It all has to do with the size of the molecules. The molecules of oil and of other viscous liquids are very large. The molecules of viscous liquids cannot be pulled apart easily, they tend to stay together.

The sun sucks up the water from the sea, but it sucks up nothing else. The salt of the sea has been brought to it by the rivers.

These, as they come down from the land, melt away from the land anything that water can melt, and this they carry into the sea. River water contains salt, too, but it contains so very little salt that we do not notice it.

Sea water is so much saltier chiefly because it contains he salt that the rivers have been carrying down to it for ages and ages.

One of the most commonest kinds of salt in sea water is ordinary salt that we use at the table, but there are a great number of other kinds too. Though table salt is the kind of salt we usually think of when we use the word, yet "salt" is really a general word for a large umber of compounds, like one another to some extent, yet different. It is the mixture of a great number of these different kinds that helps to make the sea salty.

Sand, wherever it is found, is ground up rocks. Most of this rock material is and stone, which is largely a compound of two elements, oxygen and silicon.

In the world of living things, carbon is a very common element. Silicon is one of the most common elements in the non-living world. Both silicon and carbon combine very readily with oxygen.

Ages ago, when the earth was cooling down and forming a crust, a great deal of silicon combined with oxygen in a compound that we call silica. Tiny grains of silica became glued together by means of softer substances to form stone, which we call sandstone.

This is not a very hard stone. Wind and water grind it down into grains of various sizes. Then we call it sand. Some sand comes from the breaking down of other rocks, but most of it is silica.

The tides are like great waves that travel over the surface of the oceans. As the earth spins around each twenty-four hours, the moon and sun pull upon the oceans.

At any part of the coast, the water is pulled up in a sort of heap, which we call high tide. When it is pulled away we call it low tide. When it low tide in one part of the world, the water is piling up as high tide in another part.

Take a flat pie tin with straight sides. Half fill it with water. Hold the tin steady for a moment, now tip it gently to steady for a moment, now tip it gently to the right, until the water comes up to the top of the right side.

You have high tide there, and low tide on the opposite side. Tip the tin toward the left and you see the tide going out at the right side and coming in at the left.

When we speak of a tidal wave, we do not refer to the regular flow and ebb of the tide. We have in mind the huge waves caused by violent winds or by earthquakes.

Unusually strong winds cause the waters of the ocean to come storming against the land in mighty waves. Tidal waves caused by earthquakes are even more terrible.

When an earthquake takes place under the surface of the sea, the waters above the spot are violently stirred. A great wave is then set in motion. As it sweeps along into shallow water, it destroys everything in its path. Sometimes an earthquake on the coast causes a tidal wave.

The waters near the coast are flung seaward. Then they return in a solid wall. For example, the port of Callao, in Peru, was entirely destroyed in 1746 by an earthquake and the tidal wave that followed.

The Dead Sea was first so named by the great writer Jerome because no form of animal life is found in it. This can readily be explained when we study the composition of the water.

It would, in the first place, be difficult or impossible for a fish to keep underwater -- which is as necessary for fish as it is for us to keep above water -- in the Dead Sea, so dense is the water, owing to the salt.

And, in the second place, the salts found in the water include some that are powerfully antiseptic, or fatal to life, particularly to lower forms.

The water actually contains three percent of the salt called calcium chloride, which is very poisonous to all forms of life. More than half the salt of the Dead Sea consists of magnesium chloride. Its composition is thus very different indeed from that of ordinary sea water.