Unit 9 - Chemistry of the Atmosphere


The Evolution of the Atmosphere - Phase 1

For the first billion years the surface of the earth was covered in volcanoes that erupted and released lots of gases. This is how the early atmosphere was formed.

The early atmoshpere was probably mostly carbon dioxide with virtually no oxygen. This is quite like the atmosphere of Mars and Venus today.

Volcanic activity also released nitrogen, which built up in the atmosphere over time, as well as water vapour and small amounts of methane and ammonia.

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The Evolution of the Atmosphere - Phase 2

When the water vapour in the atmosphere condensed it formed the oceans.

Lots of carbon dioxide was removed from the early atmosphere as it dissolved in the oceans. This dissolved carbon dioxide then went through a series of reactions to form carbon precipitates that formed sediments on the seabed.

Green plants and algae evolved and absorbed some of the carbon dioxide so that they could carry out photosynthesis. ater, marine animals evolved. Their shells and skeletons contained carbonates from the oceans.

  • When plankton and marine animals die, they fall to the seabed and get buried by layers of sediment. Over millions of years, they become compressed and form sedimentary rocks, oil and gas - trapping the carbon within them and helping to keep carbon dioxide levels in the atmosphere reduced.
  • Crude Oil and Natural Gas are formed from deposits of plankton.
  • Coal is a sedimentary rock made form thick plant deposits.
  • Limestone is also a sedimentary rock. It's mostly made of calcium carbonate deposits from the shells and skeletons of marine animals.
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The Evolution of the Atmosphere - Phase 3

Green plants and algae produced oxygen by photosynthesis as well as absorbing carbon dioxide from the atmosphere. Plants use light to convert carbon dioxide and water into sugars.

Algae evolved first around 2.7 billion years ago,the over the next billion years or so green plants evolved. As oxygen levels built up in the atmosphere over time, more complex life could evolve.

Eventually around 200 million years ago, the atmosphere reached a compisition similar to what it is today: approximately 80% nitrogen, 20% oxygen and smalla mounts of other gases mainly carbon dioxide, noble gases and water vapour.

Word Equation for Photosynthesis:

       carbon dioxide + water ------> glucose + oxygen

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Greenhouse Gases

Greenhouse gases like carbon dioxide, methane and water vapour act like an insulating layer in the Earth's atmosphere.

All particles absorb certain frequencies of radiation. Greenhouse gases don't absorb the incoming short wavelengths radiation from the sun but they do absorb the long wavelength radiation that gets reflected back off the Earth. They then re-radiate it in all directions. The longwave radiation is thermal radiation so it results in the warming of the surface of the Earth.

Human activities that affect the amount of greenhouse gases:

  • deforestation
  • bruning fossil fuels
  • creating waste
  • agriculture
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Carbon Footprints

Carbon footprints are a measure of the amount of carbon dioxide and other greenhouse gases released over the full life cycle of something. That can be a service, an event or a product.

Ways of reducing Carbon Footprints:

  • Renewable energy sources or nuclear energy.
  • Using more efficient processes could conserve energy and cut waste.
  • Governments could tax companies or individuals based on the amount of greenhouse gases they emit.
  • Goverments could also put a cap on emissions of all greenhouse gases that companies make.
  • There's also technology that captures carbon doixide released by burning fossil fuels and stores it underground.
  • Advanced technologies.
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Air Pollution

Fossil fuels such as crude oil and coal contain hydrocarbons. During combustion, the carbon and hydrogen in these compounds are oxidised so that carbon dioxide and water vapour are released into the atmosphere.

When there is a plently supply of oxygen, complete comustion occurs. Whereas incomplete combustion occurs when there is a lack of oxygen avaliable. Incomplete combustion produces two harmful products which are carbon monoxide and particulates.

Carbon monoxide is dangerous because it binds to the haemoglobin in the red blood cells, this then reduces the red blood cell's capciy to carry oxygen. A lack of oxygen can lead to fainting, a coma or even death.

Particulates can lead to respiratory problems as inhaling these particles damages the lungs because they get stuck. They are aslo bad for the environment as they help reflect sunglight bck into space meaning less light reaches the earth. (Global Dimming)

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Climate Change

Increasing Carbon Dioxide is linked to climate change:

  • The Earth's temperature varies naturally, but recently the average temperature of the Earth's temperature has been increasing. Most scientists agree that the extra carbon dioxide from human activity is causing the increase and that this will lead to clmate change.

Climate Change could have dangerous consequences:

  • An increase of global temperature could lead to polar ice caps melting causing a rise in sea levels, increased flooding and coastal erosion.
  • Changes in rainfall patterns may cause some regions to get too much or too little water.
  • The frequency and severity of storms may also increase.
  • Changes in temperature and the amount of water avaliable in a habitat may affect wild species, leading to differences in their distribution.
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