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Our earth

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Introduction

earth.jpg

Our earth is the only planet known to have a life. Life is possible due to the presence of air, water and moderate temperature conditions. The earth consists of five different layered parts-atmosphere, hydrosphere, lithosphere, mantle and core. The atmosphere is the bulk of air, primarily of nitrogen and oxygen, and surrounds the surface consisting of hydrosphere and lithosphere - the water and land masses respectively. Below them, there is the mantle and core. Studying its rocks, scientists have inferred that the earth is about 4.6 billion years old. Various hypotheses have been propounded on how the earth was formed. The scientists have unraveled that the earth like other planets was formed out of the solar nebula, a disk-shaped mass of dust and gas left over from the formation of the sun. Since its birth, the earth's surface has always been changing.

Shape and size

In the solar system, our earth is the 3rdplanet which is 149.6 million km from the sun. Our earth ranks fifth among the eight planets in terms of size. It is not perfectly round but elliptical in shape. Its equatorial region is spherical and poles are flat. The total mass of the earth is 5.972 × 1024kg. Its diameter is 12,742 km and the equatorial radius is 6,371 km.

Heat distribution

Distributions of heat differ on the earth primarily according to the distance from the equator. The amount of heat decreases as we move north or south from the equator. Equatorial regions are hot as they receive direct rays. It is very cold at poles because only slanting rays reach there. But the areas with moderate latitudes between the equator and poles receive moderate rays and remain mild. The climate is also influenced by altitude. Low-lying areas have dense air so absorb more heat than those at high altitude. Temperature decreases approximately by 1° per 165 from the sea level. Distance from the sea also affects the climate of a place. The coastal areas are mild while continental areas are extreme. The coastal areas are mild while continental areas are extreme. The influence of these factors is not always balanced. Though low-lying the Siberian plain it is not hot because of its high latitudinal location (above 60°N). Similarly though at the equator, Quito in Ecuador is not hot because of its high altitude (2850 m).

Inclination, motion and seasons

inclination.jpg

Because of its round shape, only half of the earth gets the solar rays at once. The earth's motion on its axis, every twenty-four hours, causes rotation of days and nights on the two hemispheres. The earth is also inclined at an angle of 23.5° to its orbital plane. Due to such inclination, the two hemispheres are at different distance from the sun. When one hemisphere is tilted toward the sun, the other in tilted away. Only the equator in always at the same distance. Such inclination brings about differences in length of a sunshine hour and climate of the two hemispheres. You probably know the poles have a six-month day and a six-month night in a year.

The earth also moves on its orbit to go round the sun. The movement of the inclined earth on its elliptical orbit causes changes in seasons. Two opposite hemispheres experience two opposite seasons at a time. When it in summer in England. It in winter in Australia and vice-versa.

Life and Ecosystem

The earth in the wonderful home of millions of plants and creatures with many types and features. Its moderate temperate, atmosphere and abundant water have made life possible. Varied landforms and climate conditions have supported many biomes on the earth. An ecosystem has many habitat types which are linked by ecological processes. An ecosystem may be small, like the tree or a garden, or bigger like a forest, or bigger like the Himalayas or the Sahara desert, and the whole earth in one marvellous ecosystem sustaining life in a wonderful way. Many ecosystems have been undergoing damages caused by human activities.



  • Our earth is the only planet known to have a life due to the presence of air, water and moderate temperature conditions.
  • The earth consists of five different layered parts – atmosphere, hydrosphere, lithosphere, mantle and core.
  • The total mass of the earth is 5.972 × 10 24 kg.
  • The  diameter of the earth  is 12,742 km and the equatorial radius is 6,371 km.
  • The earth is inclined at an angle of 66.5° to its orbital plane.
  • Varied landforms and climate conditions have supported many biomes on the earth.
.

