The production of iron in the earths mantle is like the production of iron in extremely massive stars. Shells of nuclear fusion happen in the core of the earth which produces iron, the end product of the fusion. The abundance of iron in the earths core is due to the fact that iron has the most stable atomic nucleus in all of the elements. The mantle is full of iron and magnesium silicates. Due to the repeated partial melting of the mantle and plate tectonics, smaller ions, with +2 electric charges, cannot fit in iron and magnesium silicates in the mantle. This causes the smaller ions to leave the mantle to form earths granitic crust (Dutch).
2. According to the solar nebula theory, why is the suns equator nearly in the plane of the Earths orbit?
According to the solar nebula theory, a nebula of hot gaseous matter contracted and spun faster and faster and flattened into an equatorial ring. As the centrifugal force of the nebula exceeded the inward gravitational force, the outer most part of the nebula split from it and became a planet. The process continued and created other concentric planets. Subsequently, the central part of the nebula condensed and became the sun. The single plane created by the nebula produced the planets and the sun. They are all in a single plane (Evans).
3. Why does the solar nebula theory predict that planetary systems are common?
Solar nebula theory starts with interstellar cloud that contains hydrogen, helium, and traces of other elements. The interstellar cloud is said to be rotating. The rotating of the nebula causes fragmentation. As the solar nebula contracts, it spins faster, conserving angular momentum in the process. The solar nebula continues to grow because of the addition of particles gathered from its surroundings. Turbulences break the disk of the spinning nebula, resulting in the formulation of eddies which are many small particles. The particles combine due to an adhesive force. The nebula continues to spin and creates bigger objects that will soon become planets (Evans).
4. Why is almost every solid surface in our solar system scarred by craters?
The solar nebula theory states that as it spun continuously, the solar nebula created planets. Also, the nebula created smaller particles other than the planets. Planets that are solid-surfaced, known as terrestrial planets, were bombarded by the remaining solid particles which were also brought about by the spinning of the solar nebula. This created the craters the surfaces of these planets (Hurley-Keller).
5. If you visited some other planetary system in the act of building planets, would you expect to see the condensation sequence at work, or was it unique to our solar system?
The condensation process is expected to arise in other stars which are starting or in the early age of the protoplanet theory. Evidences are gathered with regard to the formation of circumstellar disks to some stars in our galaxy such as Vega, Formalhaut, Lyrae, and many more. Another exciting discovery is that Vega has a circumstellar disk with a radius twice the distance of Pluto from the sun (Evans).