SCI111- FINAL

• Endogenic processes


  Processes that originate from within the Earth
• Processes that contributed to the Earth's internal heat energy

  • Gravitational contraction of the Earth's interior
  • Radioactive decay of unstable isotopes
• Gravitational contraction

  Heat from the conversion of gravitational energy into heat energy as the Earth contracted into a smaller volume
• Formation of the Earth


  1. Small pieces of matter left over from the formation of the sun began colliding and sticking together due to gravity

  2. Accretionary process led to an increasingly greater gravitational attraction, forcing the Earth to contract into a smaller volume

  3. Increased compaction resulted in the conversion of gravitational energy into heat energy enough to melt matter

  4. Relatively dense elements like iron and nickel sank towards the center

  5. Less-dense elements stayed closer to the Earth's surface

  6. Earth cooled, allowing the outermost and denser material to solidify forming the crust
• Heat conducts very slowly through rocks, so the rapid build-up of this heat source within the Earth was not accommodated by an equally rapid loss of heat through the surface
• The current theory on the formation of Earth called the core accretion model states that the Earth started forming around 6 billion years ago
• Radioactive elements


  Inherently unstable, breaking down over time into more stable forms
• Radioactive decay


  1. Unstable isotope decays to more stable form

  2. Releases heat as a by-product
• Long-lived isotopes that continuously produce heat over time

  • Potassium-40 (K40)
  • Thorium-232 (Th232)
  • Uranium-235 (U235)
  • Uranium-238 (U238)
• Earth's interior hasn't cooled much over billions of years

  • Because it is insulated by the overlying material
  • Because of the radioactive decay of elements in its interior
• Radioactive decay causes collisions on an atomic scale and is continuously happening, up to this date
• These particles from radioactive nuclei collide with surrounding material, which generates heat
• Igneous rocks


  Form when melted rock cools
• Magma


  Melted rock that originates within the Earth
• Partial melting


  1. Only some of the minerals within a rock melt

  2. Happens because different minerals have different melting temperatures
• The magma that is produced by partial melting is less dense than the surrounding rock
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  Moving magma carries heat with it, and some of that heat is transferred to surrounding rocks
• If the melting temperature of a rock is less then the temperature of the magma


  The rock will begin to melt, and the composition of the magma may change to reflect a mixture of sources
• Decompression melting


  1. Melting due to a decrease in pressure

  2. The decrease in pressure affecting a hot mantle rock at a constant temperature allows melting that forms magma
• Earth's mantle is almost entirely solid rock, despite temperatures that would cause rock at Earth's surface to melt
• Mantle rock remains solid at those temperatures because the rock is 'under high pressure
• Decompression melting


  Melting triggered by a reduction in pressure
• Pressure reduction


  1. Mantle rocks move upward due to convection

  2. Mantle rocks rise as a plume within the mantle

  3. Crust thins, such as along rift zones
• Addition of Volatiles


  1. Volatiles are elements or compounds with low boiling points

  2. When volatiles mix with hot, dry rocks, the volatiles decrease the rock's melting-point and help break the chemical bonds in the rock to allow melting

  3. An example of a volatile is water
• The addition of water into the system


  Has a significant effect on the net melting temperature of rocks
• Magma


  A thick flowing substance formed when rocks below the Earth's surface melt due to extreme temperatures
• Magma formation and eruption


  1. Magma forms in chambers as it is lighter than solid rock

  2. Magma pushes through vents, fissures, and volcanoes to the Earth's surface

  3. Magma that has erupted is called lava
• Volcanism


  • Result of a planet losing its internal heat
  • Volcanoes form where rock near the surface becomes hot enough to melt
• Volcano formation at plate boundaries

  1. At mid-ocean volcanic ridges, material from Earth's interior slowly rises, melts when it reaches lower pressures and fills in the gap

  2. At subduction zones, chambers of magma may form and feed the volcanic islands
• Earth is said to be cooling because of volcanism, as volcanic eruptions are one way for Earth to lose heat
• Explosivity of volcanic eruptions

  • Depends on the composition of the magma
  • Low silica content magma is thin and runny, allowing gases to escape easily, resulting in lava flows
  • High silica content magma is thick and sticky, trapping gases which build up pressure and explode violently, blasting magma into the air as tephra
• Lava flows rarely kill people as they move slowly enough for people to get out of their way
• Explosive eruptions are more dangerous and deadly than lava flows, as volcanic ash can suffocate living organisms and hot lava mixing with water can form lahars that bury communities
• Warning signs of an impending volcanic eruption

  • Rumbling sounds
  • Volcanic tremors
  • Change in color of stream emission
  • Crater glow
  • Ground swelling
  • Localized landslides
  • Increased temperature of springs, wells, or drying up of springs/wells
  • More gas in the lava
• Metamorphism


  Changes in mineral assemblage and texture that result from subjecting a rock to different conditions of pressure, temperature, and chemical environment than those under which the rock originally formed
• Metamorphic rocks


  • Have different mineral assemblages and different textures from their parent rocks
  • May have the same overall composition as their parent rocks
• Metamorphism occurs because


  1. Minerals are only stable within a specified temperature, pressure, and chemical environment

  2. When temperature and pressure increase above the normal range for the minerals, they become unstable

  3. This causes the minerals within rocks to decompose or change into another mineral without necessarily changing the composition
• Textural changes in metamorphism

  • Minerals in parent rocks may grow larger, shrink, and change shape
  • Fossiliferous texture of limestone is destroyed when transformed into marble
  • Most metamorphic rocks have a foliated texture caused by a preferred orientation of minerals with sheet-like structures to the stress being applied
• Examples of foliated metamorphic rocks

  • Slate
  • Phyllite
  • Schist
  • Gneiss
• Mineral composition of a metamorphic rock

  Influenced by the mineral composition of the parent rock, and the amount of heat and pressure during metamorphism