Very Short Questions

The temperature of a place depends upon its latitudinal extent. The low latitudinal places like the equatorial regions have high temperature whereas the high latitudinal places like polar regions have low temperature. In other words, the temperature goes on decreasing if we move to the north and the south from the equator. It happens so because on the spherical surface of the earth the central part receives direct rays of the sun but the poles only slanting ones. The direct rays are more intense, cover little area and cannot heat it well. For instance, Sri Lanka lying in low latitudes is hotter than Mongolia lying at high altitudes.

Altitude is another factor influencing the temperature on the earth. As we go up every 165 meters high, temperature decreases approximately by 1ËšC. It is resulted from the uneven density of the atmosphere. The lower layer is thicker and has more air molecules to absorb more amount of solar heat. But the upper layers are thinner and have few air molecules causing poor absorption of the solar heat. Due to this, Birgunj lying in the Terai is hotter than Kathmandu lying in the hills.

Climate of a place also depends on its distance from sea. Naturally land heats and cools faster than water. So land has higher range of temperature than water. Water keeps same temperature condition for a longer time. Thus, interior places of a continent have extreme types of temperature but coastal places have moderate type of temperature. As an example of this, Sri Lanka, though lies nearer to the equator, has moderate temperature, while Afghanistan that lie farther, has extreme temperature.

On the globe, England lies in the Northern hemisphere and Australia in the Southern Hemisphere. Because of their locations on two opposite hemispheres, they have two opposite seasons at a time. In December, the Southern Hemisphere is tilted to the sun and has summer while the Northern Hemisphere is tilted away from the sun and has winter. This is why; the English celebrate the Christmas Day (December 25) in winter while the Australians it in summer.

Both halves of the earth have day and night in rotation as the earth moves on its axis. The revolution on its orbit causes changes in seasons. Because of its inclination, two opposite hemispheres have two opposite seasons. But if it was not inclined and not moving, only a half would always have day and another always night. Similarly, there would not be change in seasons either. Even on the side of the earth facing the sun, temperature conditions would not vary from the equator to the poles.

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  • The earth in also inclined at an angle of _______ on its orbital plane.

    250
    9.50
    7.50
    23.50
  • What is the bulk of air, primarily of nitrogen and oxygen, and other gases?

    mesosphere
    lithosphere
    atmosphere
    hydrosphere
  • What is the estimated age of the earth?

    4.6 trillion years old
    4.6 million years old
    4.6 billion years old
    4.6 thousand years old
  • Poles have__

    normal day and night
    8 month day and 4 month night
    a six-month day and a six-month night in a year.
    1 year day and 1 year night
  • Earth and other planets were formed by______ , a disc-shaped mass od dust and gas left over from the formulation of the sun

    Solar nebula
    Coastal areas
    Elliptical orbit
    Quito in Ecuador
  • What is the position of the earth, according to mass, in the solar system excluding sun?

    7th
    5th
    6th
    4th
  • The total mass of the earth is

    3.29x1024 kg
    2.50x1050 kg
    7.35x1050 kg
    5.97x1024 kg
  • Earth's diameter is

    34,129 km
    19,394 km
    12,742 km
    15,675 km
  • Kathmandu is cooler than chitwan because

    Inclination motion and seasons of the places
    Kathmandu lies in higher altitude
    Because it is far away from Kathmandu
    Distribution of heat is not same in Kathmandu and chitwan
  • The earth surface is supposed to be covered by lines of

    Equator
    North Pole and South Pole
    Prime meridian
    Latitude and longitude
  • Equator divides the earth surface into

    Southern and eastern hemisphere
    Northern and southern hemisphere
    Eastern and western hemisphere
    Southern and western hemisphere
  • The prime meridian divides the earth surface into

    Southern and eastern hemisphere
    Northern and eastern hemisphere
    Eastern and western hemisphere
    Southern and western hemisphere
  • The diameter of earth is 

    12, 742 km
    8, 147 km
    10, 192 km
    11, 555 km
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