atmosphere

• Composition of Earth's atmosphere:

  • About 80% nitrogen
  • 20% oxygen
  • Other gases like carbon dioxide, water vapor, and noble gases make up less than 1%
• Volcanic activity played a role in creating the early carbon dioxide-rich atmosphere
• Algae and plants reduced the abundance of carbon dioxide and increased the amount of oxygen in the atmosphere over time
• Early Earth's atmosphere:

  • Intense volcanic activity in the first billion years produced carbon dioxide, water vapor, nitrogen, methane, and ammonia
  • Water vapor condensed into liquid water, forming oceans
  • Carbon dioxide dissolved in the oceans, forming carbon precipitates and sediments in the seabed
• Evolution of the atmosphere:

  • Algae appeared about 2.7 billion years ago, followed by green plants
  • Algae and green plants photosynthesize, taking in carbon dioxide and producing oxygen
  • Over time, carbon dioxide levels decreased, and oxygen levels increased, allowing for the evolution of more complex life forms like animals
• Formation of sedimentary rock, oil, and gas:

  • Dead algae and plants buried in layers of sediment over millions of years
  • Sediment compressed to form sedimentary rock, oil, and gas, trapping carbon
  • Crude oil and natural gas mainly formed from dead plankton
  • Coal formed from thick deposits of dead plant material
  • Limestone mostly made of calcium carbonate from marine organisms' shells and skeletons
• Corrosion is the process by which metals are slowly broken down by reacting with substances in their environment
• Rusting is a type of corrosion where iron reacts with oxygen and water to form hydrated iron oxide, also known as rust
• At the atomic level, iron atoms lose three electrons to become iron three plus ions, while oxygen atoms gain four electrons to become oxygen two minus ions
• Rusting is a redox reaction because it involves both oxidation (iron losing electrons) and reduction (oxygen gaining electrons)
• Conditions required for rusting to take place:

  • Iron must react with both oxygen and water
  • Test tubes with iron nails:
  • First tube: water but no oxygen
  • Second tube: air (oxygen) but no water
  • Third tube: both air (oxygen) and water
  • Only the nail in the third tube will rust because it has both oxygen and water
• Corrosion affects only the surface of a metal because it's exposed to substances like water and oxygen in the environment
• Rust that forms on iron gradually flakes off, exposing new metal underneath which can also rust over time
• Aluminium forms a protective layer of aluminium oxide on the surface, preventing further corrosion of the metal
• Methods to prevent iron from rusting:

  • Barrier methods:
  • Painting
  • Oiling or greasing
  • Electroplating (using electrolysis to cover iron with a thin layer of another metal)
  • Sacrificial method:
  • Adding a more reactive metal like aluminium or zinc to the iron to prevent rusting
  • Galvanizing is an example that combines both barrier and sacrificial methods by coating iron with zinc
• Burning fossil fuels like coal, oil, and natural gas produces carbon dioxide and water when burned with plenty of oxygen in a process called complete combustion
• Incomplete combustion occurs when there is not enough oxygen available, resulting in the generation of carbon monoxide and particulates like soot
• Particulates:

  • Can get stuck in lungs when inhaled, leading to respiratory problems
  • Can form dark clouds or smog, causing global dimming by reflecting sunlight back into space
• Carbon monoxide:

  • Diffuses into the blood and binds to hemoglobin, reducing the blood's ability to carry oxygen
  • Can lead to fainting, coma, and death when oxygen transport is severely compromised
  • Colorless and odorless, making it hard to detect
• Sulfur dioxide:

  • Formed when sulfur impurities in hydrocarbons are oxidized during combustion
  • Can dissolve in clouds to form dilute sulfuric acid, leading to acid rain and damaging buildings, statues, and metals
• Nitrogen oxides:

  • Formed when nitrogen and oxygen react at high temperatures, often inside internal combustion engines
  • Can dissolve in clouds to form dilute nitric acid, causing acid rain and damaging plants by making the soil more acidic