F7- OUR EARTH IS UNIQUE

OUR EARTH

• Only planet which has a biosphere


• is an oblated sphere,


• rotates on its imaginary axis counterclockwise every 24 hours or 1 day,


• appears blue in space because it is 70% water,

Earth is unique:-

1.Has an atmosphere which is rich in oxygen (21%) and nitrogen (77%)
* presence of oxygen has made life possible on earth.
* acts as protective blanket around the earth.
* Ozone layer in the atmosphere absorbs the harmful ultraviolet radiation from the Sun & prevents it from reaching the earth.
* atmosphere absorbs terrestrial radiation & keeps earth warm during nights and winter.
* presence of atmosphere reduces extremes of temperature.

2. Has abundance of water – 70% of earth’s surface covered by ocean and seas.
* called watery planet
* layer of water is called hydrosphere.
* water is present in solid and liquid.
* water appears in gaseous state in the atmosphere also.
* water is essential for supporting plants, animals and other life forms on earth.
* water in oceans helps to moderate the temperature conditions on earth which makes the circulation of water possible.

3. Layer of rocks which form the surface of the earth is called LITHOSPHERE.
* Lithosphere provides valuable soil layer which sustains all plant life which supports the greenhouse effect
* Plants in turn support directly or indirectly all forms of life on earth
* Also provides all mineral resources needed by us.

# The combination of favourable physical environment has made Earth a HABITABLE PLANET.
# Variety & abundance of plants, animals and other forms of life make Earth unique planet.
# No life in other planets.# Various forms of life on earth constitute the BIOSPHERE
# Earth has provided an environment for the evolution of human beings and the progress of human civilization.

How did life begin?

• It is thought that life began when lightning hit the sea.


• Lightening sent energy into the water.


• Chemicals in the sea were mixed together by energy.


• New substances called amino acids were made from which life was able to grow.

AMAZING!

The first living things on earth were so small you could fit thousands of them on the head of a pin.

What were the first living things?

BACTERIA.
They lived in the sea. Some bacteria changed into alage, which were simple plants. Alage lived in the sea in masses, like huge blankets.
They made oxygen which helped to turn the sky and sea blue.

ANTIPODAL BALANCE BETWEEN LAND AND WATER

There is an anipodal balance of land and water directly opposite sides of the Earth.
1.Land on one side of the globe is balanced by water on the other side of the earth. For instance, the North Polar Arctic Ocean is opposite the Antarctic continent.
2.Northern Hemisphere is girdled by the land masses of the North America and Eurasia and Southern Hemisphere are the continents of South America, Africa and Australia
3.The landmass of Antarctica has three prominent protruding areas – one towards South America, another towards South Africa and a third towards Australia.