Origins of the Earth: Evolutionary Theories in Physical Geography, Study notes of Geography

Download Origins of the Earth: Evolutionary Theories in Physical Geography and more Study notes Geography in PDF only on Docsity! FUNDAMENTALS OF PHYSICAL GEOGRAPHY UNIT-2 ORIGIN OF THE EARTH Dr. Ranju J Pandey Department of Geography Uttarakhand Open University Haldwani COURSE OUTLINE 2.1 OBJECTIVES 2.2 INTRODUCTION 2.3 THE EARTH: A MEMBER OF OUR SOLAR SYSTEM 2.4 EVOLUTIONARY THEORIES 2.4.1 GASEOUS HYPOTHESIS OF EMMANUEL KANT 2.4.2 NABULAR HYPOTHESIS OF LAPLACE 2.4.3 ELECTRO-MAGNETIC THEORY OF ALFVEN 2.5 CATACLYSMIC OR CATASTROPHIC THEORIES 2.5.1 TIDAL THEORIES OF JEANS AND JEFFREY 2.5.2 NOVA STAR HYPOTHESIS OF HOYLE AND LYTTLETON 2.5.3 INTERSTELLAR DUST HYPOTHESIS OF OTTO SCHIMIDT 2.5.4 BIG BANG THEORY 2.3 THE EARTH: A MEMBER OF OUR SOLAR SYSTEM • Solar system is a group of stars and planets. It consists of a sun and 8 planets e.g. (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune) which are round and shape like disc. Sun is also a star in our solar system. • The luminous bodies are stars and non-luminous bodies are Planets. Except Venus and Uranus the other 6 planets rotate in the same direction and their revolution around the sun. OUR SOLAR SYSTEM Source:https://int.search.myway.com/search/AJimage.jhtml?&n=7866f1d7&p2=%5EC RB%5Exdm461%5ETTABO3%5EIN&pg=AJimage&pn=1&ptb=533F1695-92D9-47D3- 8DFF- 5AOBC0580C16&qs=&si=XXXXXXXXXX&ss=sub&st=tab&trs=wtt &searchfor=image+sol artsystem&tpr=jrel2&ots=1588257277670&imgs=1p&filter=on&imgDetail=true • The distance between sun and the earth is about 149, 600,000 km (1.496x108 km). • The diameter of the earth is 12,742 km. • The average density of the earth is 5.52 respectively. • The ninth planet of the solar system is Pluto and discovered in 1930, but IAU (International Astronomical Union) relegated Pluto and recognised it as a “dwarf planet” as 134340 Pluto in month of September, year 2006. 2.4 EVOLUTIONARY THEORIES 2.4.1 Gaseous Hypothesis of Emmanuel Kant • Article entitled ‘The General Natural History and Theory of the Heaven or the Essay on the Working and Mechanical Origin of the Entire Universe’ was presented in 1755 by the German philosopher Emmanuel Kant. • Newton’s Law’ of gravitation and rotatory motion is the base of the article of Emmanuel Kant. • In the opinion of Emmanuel Kant, the hard particles were supernaturally formed and then collided with one another. • Further he considered that the collisions between particles took place because of the mutual gravitational attraction. • Heat was generated, due to this process and the original static and cold matter was converted into a rotating nebula characterised by a strong centrifugal force about its equatorial plane. • From that day forward, the successive rings of matter were thrown off, which in course of time condensed to form the planets. • The planets underwent similar spinning and throwing the matter away in the form of rings then to form the satellites. Evaluation of Emmanuel Kant theory: • His hypothesis was criticised by the scientists and considered it baseless. As he was not able to explain the source of the origin of the primordial matter, so at last it was disapproved. • Kant did not explain the source of energy to cause the random motion of cold matter, which was motionless in the initial stage. The rotatory motion can never be generated in the collision among the particles of the primordial matter. • So it is an incorrect/wrong statement of mechanism. Emmanuel Kant consideration was against the law of conservation of angular momentum that the rotatory speed of the nebula increased with the increased of its size. 2.4.2 Nebular Hypothesis of Laplace • Solar system was formed from spinning cloud of gases (nebula) is a famous concept of a French mathematician Marquis de Laplace (1796). It is only updated version of hypothesis of Emmanuel Kant. • He told that, with gradual cooling, the nebula shrank and started spinning even more rapidly. The motion of spinning caused nebula to flatten like a disk shape. • Originally, sun was a giant cloud of gases (nebula) that rotate even, was a firm belief by him. Then due to gravity and cooling the gas get’s contracted, which forced gas to rotate faster. It threw off- a rim of gas/ ring of material separate which condenses later. Several times this process would be repeated to produce all planets. The remaining ball of gas left in centre and became the sun. • In the beginning the sun was a big incandescent gaseous mass of matter. Besides the sun, there was another star named as ‘intruding star’ in the universe. • Primitive sun is smaller in size than intruding star. The primitive sun was stationary. Rotate on its axis. • Along such a path the ‘intruding star’ was moving in such a way that it is destined to come nearer to the primitive sun. • There was a great impact of the tidal force of the intruding star on primitive sun’s surface. • When the ‘intruding star’ was near about the ‘primitive sun’ its gravitational force maximized, with a giant cigar-shaped tide, length in thousands of kilometres, as a result, was created on the outer surface of the ‘primitive sun’ and ultimate huge mass of matter, cigar shaped got ejected from the primitive sun. Filament named given by Jeans to the cigar-shaped matter. • Filament was much thicker in the centre and thinner and at the end it was sharper. 