Скачать с ютуб Geography Lecture 1 || Evolution of Earth || Ncert + GC Leong || UPSC prelims 2025 || TheIASLab в хорошем качестве

Geography Lecture 1 || Evolution of Earth || Ncert + GC Leong || UPSC prelims 2025 || TheIASLab

Pdf link- https://t.me/theIASLab This Lecture is about- THE ORIGIN AND EVOLUTION OF THE EARTH 1. Theories of Earth Origin a. Early Theories b. Modern Theories 2. Star Formation 3. Formation of Planets 4. Our Solar System 5. Earth a. Origin of Life b. Latitude c. Longitudes (Meridian) d. Standard Time e. Eclipse Early Theories of Origin of Earth The major early theories of the earth’s origin are discussed below. Nebular Hypothesis – This theory was developed by Immanuel Kant and modified in 1796 by Pierre Laplace. According to this hypothesis, the planets were formed out of a cloud of material associated with a youthful sun, which was slowly rotating. In 1900, Chamberlain and Moulton considered that a wandering star approached the sun which resulted in the formation of a cigar-shaped extension of material that got separated from the solar surface. This separated material continued to revolve around the sun and slowly got condensed into planets. The binary theories considered a companion to be coexisting with the sun. In 1950, the Nebular Hypothesis was revised by Otto Schmidt (in Russia) and Carl Weizascar (in Germany). According to them, the sun was surrounded by a solar nebula consisting mainly of hydrogen and helium along with dust. The friction and collision of particles led to the formation of a disk-shaped cloud and planets were formed through the process of accretion. Origin of Earth Modern Theories Big Bang Theory The Big Bang Theory explains the origin of the universe. It is also called the expanding universe hypothesis. In 1927, Abbe Georges Lemaitre, a Belgian astronomer was the first to provide a theory on the origin of the Universe. It was Edwin Hubble who provided evidence that the universe is expanding. According to this theory, all matter that formed the universe existed in one point (tiny ball) called singularity having an unimaginable small volume, infinite temperature and infinite density. The great event of the big bang happened some 13.7 billion years ago. The tiny ball exploded which led to a huge expansion and this expansion continues even today. There was rapid expansion within fractions of a second after the bang. Thereafter, the expansion slowed down. With the expansion some of the energy was converted into matter. Within the first three minutes from the big bang event, the first atom began to form. Within 300,000 years from the big bang, temperature dropped down to 4500 K and gave rise to atomic matter. The majority of atoms formed were hydrogen, along with helium and traces of lithium. Huge clouds of these elements fused through gravity to form stars and galaxies. Once there were two theories for explaining the origin of the universe – the Big Bang theory and the Hoyle’s concept of steady state. The steady state theory considered the universe to be roughly the same at any point of time. However, with greater evidence becoming available about the expanding universe, the Big Bang theory was confirmed which proposes that the universe originated from a single violent explosion of a very minute amount (tiny ball) of matter of high density and temperature. Evolution of the Earth The earth was a barren, rocky and hot object with a thin atmosphere of hydrogen and helium. Lithosphere – With the increasing density, the temperature inside the earth increased and the materials started getting separated depending on their densities. The heavier elements like iron moved towards the centre and lighter ones moved towards the surface. With the passage of time the earth cooled, solidified and condensed into a smaller size and formed the crust (the outer layer of the earth). The different layers of the earth starting from the surface are crust, mantle, outer core and inner core. From crust to the core, density increases. Atmosphere – The solar wind was most intense nearer the sun; so it blew off lots of gas and dust from the terrestrial planets – Mercury, Venus, Earth and Mars. During the process of cooling of earth, gases and water vapour escaped from the interior of the earth thereby starting the evolution of the present atmosphere. The early atmosphere mainly had water vapour, carbon dioxide, nitrogen, methane, ammonia and small amounts of free oxygen. The process of release of gases from the interior of the earth is called “degassing”. Hydrosphere – The frequent volcanic eruptions provided the atmosphere with water vapour and gases. With the cooling of the earth, water vapours condensed and brought rain. The carbon dioxide in the atmosphere got dissolved in rainwater which further lowered the temperature leading to more condensation and more rain. The rain water got collected into depressions to give rise to oceans. Oceans got saturated with oxygen through the process of photosynthesis and then some 2,000 million years ago oxygen began to flood the atmosphere.