Stem (Earth-Science)

• Before we start learning about the Earth, it is important that we start learning about the Universe, particularly the Solar System
• The origin of the Universe is a topic that has been continuously debated on by the brilliant minds in the world of Science
• Numerous theories and hypotheses have been raised regarding how the cosmos formed
• Some were mere debunked guesses, but there are a few which caught the attention of the public due to solid evidences
• The Earth and the Solar System need to be defined in order to understand the basis of the topic
• Mankind had made numerous endeavors to explain the origin of the Earth
• In the ancient times, people tried to explain how Earth began, through myths which included gods, goddesses, and other fantastical creatures
• Creation myths


  • Greek mythology
  • Story of Leviathan in the Bible
• The creation myths have been our sole answer as to how the world and everything began
• But as developments in science are continuously made, humans started seeking the actual origin of the Earth
• Many brilliant minds have come up with different assumptions as to how the Earth and the Universe began
• Big Bang Theory


  The most widely accepted cosmological explanation of how the universe formed
• Big Bang Theory


  1. Universe started out as a single, chaotic hot mass

  2. An enormous explosion — a big bang — caused the universe to start expanding rapidly

  3. Everything, all the matter and energy in the universe, and even space itself, came out of this explosion
• While many accepts the idea of the universe originating from a small point and expanded outward, none of us have any idea what came before the Big Bang
• Evidence of Big Bang Theory

  • The galaxies are moving away from us
  • The further away a galaxy is, the faster it is moving away
• The Big Bang theory was further supported by another discovery, when scientists detected a cosmic microwave background radiation or CMBR
• This is received from all parts of the universe, and is believed to be heat left over from the original explosion
• Encounter Hypothesis


  One of the earliest theories for the formation of the planets
• Encounter Hypothesis


  1. A rogue star was said to pass close to the Sun about 5 billion years ago

  2. During this "encounter", materials which came in the form of hot gas, were tidally stripped from both the Sun and the rogue star

  3. The material fragmented into small lumps, which formed into planets
• Tidal Hypothesis


  A theory formulated by James Jeans and Harold Jeffreys, which resembles the Encounter Hypothesis on certain aspects
• Tidal Hypothesis


  1. A large nebula wandering in the space came very close to another less massive nebula, which is the sun

  2. The gravitational pull of the larger nebula caused a huge tidal upsurge of matter on the surface of the small nebula

  3. As the larger nebula moved away, matter rises from the smaller nebula and was pulled towards it

  4. The matter was then drawn to a distance where it can no longer return to the parent body, thus it was detached from the smaller nebula

  5. The matter gradually cooled down and formed the planets, including the Earth, which began to revolve around the sun
• Nebular Hypothesis


  The most accepted theory on the origin of the Solar System, also known as Kant-Laplace theory
• Nebular Hypothesis


  1. The solar system began as a cloud of dispersed particles

  2. The mutual gravitational attractions of the particles caused them to start moving and colliding, at which point chemical forces kept them bonded together

  3. Some of them became larger than others, ultimately forming the planets

  4. Laplace assumed that the Sun would start to cool, and as it does, the pressure exerted by its gases declined, caused it to contract

  5. According to the Law of Conservation of Angular Momentum, the decrease in size will cause an increase in the Sun's rotational velocity

  6. Centrifugal acceleration would push the material in the atmosphere outward, while gravitational attraction would pull it toward the central mass; when these forces balanced, a ring of material would be left behind in the plane of the Sun's equator

  7. This process goes on until materials gradually coalesced to form the planets
• Laplace's model led to the planets revolving around the Sun in the same plane and in the same direction as the Sun rotates today
• Laplace's model and the Nebular Theory became widely accepted for about a century, until the discovery of asteroids with highly eccentric orbits and moons with retrograde orbits contradicted the idea of regularity of motions in the solar system
• Another reason is that despite the Sun containing 99.9% of the mass of the solar system, the planets, particularly the four giant outer planets, carry more than 99% of the system's angular momentum
• In order for the theory to be tenable, the sun must rotate more rapidly, or the planets should be revolving around it slowly
• Protoplanet Hypothesis


  One of the current working models that are being used to learn the formation of the Solar System
• Protoplanet Hypothesis


  1. Solar systems came from rotating disks of dust coated in ice from frozen gases, which gradually form into planets

  2. The planets that form farther from the forming star tend to be bigger because the heat of the sun evaporates the gases closer to it, reducing the mass of the forming bodies