The substance to which our planet owes its existence

When an astronomer trains his tele­scope at one of the planets neighboring the Earth, he always wonders about the presence of water and oxygen there. His interest is quite natural: should they exist in any quantity on the planet life there might be expected somehow to resemble ours. It is water that brought our Earth into existence, developed it to its present state, and created life. Above all else, wa­ter is the most wonderful substance on the Earth and the more we learn about it the more we marvel at it.

Hardly anybody has ever speculates on the remarkable properties of water, and no wonder: we encounter water every­where, it is a common thing on our planet. Three quarters of the Earth's surface is covered by water, with about one fifth of the land covered by solidified water (ice and snow); clouds of water vapour and tiny drops of water always shroud a good half of that land, where there are no clouds water-vapour is always present in the air. That's how common water is on our planet: it constitutes as much as seventy-one per cent of the human body. And common things are never regarded as wonderful. Its very commonplaceness. However, is extraordinary. No other sub­stances is more abundant on the Earth and none occurs in three states at the same time: solid, liquid and gaseous.

Water has conditioned the Earth's cli­mate. But for water our planet would have cooled long ago and all life would have disappeared.Water possesses a high heat capacity.When warmed it absorbs much heat, and cooling it loses it. Oceans, seas and all other reservoirs on our planet, as well as atmospheric vapour act as heat ac­cumulators: in warm weather they absorb heat, and when it is cold they give it off, so warming the air and all surrounding space.

The cold of outer space would long ago have penetrated the Earth but for its warm coat. This coat is the atmosphere which surrounds our planet, the water va­pour acting like a layer of cotton wool. Over deserts where water vapour is scarce the coat is full of holes. Thus unprotected the Earth is fiercely heated by the Sun in the daytime and cools off completely over­night. That is why temperature fluctua­tions in the desert are so great.

Nonetheless the Earth would freeze in the long run if it were not for another of water's remarkable properties. It is com­mon knowledge that almost all substances contract on cooling, but water expands. If it contracted, ice would be heavier than water and would sink. All the water would gradually turn into ice and the Earth would be left with a very light mantle of a gaseous atmosphere containing no water vapour.

Water has one more extraordinary characteristic: its latent heat of melting and evaporation is extremely high, it is only due to this that life is possible in a hot climate. Only by evaporating water (i.e. giving off a large amount of heat) can animals and men maintain their body temperature several degrees lower than that of the ambient atmosphere.

The role of water in nature is unique because life would be impossible without it. Life originated in primeval seas from the substances dissolved in them. Ever since then chemical reactions have been occurring in every cell of all animals and plants between the dissolved substances.

Perhaps the least known among the remarkable properties of water is its abil­ity to form an extremely strong surface film resulting from the very powerful mu­tual attraction of molecules in the upper­most layers. Its surface tension is strong enough to support things which seemingly should not float.

The sharks of today are one of the most biologically curious and least studied groups of vertebrates. They are hard to observe in their native habitat and some of their species are very rare, many of them are very large in size which makes their investigation difficult. What is more, sharks are sometimes so bold as to attack people. The reasons for such behav­iour have not been adequately studied as yet, and the means of defence against an attacking shark are ineffectual.

For centuries these animals have been connected with various legends and myths, which occasionally have some foundation but frequently are the fruits of people's imagination.

At the same time, sharks have long been hunted: their meat is used for food; their teeth for making knives, battle swords or surgical scalpels, the most re­cent application being to make souvenirs. The shark skin makes excellent material for craftsmen, the fat is a most valuable raw material for the medical and pharma­ceutical industries.

Systematic study of sharks is rela­tively recent development, which began as late as the 1940s. However, in spite of considerable progress in investigations, these animals are still a puzzle and many of their biological features lead the scien­tists into a blind alley. What is most curi­ous is that in popular literature and occa­sionally scientific research, one out of every three or four communications is ei­ther out-of-date «sensation», or just an error. And it is all this that made me take my pen and try to summarize the materi­als I have collected in the past two dec­ades as well as the findings of research voyages and expeditions to the North At­lantic, the Black Sea, the Sea of Japan, the Sea of Okhotsk, the coastal waters of Cuba and Indonesia.

The paleontological chronicles allow us to trace history of sharks back more than 350 million years (man's history is almost 100 times shorter). Throughout a long period sharks have always lived alongside people, competing with man for food in the ocean and occasionally killing one another.

COMING SOON: AN ASTEROID

This announcement has recently been made at the Chair of Astronomy of Kiev University to inform us that the near fu­ture will see the closest approach of our planet to a large asteroid. The announce­ment came just when astronomers at Kiev University were getting ready to launch a station to track comets and carry out vari­ous radio-astronomical observations. Its two observation towers, accommodating a series of laboratories, have been erected on a high hill near Kiev. It was a mere chance that the installation and testing of the two telescopes delivered from Lenin­grad coincided with the time of the «great opposition» with Eros, which moves in an elliptical orbit. This planet was discovered last century and named after the mytho­logical god of love.

The astronomical catalogues list over 1, 800 asteroids. Why, then, is that out of this impressive list of «minor planets» Eros should merit the keen attention of astronomers? It is because of its very un­usual orbit and because it differs from most other asteroids in that its brightness is variable. An analysis of variations inEros' brightness to be made during this period of maximum approach will enable its outline to be more accurately determined and thus give better information on the origin of the «flying stones», which are broken pieces from giant planet surfaces.

The investigations are expected to be carried out under very favorable circum­stances: after the 20th of January 1975 Eros will be at its closest to the Earth slightly over 20 million kilometers. This rare occasion was last observed in 1931 but at that time the conditions for obser­vation were unfavorable. This time it will be different and even the amateur as­tronomer will be able to see Eros with the aid of prismatic field-glasses. Besides, the Kiev astronomers will have a chance to test new optical instruments under real conditions and develop methods of track­ing minor celestial bodies in space. They will also have the opportunity of continu­ing work on a theoretical interpretation of Eros' configuration which still offers some riddles.

Ответьте на вопросы по тексту:

1. What brought our Earth into existence, developed it to its present state, and created life?

2. What part of the Earth's surface is covered by water?

3.What is the role of water on the Earth?

4. What planet was discovered last century and named after the mytho­logical god of love?

5. How many asteroids do astronomical catalogues list?

6. When was Eros at its closest to the Earth slightly over 20 million kilometers

7. When was this rare occasion last observed?