Important Points to be remember for Revision
Natural Resources : Class 9 Science
Fossil fuels considered as non-renewable resources because it takes millions of the year for recycle.
Differential heating of earth surface [water & land] causes the wind.
Air is a bad conductor of heat, therefore atmosphere maintains the average temperature of the earth. The atmosphere prevents sudden increase in temperature during day time and during night, it prevents the escape of heat into outer space.
The envelope of air that surrounds our planet earth is called atmosphere. Different layers of atmosphere are :-
(a) Troposphere (b) Stratosphere (c) Mesosphere (d) Thermosphere
Air is inexhaustible natural resource. It is a mixture of gases such as nitrogen, Oxygen and
Carbon dioxide. It also holds water vapours & dust particles. It is essential for life.
World Environment day - 5th June : It was established by UN General Assembly in 1972.
The availability of water decides not only the number of individuals of each species that are able to survive in a particular area, but it also decides the biodiversity of life there.
Besides, the availability of water, other factors like the temperature and nature of soil play significant role in deciding the sustainability of life in a region.
The organic materials present into the soil in the form of decayed dead plant & animal matter, is called humus. Humus makes the soil more porous to allow water and air to penetrate deep in the ground & also increase water holding capacity of soil.
In terrestrial ecosystems, more than 90 percent of the moisture passes through plants by transpiration and only 10 percent evaporates directly from surfaces.