Earth as a Planet

Earth is known as a unique planet because it is the only planet to support life. No other planet till date is known to have life on it.

The earth is called the blue planet or watery planet because abundance of water on the earth gives it a vivid blue colour when viewed from space.

The surface of earth is made up of solid crust of rocks. The main part of the crust consists of igneous rocks, the rest consists of sedimentary and metamorphic rocks.

Venus is one of the planets that cannot support life because it is the hottest planet of the solar system. Venus is the second nearest planet to the Sun. Its atmosphere contains large amount of carbon dioxide due to which it is the hottest planet. Due to its high temperature it cannot support life.

The three factors that have made life possible on the planet earth are:

1. Its distance from the Sun is neither too near nor too far, hence ideal temperature conditions.
2. It has atmosphere containing oxygen and nitrogen necessary to support life.
3. It has water cycle. Presence of water has made existence of life possible on earth. It is essential for all kinds of life.

The various realms of the earth are — lithosphere, hydrosphere and atmosphere. Biosphere consists of all these realms along with the life.

The shape of the earth is described as an oblate spheroid because the measurements of earth at the equator and poles show that it has a slight bulge at the equator while it is slightly flattened at the poles. This shape is also known as a Geoid, meaning earth shaped.

Two proofs about the shape of the earth are:

1. All celestial bodies are spherical — Spheres are the only geometrical shapes that are circular in outline. Sun, Moon amd all other celestial bodies appear to have circular outline. Since Earth too belongs to the same system, there is no reason why Earth should be an exception.
2. Circumnavigation of the earth — Time and again people travelling round the world in different directions came back to the starting point.

The significance of the atmosphere on earth as compared to other planets are:

1. The earths atmosphere contains 21% oxygen, 78% nitrogen with traces of carbon dioxide, water vapour and other gases. This allows the existence of life on earth.
2. It extends up to 1600 km.
3. Atmosphere acts as a blanket of air protecting us from the harmful ultraviolet rays of the sun.
4. It retains the heat radiated from the earth's surface.

The conditions favourable to life on earth are:

1. The position of earth in solar system is such that it is neither too far nor too near to the sun. Hence, it receives just the right amount of heat necessary for life.
2. The atmosphere of other planets is either too thin or too dense, full of poisonous gases, making it impossible for life to exist. On the other hand, earth's atmosphere extends up to 1600 km and contains adequate amount of nitrogen (78%), oxygen (21%) and other gases like helium, carbon dioxide and water vapour.
3. It acts as a blanket, protecting us from harmful ultraviolet rays of the sun, and retains the heat radiated from the earth's surface.
4. Earth's water cycle is the most unique feature. Water is essential for the existence of life.

The planets that are made up of hard silicate rocks or metals are called Terrestrial planets. The other planets lack a solid surface. The four inner planets of the solar system- Mercury, venus, earth and Mars are terrestrial planets.

Oxygen cycle refers to the biochemical cycle which is involved in maintaining the level of oxygen in the atmosphere. Men, animals inhale oxygen and exhale carbon dioxide which is taken by plants. Plants use this carbon dioxide in photosynthesis and release oxygen, which is again used in respiration.

Earth is known as a unique planet because it is the only planet to support life. No other planet till date is known to have life on it. The presence of oxygen, water and habitable temperature enables earth to sustain life.

Water cycle refers to circulation of water from earth's surface by evaporation and transpiration to cloud formation by condensation and again falling back on earth's surface in the form of precipitation.

Biosphere refers to three realms of earth i.e. lithosphere, atmosphere and hydrosphere; along with life present on it. It is the sphere of living organisms or biological processes lying at the interfaces between atmosphere, lithosphere and hydrosphere.

The surroundings or conditions in which a person, animal or plant lives or operates is called environment. It consists of all the biotic and abiotic factors and their effects on the organism.

The envelop of air surrounding the earth is called atmosphere. The atmosphere consists of oxygen, nitrogen, carbon dioxide, argon, water vapour etc. It forms a 1600 km thick covering around the earth.

The earth is only habitable planet because of the following reasons:

1. It has habitable temperature condition.
2. It has atmosphere containing oxygen and nitrogen necessary to support life.
3. It has water in all three states.

The Earth is shaped like an orange, slightly flattened at the poles and with a bulge at the Equator. Hence, the earth's shape is Geoid. The word 'Geoid' means earth-shaped.

The earth is the home of humankind because it is the only planet which can support human life. The life exists on earth because it has the right temperature, gases like oxygen and nitrogen; and water.

Venus and Mars

21%

ecosystem

150 million km

365 1⁄4 days

Oblate spheroid

Lithification

Soil & minerals

Third

Milky Way Galaxy

Centrifugal force

Earth shaped

Below diagram shows the realms of the earth:

Below diagram shows the water cycle on the earth:

No, this belief is not true.
The Earth is not flat like a table—it is spherical in shape. This was confirmed by Ferdinand Magellan's expedition in 1519, which successfully sailed around the world, proving that the Earth is round.

Both A and R are true and R is not the correct explanation of A.

Explanation — The assertion is true because Earth's atmosphere acts like a blanket by trapping heat and maintaining the planet’s temperature, making it suitable for life. The reason is also true, as the atmosphere is made up of different gases. However, the presence of gases alone does not explain how the atmosphere acts like a blanket—it is the greenhouse effect caused by certain gases like carbon dioxide and water vapour that provides this warming effect. So, while both statements are correct, the reason does not directly explain the assertion.

Both A and R are true and R is the correct explanation of A.

Explanation — The Earth is an Oblate Spheroid — slightly flattened at the poles and with a slight bulge at the Equator. Its shape is described as "Geoid", meaning "Earth shaped".