شروط الحياة ، في الأرض والبحر .. كتاب في سبيل موسوعة علمية .. الدكتور أحمد ذكي

Conditions of life...on land and sea

The conditions for life are the same, at sea or on land.
But life, on Earth, is resourceful.
It can tolerate cold and heat... but within limits.
You can tolerate light and you can tolerate darkness... but within limits. The earth's air has pressure on the bodies of living things, and it increases and decreases, and life on earth can bear it, but within limits.
Before we talk about life in the sea, and living organisms, we must describe these conditions of life, how much of it is found in the sea, and how much is lacking.

- Heat and cold in the oceans

The sea surface temperature is close to the Earth's surface temperature. It varies depending on its location from the equator to the north and south. As you dive into the sea, you find that its temperature has decreased.
As you descend further into the water, the temperature increases slightly.
And it gets closer.
At a depth of 4,000 meters, it is almost two degrees below zero Celsius, and after that it may drop to zero Celsius, and below it, the water does not freeze, because it contains salt and great pressure.

- In the depths of the oceans, it is as quiet as the graves

The surface of the sea becomes agitated and then calms. The waves rise one day and calm down the next.
The turbulence of the sea surface reaches the bottom of this surface, and is felt to a depth of sixty meters or so, and then hardly anything is felt after that. There is an all-encompassing calm, a calm like the calm of graves.

But this does not prevent large masses from moving in the place of other large masses, due to the difference in temperature and therefore due to the difference in densities.

One of the most dangerous of these large water movements is the movement of water at the poles: the water there cools, and it contains oxygen dissolved in the air, so it falls, and in its fall goes to distant depths of water, where life needs to be supplied with oxygen, the oxygen of the air.

- And in the depths of the oceans there is a darkness worse than the darkness of the night

There is light on the surface of the sea, which is the light of the sun. You dive into the water and its light decreases, until when the adult reaches about 450 metres, all the light disappears and you can hardly feel it.
Eye .

The eye does not feel anything after that, but after that there are traces of light, which the eye does not sense, but which are affected by photographic films. It is affected even if we descend to about twice this previous depth. That is, about 900 meters from sea level.

The seas, from a depth of about 450 meters (this varies somewhat due to the clarity and turbidity of the water), are completely dark.

On the surface of the Earth there is a pressure of one atmosphere, and in the depths of the sea a thousand pressures

The air pressure above the Earth's surface is equal to the weight of a column of mercury 76 centimeters long. High school students teach this.

Based on this pressure and in harmony with it, a body was formed
Man, the animal body, and its functions.

Man tolerates the lack of pressure above the mountains, to an extent. But he cannot tolerate it on high planes where the air pressure is very low, so they provide it with air pressure that comforts travelers.

Those who search for pearls cannot bear the increase in water pressure if they go far into the water.

Professional divers wear helmets on their heads, and rubber covers on their bodies. They get air from pumps in ships above the surface of the water, and yet they cannot stay in the water for long. The farthest place under the surface of the water that a professional diver has reached is 500 feet deep, or about 150 metres.

It is common to carry compressed air in cylinders on the back of a cat, breathe through it, with a mask over his face, and then swim in the water freely, in a bathing suit. They reached depths of 300 feet, or 90 metres.

Without pressure, the diver suffers from cold.
In the modern hadith of the days, man has descended to
Far depths, but in completely closed tanks, in which a man and two men sit. They watch the sea from windows that reveal what is happening in it. But this is not the place to talk about it. Suffice it to say that with such reservoirs they reached some seabeds.

- Marine biology

We hastily, and very briefly, described the condition of the seas in that they are environments that pave the way for living things to live in.

And now we continue, hastily as well, and very briefly
Describe the life in this water.

(Illustration of the ocean, and how it descends to depths)

Life in the sea, like life on land, both have the same conditions and the same laws, and in general, the same systems prevail in them.

Plants are the origin of all food

If we talk about food, we find that all Earth's animals depend for their lives - for their food - on Earth's plants in the first place.

The earth grows plants, which are eaten by herbivorous animals, such as sheep, cows, and deer. Then come the predators, which live on meat and eat sheep, cows, and deer. This is what the wolf does, the tiger does, and the lion does. And so a person does. Man combines eating the plants of the earth with the animals of the earth who live on its plants.

Plants are the source of all food in the sea

The origin is the ear of a plant, on land, or in sea water.

The plant needs, among other things, sunlight. In the seas, plants grow and greenery abounds, in the shallow coasts, they grow in the soil of the earth under water, which makes up the shelves of the continents. The plant grows in abundance under water, in the soil of these shelves, and extends to where the sun’s light reaches deep into the water.
Then there will be darkness in the depths, and there will be no vegetation.

(Wanderers) of the seas

But all seawater contains very tiny organisms.
Some of them are microscopic, and they wander freely in the water. Some of them are included in the group of plants, and some of them are among the group of animals, and they are called plankton.

There are huge quantities of it in water.
Some of these plants rise to the surface of the seas during the day, obtain their sunshine, grow, and then descend to the surface.
The depths are good food for their inhabitants.

Then, in the depths, life is a struggle, as we described from its flow on dry land. The big one
Animals, in general, eat small ones, and small ones eat yellow ones. The strong eats the weak. The weak eats the weakest.

- Sea creatures are not all fish

And the seas are not all fish. The whale is not a fish. The seal is not a fish.

There are also crustacean animals in the sea. Such as sea fleas, known as shrimp or shrimp, which are not fish. And the gallanpo, crab, or crab, as they call it in the Levant, is not a fish.

There are also soft-bodied animals known as mollusks in the sea, such as octopuses. And so on.

For this reason, we do not say that the seas only have fish, but we say that they contain aquatic life, to combine fish and non-fish.