Atmosphere and Climate Notes

Changes to the Atmosphere

• Early Micro-organisms:

  • Around 3500 million years ago, micro-organisms evolved in the oceans.

  • They consumed carbon dioxide ($CO_2$) from the atmosphere.

  • They produced oxygen ($O_2$) as a byproduct of their metabolism.

• Plant Development:

  • Plants emerged on land over millions of years.

  • Plants utilize carbon dioxide to create food (glucose) through photosynthesis.

  • The photosynthesis equation is:

    $carbon \ dioxide + water \rightarrow glucose + oxygen$

• Rise of Oxygen Levels:

  • Oxygen levels in the atmosphere increased over time.

  • Evidence: Oxygen reacted with iron in rocks, forming iron oxide ($Fe<em>2O</em>3$).

  • Example: Rocks in Dallo, Ethiopia, with red iron oxide bands dating back 2.1 to 2.0 billion years.

• Reduction of Carbon Dioxide:

  • Approximately 200 million years ago, atmospheric carbon dioxide levels were significantly reduced.

  • Carbon was incorporated into the bodies and chemicals of living organisms.

• Carbon Recycling:

  • When organisms decompose, the carbon within them is released back into the environment, completing the cycle.

  • However, some organisms transform into fossil fuels (oil, coal) without decaying.

  • In fossil fuels, carbon remains trapped until combustion.

• Shell-Forming Organisms:

  • About 600 to 400 million years ago, shell-bearing organisms appeared.

  • Shells are composed of calcium carbonate ($CaCO_3$).

  • When these organisms died, their shells accumulated as sediment on the ocean floor.

  • Over time, the layers of shells compressed to create rocks like limestone, effectively locking up carbon.

Greenhouse Effect and Global Warming

• Greenhouse Effect:

  • Layers of gases in the atmosphere create the greenhouse effect, a natural process that warms the Earth.

  • Without the greenhouse effect, Earth would be much colder.

• Greenhouse Gases:

  • Key greenhouse gases include carbon dioxide, methane ($CH<em>4$), and water vapor ($H</em>2O$).

  • Increased concentrations of these gases enhance the greenhouse effect.

• Global Warming:

  • As greenhouse gas levels rise, less heat escapes the Earth's atmosphere.

  • This leads to a gradual warming of the Earth's climate, known as global warming.

• The process

  1. Energy from the sun falls on the Earth and warms it up.

  2. Some of this energy does not get through the atmosphere and is reflected back into space.

  3. Energy leaves the Earth and passes into the atmosphere.

  4. Much of this energy is reflected back to Earth by the layer of greenhouse gases such as carbon dioxide, methane and water vapour.

  5. Some of this energy from the Earth passes through the atmosphere into space.

Atmospheric Changes Today

• Analyzing Ice Cores:

  • Scientists analyze air pockets trapped in ice cores to determine past atmospheric composition.

  • Ice cores are extracted from deep layers of polar ice, formed over hundreds of thousands of years.

• Rising Carbon Dioxide Levels:

  • Until about 200 years ago, carbon dioxide levels were decreasing.

  • Since then, carbon dioxide levels have increased due to human activities.

• Fossil Fuel Combustion:

  • Humans release carbon stored in the Earth by burning fossil fuels (oil, coal) for warmth, industry, and transport.

  • The burning fossil fuels equation:

    $carbon + oxygen \rightarrow carbon \ dioxide$

• Increased Emissions:

  • Industrial development and increased transportation have led to greater emissions of carbon dioxide.

  • Power plants heavily rely on fossil fuels to generate electricity.

Deforestation and Other Human Impacts

• Deforestation:

  • The forests are cut down for wood, land for mining, palm oil production, agriculture, and pasture.

  • Deforestation reduces the number of trees available to absorb carbon dioxide through photosynthesis.

• Other Factors:

  • Cattle produce carbon dioxide and methane in their intestines.

  • The equation for the decomposition of Calcium Carbonate:

    $calcium \ carbonate \rightarrow calcium \ oxide + carbon \ dioxide$

The Atmosphere

• Definition:

  • The atmosphere is a layer of gas surrounding the Earth's surface.

  • The atmosphere's composition has changed significantly since the Earth's formation.

• Earth's Formation:

  • Earth is estimated to have formed around 4600 million years ago.

  • Initially, the Earth was molten for millions of years.

  • As it cooled, a solid crust formed.

  • Volcanic activity released gases, creating the early atmosphere.

  • Water vapor condensed into liquid water, forming lakes and oceans.

• Early Atmosphere Composition:

  • Around 4000 million years ago, the atmosphere mainly consisted of carbon dioxide, with little to no oxygen, small amounts of methane and ammonia, and some water vapor.

  • The early Earth atmosphere was similar to that of Venus today.

• Comparison with Venus:

  • Venus has a very high surface temperature of 467 °C, sufficient to melt lead.

• Gases

  • Earth's early atmosphere:

    • Water vapour

    • 95% Carbon Dioxide

    • Traces of nitrogen, ammonia, methane.

    • Average temperature above 400°C

  • Earth's atmosphere today:

    • 21% Oxygen

    • 78% Nitrogen

    • Traces of carbon dioxide, water vapour, ammonia, methane

    • Average temperature 20°C