Where the world's first great civilisation was

Most of you must be aware that the Indus Valley civilisation was one of the world's first great societies. This civilisation, which developed out of farming and herding communities that carried out trade with each other, was flourishing about 4,500 years ago.

It was based in the vast river plains of what we know today as north western India and Pakistan. The two main cities - Harappa in the north of the Indus Valley and Mohenjo Daro in the south. were well planned and laid out on a grid system.

Did you know that they had not only wide roads, but also brick houses which had two storeys?

Some of the roads of Mohenjo Daro that have been excavated have revealed deep grooves made by heavily laden carts that have bean pulled by a pair of oxen.

What the 'greenhouse effect' is

The gradual heating of the Earth's atmosphere is referred to by this term by scientists who have warned that global warming would go up by about 4 per cent this year. The heating is caused mainly by carbon dioxide in the atmosphere given off by the burning of fossil fuels such as coal.

The layer of carbon dioxide acts like the glass of a greenhouse; that is, it absorbs heat radiation from the Earth and from outer space. This increasing heat 'trapped' in the atmosphere has resulted in drastic climatic changes as predicted by scientists.

Polar ice caps are already melting due to the heat. Torrential rain, floods and droughts are rampant in many parts of the world due to climatic changes.

Why birds sit on their eggs

In order for eggs to hatch, they have to be kept at just the right temperature. Sometimes, this means that parent birds must keep the eggs warm with the heat from their bodies; in warmer climates they must keep the eggs from over heating and in cooler climates, from freezing.

For example, the bird called Killdeer, which lays its eggs on rocky ground, generally shades the eggs with its outstretched wings because otherwise, the hot sun could bake the eggs. Sometimes, the bird soaks its belly in water from a nearby stream and then lowers itself over the eggs to cool them with water.

In the freezing Antarctic, father penguins hold the eggs on their feet and cover them with a flap of flesh that hangs from his abdomen to prevent the eggs from freezing. If the parent birds do so not sit on the eggs, the baby birds growing inside them will never mature and hatch.

What the major difference between the Arctic and the Antarctic is

The Arctic or the North Pole is an area much smaller than the Antarctic and consists of a frozen sea (the Arctic Ocean) ringed by frozen land.

The Antarctic, a continent of about 5,500,000 square miles (14,245,000) square kilometres), which is larger than any country in the world (except of course the former U.S.S.R.), consists entirely of ice-covered land.

What an allergy is

Most of you must be familiar with the term. Perhaps, some of you may be suffering from an allergy even at this very moment.

So, what exactly is it? It is an over-reaction of the antibodies, (the soldier cells that fight with foreign substances, germs and viruses trying to invade our bodies). Sometimes, these antibodies become 'hysterical' and cause skin rashes, swellings, coughing, sneezing and weeping to such a degree that the person virtually becomes ill.

Sometimes, allergic reactions are mild and at other times, they could be even fatal. Most often, our bodies are stuck with these over-reacting antibodies that take offence at allergens (substances that cause the violent reaction).

However, certain drugs called antihistamines help to calm down these antibodies. Regular inoculations too can help prevent allergic reactions. Staying away from the cause of the reaction also helps. Sometimes, allergies suddenly appear and disappear.

It is best to consult a physician if an allergy is frequent and bothersome.