Theory:

     Man has through the ages sought in vain for an imaginary elixir of life, the divine Amrita, a draught of which was thought to confer immortality. But the true elixir of life lies near our hands; for it is the commonest of all liquids, plain water! I remember one day standing on the line which separates the Libyan Desert from the Valley of the Nile in Egypt.

     On one side was visible a sea of billowing sand without a speck of green or a single living thing anywhere on it. On the other side lay one of the greatest, most fertile and densely populated areas to be found anywhere on the earth, teeming with life and vegetation. What made this wonderful difference? Why, it is the water of the river Nile flowing down to the Mediterranean from its sources a couple of thousands of miles away. Geologists tell us that the entire soil of the Nile valley is the creation of the river itself, brought down as the finest silt in its flood waters, from the highlands of Abyssinia and from remote Central Africa, and laid down through the ages in the trough through which the Nile flows into the sea. Egypt, in fact, was made by its river. Its ancient civilization was created and is sustained by the life-giving waters which come down year after year with unfailing regularity.
Explanation:
 
Humans have always searched for a magical medicine, which if drunk once, maintains all forms of life healthily; a spiritual substance which can sustain all forms of life forever. But the real cure is right in front of our eyes - the most common type of liquid substances - the humble plain water! The author recollected his experience when he had been to the Libyan desert. He stood on the line that split the Libyan desert from the Nile Valley in Egypt.
 
desert+river.jpg
The line that divides the desert from the river!
  
On one side, he saw huge waves of sand without a single green spot or any life on it. On the other side, he saw the most fertile, most occupied land on earth - swarming with people and greenery. He wondered what brought about this magnificent difference. It is due to the river Nile that flows down the Mediterranean, from a distance of \(2000\) miles. Geologists, or people who study about the constituents of earth, claim that the river itself has created the soil of the Nile valley. It has accumulated all the excellent mineral sediments from its floodwaters while flowing from the Abyssinia highlands and interiors of Central Africa. It has been sedimenting in the trenches where the river Nile flows into the sea, for hundreds of years. The author says, the country Egypt itself was created by the river Nile. It has given life to the whole civilization and sustained the livelihood in the area by its regular presence, every year.
 
nile civilaiztion.jpg
Egypt's ancient civilization was created and is sustained by the life-giving waters of Nile!
 
Meanings of difficult words:
 
No.
Words
Meanings
1
elixira magical medicine; a hypothetical substance believed to cure all illnesses
2
draughta single act of drinking or inhaling
3
vainproducing no result; useless
4
billowingcharacterized by great swelling waves or surges
5
teemingbe full of or swarming with
6
siltgranular material of a size between sand and clay, whose mineral origin is quartz and feldspar
7
troughsa channel used to convey a liquid, like trenches
Reference:
State Council of Educational Research and Training (2019). Term-2 English Standard-9. Water - The Elixir of Life - Sir C.V. Raman (pp. 121-145). Published by the Tamil Nadu Textbook and Educational Services Corporation.