Students can go through AP State Board 9th Class Social Studies Notes Chapter 1 Our Earth to understand and remember the concept easily.
AP State Board Syllabus 9th Class Social Studies Notes Chapter 1 Our Earth
→ We human beings arrived on earth about one lakh years ago.
→ More than any other animal-human beings have been trying to make the Earth a better _ place to live in.
→ Reckless exploitation of the Earth by human beings resulted in environmental crises like global warming and poisoning of our soils, water, and air.
→ Initially, people thought that the Earth was firm and stationary and all others went around it
→ About five hundred years ago, scientists came up with a new understanding – that the Earth is not the middle of the solar system, that it is actually moved around the Sun.
→ Stars are actually part of galaxies and there are millions of galaxies in the universe.
→ The universe itself came into existence 13.7 billion years ago with a Big Bang.
→ The Earth rotates on its own axis and goes around the Sun in an orbit that is nearly circular.
→ Earth travels around the Sun at a speed of1,07,200 kilometers per hour.
→ The Earth takes 365 1/4 days to complete one revolution.
→ The Earth began to form around four and a half billion years ago and has reached its present form through several phases.
→ The Earth is made up of three main layers-crust, mantle, and core.
→ The massive supercontinent Pangaea, which existed 220 million years ago and then breaking apart into several large sections such as Laurentia and Gondwana.
→ The continents took millions of years to reach their present shape and positions on the globe.
→ We can find the latitudinal and longitudinal information of a place in a well-produced atlas or online using Google Earth.
→ With the help of the grid – a network of latitudes and longitudes we can locate places on the globe and learn much about them.
→ While latitudes are horizontal circles, the longitudes are semi-circles connecting the north pole and the south pole.
→ There are 180 latitudes and 360 longitudes.
→ The standard time of a country is the time of the meridian that passes through the center of that country.
→ The time difference between the eastern and western extremes of the country is two hours.
→ Big Bang: The single large explosion that created the universe.
→ Grid: A pattern of squares on a map that is formed of a bi-section of two latitudes and longitudes.
→ Gondwana: The break-up part of the Pangaea that consists of present South America, Africa, Madagascar, India, Arabia, Malaysia, East-Indies, Australia, and Antarctica.
→ Prime meridian: 0° longitudes is called Prime Meridian or Greenwich Meridian. It passes through Greenwich, near London.
→ Time zones: Any of the 24 regions of the globe throughout which the same standard time is used.
→ Standard time: A uniform time for places in approximately the same longitude.
→ Laurentia: The break-up part of the Pangaea that consists of present NorthEnvironmental crises: Global warming and poisoning of our soils, water, and air are called environmental crises. They are caused by the reckless exploitation of the earth by humans.
→ Global warming: Global warming is the rise in the average temperature of the Earth’s atmosphere and oceans.
→ Galaxy: Galaxies are composed of stars, dust, and dark matter all held together by gravity.
→ Universe: The totality of matter, energy, and space including the solar system, the galaxies, and continents of the space between the galaxies.
→ Solar system: The solar system is made up of all the planets that orbit the sun. In addition to planets, the solar system also consists of moons, comets, asteroids, minor planets, and dust and gas.
→ Crust: The outer layer of the earth.
→ Mantle: The layer under the crust of the earth is called the mantle.
→ Core: The third and the thickest Iayr of the earth.
→ Pangaea: The massive supercontinent that existed 220 million years ago and broke apart into several large sections – continents. (Or) America, Greenland, and all of Eurasia North of the Indian subcontinent. Pangaea is a hypothetical continent from which present continents originated by drift.
→ Tethys sea: A long shallow inland sea that separated the blocks – Laurentia and Gondwana land.
→ Latitudes: The horizontal circles that go around the earth.
→ Longitudes: The semi-circles that connect the north and south poles.
→ The crust forms only 1%of the volume of the earth, 16% consists of the mantle and 83% makes the core.
→ The thickness of the crust is just about the thickness of the shell of an egg if we assume that the size of the earth is equal to the size of an egg
→ Time and travel: You know that the earth rotates on its axis. And longitudes are imaginary lines we have made. Hence there is a difference in the time as you travel from east to west or west to east. When you are traveling West to East you gain a time of 4 minutes as you cross every longitude. But if you are traveling from East to West you lose 4 minutes as you cross every longitude. These are referred to as EGA and WLS (EGA – East Gain Add, WLS – West Lost Subtract).
→ To avoid confusion of time from place to place 82° 30’ Eastern longitude is taken as standard Meridian of India and serves as the Indian Standard Time (IST). The exact difference between Greenwich and IST is 56 hours.