NCERT 6th Class (CBSE) Social Science: The Realms of the Earth

Question: Describe sima sail.

Answer: The crust is made up two layers – the upper layer is called sial and the lower layer is called sima. Sial has rocks rich in silicon and aluminium while sima has silicon and magnesium. The continents have both sial and sima but the ocean floor consists of only sima.

Question: What do you understand by water cycle?

Answer: The water cycle is a constant movement of water between the earth and the atmosphere. On heating, water from the ocean turns into water vapour and rises. This process is known as evaporation. In the atmosphere. The water vapour cools and forms minute water droplets. This process is called condensation. On further cooling the tiny droplets in the clouds become bigger and fall down as rain. This process is called precipitation. precipitation helps to maintain supply of fresh water on the earth.

Question: Explain how the natural balance is disturbed in the biosphere.

Answer: The balance is disturbed in biosphere by:

1. Forest are being cut down to create space for human settlements and agriculture.
2. Oceans and seas are being over fished.
3. Increasing used of pesticides to enhance agriculture production is polluting land.
4. A large number of animal and birds are being extint due to pollution.