Earth Science

• American astronomer Edwin Hubble made observations


  Late 1920s
• Hubble's observations showed that distant stars and galaxies are receding from Earth in every direction
• The velocities of recession increase in proportion with distance
• Hubble's findings imply that the Universe is expanding, as predicted by Einstein's Theory of General Relativity
• Hubble's hypothesis of an expanding universe

  1. The Universe was more condensed at a previous time

  2. All the currently observed matter and energy in the Universe were initially condensed in a very small and infinitely hot mass

  3. Suddenly, there was a big explosion-the Big Bang-discharging matter and energy in all directions

  4. The Big Bang occurred 13.8 billion years ago
• Astrophysicists have uncovered compelling evidence to support the expanding Universe as a result of the Big Bang
• By looking at light emitted by distant galaxies, scientists have found that these galaxies are rapidly moving away from the Milky Way
• The diameter of the Universe is infinite but should be at least 91 billion light-years
• The density of the Universe is 4.5 x 10-31 g/cm³
• The three most abundant elements in the Universe

  • Hydrogen
  • Helium
  • Lithium
• Galaxies


  • The building block of galaxies is the stars that are born out of clouds of gas and dust
  • Instabilities within the clouds eventually result in gravitational collapse, rotation, heating, and transformation into a protostar-the hot core of a future star as thermonuclear reactions set in
  • A galaxy is a cluster of billions of stars and clusters of galaxies form superclusters
• Formation of galaxies


  1. Stars gravitated together

  2. Formed larger and larger structures in the Universe
• Planets


  Coalesced around newly forming stars, including our own Sun
• Life took root on Earth

  3.8 billion years ago
• Components of the solar system

  • Sun
  • Eight planets
  • Dwarf planets such as Pluto
  • Satellites
  • Asteroids
  • Comets
  • Other minor bodies such as those in the Kuiper belt
  • Interplanetary dust
• Asteroid belt


  Lies between Mars and Jupiter
• Meteoroids


  Smaller asteroids, remnants of a failed planet that did not form due to disturbance from Jupiter's gravity
• The sun is the largest object in our solar system.
• An asteroid is a small rocky body orbiting the Sun within the asteroid belt between Mars and Jupiter
• A planet is an astronomical body that orbits around a star, such as the Sun
• Mercury is closest to the sun and has no atmosphere or water.
• Venus is similar to earth but hotter with thick clouds and acidic rain.
• Mars has canyons, volcanoes, and polar ice caps.
• A comet is an icy celestial body that orbits the Sun
• A dwarf planet is a celestial body that meets certain criteria but does not meet all three requirements to be classified as a full-sized planet
• A comet is a celestial body made up mostly of ice, gas, and dust
• Earth is the only known planet with life on it.
• A moon is a natural satellite that revolves around a planet
• Mars is cold and dry with dust storms and volcanoes.
• Kuiper belt


  Lies beyond Neptune (30 to 50 AU, 1 AU Sun-Earth distance = 150 million km) and comprises numerous rocky or icy bodies a few meters to hundreds of kilometers in size
• Oort cloud


  Marks the outer boundary of the solar system and is composed mostly of icy objects
• The age of the Solar System is at 4.6 billion years old based on the radioactive dating of meteorites (Solar System is much younger than the Universe)
• Milky Way galaxy


  Our solar system is located in the Milky Way galaxy, which is about 100 million light-years across (1 light year = 9.4607 × 1012 km)
• The solar system revolves around the galactic center once in about 240 million years
• All planets revolve around the Sun
• Orbits of the planets

  • Elliptical and are on the same plane
  • Much of the mass of the Solar System is concentrated at the center (Sun), while the outer planets hold angular momentum
• The periods of revolution of the planets


  Increase with increasing distance from the Sun; the innermost planet moves fastest, the outermost, the slowest
• All planets are located at regular intervals from the Sun
• Inner terrestrial planets (Mercury, Venus, Earth, and Mars)


  • Called the rocky planets, made of materials with high melting points such as silicates, iron, and nickel, rotate slower, have thin or no atmosphere, higher densities, and lower contents of volatiles - hydrogen, helium, and noble gases
• Outer four planets (Jupiter, Saturn, Uranus, and Neptune)


  • Called gas giants because of the dominance of gases and their larger size, rotate faster, have a thick atmosphere, lower densities, and fluid interiors rich in hydrogen, helium, and ices (water, ammonia, methane)