9 planets of our solar system were formed due to cooling and condensation of the incandescent mass of gaseous matter of the filament was a hypothesis given by James Jeans. • The contraction of the filament led its break down in several pieces. Every piece was condensed to form one separate planet. 9 planets were formed due to this process. The filament of incandescent gaseous matter allowed bigger planets to form in its middle portion. Smaller one towards its tapering ends. The rest remaining parts of the primitive sun became our sun (hot ball of glowing gases). Formation of planets according to tidal hypothesis (Source: Physical Geography, Savindra Singh, 2011). Star Sun Star Sun Filament Modification by Jeffreys: •‘Collision hypotheses’ a concept of British scientist Harold Jeffrey presented by the modification of the original tidal hypothesis of James Jeans in 1929. He said that, before the origin of the solar system there were 3 stars in the Universe. •The 3 stars namely of which Harold Jeffrey was talking about are: 1-Primitive sun 2-Companion star 3-Intruding star (moving towards the companion star) •As a result, the intruding star collided against the ‘companion star’. Companion star was completely smashed and shattered due to head-on collision. Some shattered portions were scattered in the sky. Remaining debris started revolving around the primitive sun. From the remaining debris of the companion star the planets were formed of our solar system. • The size of companion star was of very large and later on it became supernova due to nuclear reactions. In the process of ‘nuclear fusion’, the atoms of elements that are lighter in the star combined under intense heat and pressure to form atoms of heavier elements, releasing energy in vast amount. • The companion star was consumed and it collapsed and exploded violently due to this process. Due to violent explosion, the gaseous matter come out of the companion supernova star and changed it into a circular moving disc which started revolving around the sun. • Henceforth, the disc matter became building material for the formation of future planets. Evaluation of Hoyle and Lyttleton theory: • Hoyle’s ‘supernova hypothesis’ attempts to solve the problem of angular momentum of the planets, the problem faced due to great distance between the planets and the sun and also the problem of heavier elements of the material of the planets than the sun. • But it was not able to explain the peculiar arrangement of the planets on the basis of their size, the same direction of rotation as well as the plane of revolution and the path of the planets and the lighter constituent elements of the outer circle planets of our solar system. 2.5.3 Inter-stellar dust hypothesis of Otto Schimidt • ‘Inter-Stellar Dust Hypothesis’ was proposed by a Russian scientist Otto Schimidt in 1943 to explain the complex problems of the origin and characteristics of the solar system and the earth. • Ample evidences of the presence of ‘dark matter’ in the form of ‘gas and dust cloud’ (gas and dust particles) in the universe are given by the scientific researches about the universe. • Though mode of origin of this dark matter was explained by Otto Schimidt but it may be safely assumed that these gaseous clouds and dust particles might have been formed from the matter that is coming out of the meteors and stars. • As a thought of Otto Schimidt, the sun during its ‘galactic revolution’ captured the dark matter of the universe. There is own angular momentum of dark matter of gaseous cloud and dust particles. The dark matter after being attracted by the sun during its ‘galactic revolution’ started revolving around the primitive rotating sun. 2.5.4 Big Bang theory • In 1950’s and 1960’s the Big Bang theory was postulated. Big Bang theory was validated in 1972 through considerable evidences got from Cosmic Back-ground Explorer (COBE) explains the universe’s origin and everything in it including ourselves on the basis that the universe contained many galaxies in millions of numbers. Each one galaxy having thousands of millions of stars and each star having numerous planets around it. • The galaxies moved apart from one another. The empty space between them expanded. In the beginning there was less space between the galaxies so the universe was much small. In one instant at a fixed moment in time all of the matter in universe was created. • “For fifteen billion years as universe expanded, the hot radiation in the original fireball also expanded with it, and cooled as a result.” Some 15 billion years ago it was summarised that there was a single fireball. ‘Wispy clouds of matter were already there stretching across vast distances, upwards five hundred million light years across. • As by collapse of those clouds collapsed in upon themselves, pulled together by their own gravity, they would have broken up and formed clusters of galaxies with the galaxies themselves breaking up into stars like those in Milky Way’. The stars must have been broken up to form their planets as our earth. Thank-you.