In this article important points are noted from the above mentioned book topic (OUR EARTH NCERT)
ORIGIN OF EARTH (OUR EARTH NCERT)
- 1796 Immanuel Kant -Nebular Hypothesis. The hypothesis considered that the planets were formed out of a cloud of material associated with a youthful sun, which was slowly rotating.
- 1900 – Chamberlain and Moulton considered that a wandering star approached the sun. As a result, a cigar-shaped extension of material was separated from the solar surface. As the passing star moved away, the material separated from the solar surface continued to revolve around the sun and it slowly condensed into planets.
- 1920 – The most popular argument regarding the origin of the universe is the Big Bang Theory. It is also called expanding universe hypothesis. Edwin Hubble, in 1920, provided evidence that the universe is expanding. As time passes, galaxies move further and further apart.
- all matter forming the universe existed in one place in the form of a “tiny ball” (singular atom) with an unimaginably small volume, infinite temperature and infinite density.
- This tiny ball exploded violently. this resulted explosion caused expansion which is continued even present day.
- later on the temperature dropped and gave rise to atomic matter.
- The expansion of universe means increase in space between the galaxies. An alternative to this was Hoyle’s concept of steady state. It considered the universe to be roughly the same at any point of time.
THE STAR FORMATION
- Because of explosion the distribution of matter and energy was not uniform, which give rise to difference in gravitational forces and it caused the matter to get drawn together.
- The diameters of individual galaxies range from 80,000-150,000 light years. A galaxy starts to form by accumulation of hydrogen gas in the form of a very large cloud called nebula.
FORMATION OF PLANETS
- The starts are localized lumps of gas with in nebula.
- The gravitational force within the lumps leads to the formation of a core to the gas cloud and a huge rotating disc of gas and dust develops around the gas core.
- The gas cloud starts getting condensed and the matter around the core develops into small rounded objects. These small-rounded objects by the process of cohesion develop into what is called planetesimals.
- Larger bodies start forming by collision, and gravitational attraction causes the material to stick together. Planetesimals are a large number of smaller bodies.
OUR SOLAR SYSTEM
- Solar system are formed 5-5.6 billion years ago and the planets were formed about 4.6 billion years ago.
- mercury, venus, earth and mars ( first 4 are also called as Terrestrial) are called as the inner planets as they lie between the sun and the belt of asteroids the other four planets are called the outer planets.
- The rest four are called Jovian or Gas Giant planets.
- solar wind are most intense near the sun, so it blows off lot of gas and dust particle to far which results in the formation of jovian and near are solid terrestrial planets.
- It is generally believed that the formation of moon, as a satellite of the earth, is an outcome of ‘giant impact’ or what is described as “the big splat”
- Earth was having atmosphere of Hydrogen and Helium, at the begging stage. which was stripped off because of solar winds, resulting at present its chiefly contributed by nitrogen and oxygen.
- later on heavier materials started to sink towards the centre of earth and lighter ones to move towards the surface. (formation of crust and core)
Class 11 Geography Fundamental of physical Geography Chapter 2 The Origin And Evolution Of The Earth Exercise question OUR EARTH NCERT
Which one of the following figures represents the age of the earth?
(a) 4.6 million years
(b) 4.6 billion years
(c) 13.7 billion years
(d) 13.7 trillion years
ANSWER 4.6 million years
(ii) Which one of the following has the longest duration?
Which one of the following is not related to the formation or modification of the present atmosphere?
(a) Solar winds
Which one of the following represents the inner planets?
(a) Planets between the sun and the earth
(b) Planets between the sun and the belt of asteroids
(c) Planets in gaseous state
(d) Planets without satellite(s)
ANSWER Planets between the sun and the belt of asteroids