chapter 2 earth as planet

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lesson on geography


  • Natural Environments: The Atmosphere GE 101 Spring 2007 Boston University Myneni Lecture 03: Rotating Sphere Jan-22-07 (2 of 15) Earth as Rotating Sphere
    • Let us begin to lay the foundation for the first part of the course, which is -
    • Energy balance of the earth system
    • that is, What energy comes in, how it changes form, what goes out
    • The energy source for the earth is the sun. Therefore, we need to look at the earth-sun
    • astronomical relationship
    • We begin by looking at the earth as a Rotating, Orbiting Sphere
    • From this we will be able to answer many questions about the basic climate of the earth
    • - Why are there seasons?
    • - Why is there such a temperature difference between the equator and poles?
    • - What effect does this temperature difference have on the circulation of the
    • atmosphere and oceans
  • Earth and Moon Presented by Br. Hector Pinto INFANT JESUS SCHOOL, CHALLAKERE
    • Many speculations about the shape of the earth
    • Babylonians thought- earth was circular in shape & surrounded by river Okeanos
    • Anaximander regarded earth as cylindrical body.
    • Ancient Indians earth was flat with a huge mountain in the middle.
    • Pythogoras, Eratosthenes, Arya Bhatta & Ptlolemy earth spherical in shape
    Earth is geoid in shape
  • Nicolaus Copernicus
    • The Earth moves, in two ways.
    • It rotates on an axis (period = 1 day).
    • It revolves around the sun (period = 1 year) in same direction.
  • The Copernican Model
    • Now not a perfect sphere.
    • Flattened at the poles & bulging at the equator
    • Named geoid.
  • Our Planets At A Glance
    • Earth
    The Earth is the third closest planet to the sun and the fifth largest planet. It is small and rocky and as far as we know, the only planet that has life on it. About three quarters of the Earth's surface is covered with water and it is the only planet on which water can exist in liquid form on the surface. This is the reason that life can be sustained on it. The Earth is about 4.5 - 4.6 billion years old. It is orbited by one moon.
  • Apollo 17 view of earth
  • The Earth:
    • Only planet which has a biosphere
    • -is an oblated sphere,
    • -rotates on its imaginary
    • axis counterclockwise every
    • 24 hours or 1 day,
    • -appears blue in space
    • because it is 70% water,
  • Earth is unique:-
    • Has an atmosphere which is rich in oxygen (21%) and nitrogen (77%)
    • * presence of oxygen has made life possible on earth.
    • * acts as protective blanket around the earth.
    • * Ozone layer in the atmosphere absorbs the harmful ultraviolet radiation from the Sun & prevents it from reaching the earth.
    • * atmosphere absorbs terrestrial radiation & keeps earth warm during nights and winter.
    • * presence of atmosphere reduces extremes of temperature.
  • We breathe:
    • 78% nitrogen
    • 21% oxygen
    • 1% argon, neon, carbon dioxide, neon, & krypton
    • 2. Has abundance of water 70% of earths surface covered by ocean and seas.
    • * called watery planet
    • * layer of water is called hydrosphere.
    • * water is present in solid and liquid.
    • * water appears in gaseous state in the atmosphere also.
    • * water is essential for supporting plants, animals and other life forms on earth.
    • * water in oceans helps to moderate the temperature conditions on earth which makes the circulation of water possible.
    • Layer of rocks which form the surface of the earth is called LITHOSPHERE.
    • Lithosphere provides valuable soil layer which sustains all plant life which supports the greenhouse effect
    • Plants in turn support directly or indirectly all forms of life on earth
    • Also provides all mineral resources needed by us
    • The combination of favourable physical environment has made Earth a HABITABLE PLANET.
    • Variety & abundance of plants, animals and other forms of life make Earth unique planet.
    • No life in other planets
    • Various forms of life on earth constitute the BIOSPHERE
    • Earth has provided an environment for the evolution of human beings and the progress of human civilization
  • How did life begin?
    • It is thought that life began when lightning hit the sea.
    • Lightening sent energy into the water.
    • Chemicals in the sea were mixed together by energy.
    • New substances called amino acids were made from which life was able to grow.
    • The first living things on earth were so small you could fit thousands of them on the head of a pin.
  • What were the first living things?
    • They lived in the sea. Some bacteria changed into alage, which were simple plants. Alage lived in the sea in masses, like huge blankets.
    • They made oxygen which helped to turn the sky and sea blue.
    • There is an anipodal balance of land and water directly opposite sides of the Earth.
    • Land on one side of the globe is balanced by water on the other side of the earth. For instance, the North Polar Arctic Ocean is opposite the Antarctic continent.
    • Northern Hemisphere is girdled by the land masses of the North America and Eurasia and Southern Hemisphere are the continents of South America, Africa and Australia
    • The landmass of Antarctica has three prominent protruding areas one towards South America, another towards South Africa and a third towards Australia
    • In old days, earth was considered to be a flat disc with steep edges.
    • All heavenly bodies revolved around the Earth.
    • Aryabhatta , famous Indian astronomer, believed Earth was spherical in shape and rotated on its axis.
    • In Europe, Greek philosopher Pythagoras and Aristotle were first to state that Earth was spherical in shape. Considerable opposition to this view.
    • Now we have convincing evidence from mans landing on the Moon that the Earth is spherical in shape, the evolution of this idea may be considered briefly.
  • Proofs for shape
    • LUNAR ECLIPSE:The earth casts a shadow on the moon during a lunar eclipse. This shadow is always semi-circular in shape
    • SUNRISE AND SUNSET: The fact that the time of sunrise varies from place to place on the Earth proves that the Earth is not a flat disc.
    • If the earth was flat, all places on the earth would have sunrise and sunset at the same time.
  • Circumnavigation
    • If we travel around the earth without changing the direction, we arrive at the place we started from.
    • As the earth is spherical in shape, it is possible to circumnavigate the earth.
    • Magellans crew was first to go round the earth in a ship and complete the voyage without encountering a sharp edge.
    • Now aircrafts make many trips round the world on scheduled flights.
    • When a ship approaches the shore, a person standing on the shore can see the smoke at first and then the chimney and then the ship as a whole.
    • The photographs of the earth & other planets sent by the artificial satellites prove that the earth is round.
    • Aerial photographs from space show earth spherical. Astronauts have taken pictures of earth from moon showing its spherical shape.
    • Now not a perfect sphere.
    • Flattened at the poles & bulging at the equator
    • Named