26.1-The Evolution of the Atmosphere

Phase 1-Volcanoes gave out gases

• The first billion years to Earth’s history were pretty explosive, the surface was covered om volcanoes that erupted and released lots of gases

• The early atmosphere was probably mostly carbon dioxide with virtual no oxygen

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

Phase 2-oceans, algae and green plants absorbed carbon dioxide

• 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 carbonate precipitates hat formed sediments on the seabed

• Green plants and algae evolved and absorbed some of carbon dioxide so that they could carry out photosynthesis

Phase 3-Green plants and algae produced oxygen

• As well as absorbing the carbon dioxide in the atmosphere, green plants and algae produced oxygen by photosynthesis, this is when plants use light to convert carbon dioxide and water into sugars

• Algae evolved first, about 2.7 billion years ago

• Then over the next billion green plats also evolved

• Eventually 200 million yeas ago, the atmosphere reached a composition similar to today, 78% nitrogen, 21% oxygen, 0.04% carbon dioxide

26.2-Greenhouse Gases and Climate Change

Carbon dioxide is a greenhouse gas

• 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

• They don’t absorb the incoming short wavelength radiation from the sun, but they do absorb the long wavelength radiation that gets reflected back off the Earth

• Some forms of human activity affect the amount of greenhouse gases in the atmosphere

  • Deforestation: fewer trees means less CO2 is removed from the atmosphere via photosynthesis

  • Burning fossil fuels: carbon that was locked up in these fuels is released

  • Agriculture: more farm animals produce more methane through their digestive processes

  • Creating waste: more landfill sites and more waste from agriculture means more CO2 and methane released by decomposition of waste

Increasing carbon dioxide is linked to climate change

• The Earth’s temperature varies naturally, but recently the average temperature of the Earth’s surface has been increasing

• Most scientists agree that the extra carbon dioxide from human activity is causing this increase and that this will lead to climate change

• Evidence for this has been peer-reviewed so you known that the information out there is reliable

• Unfortunately, it’s hard to fully understand the Earth’s climate, this is because it’s so complex and there are so many variables, that it’s very hard to make a model that isn’t oversimplified

• This had led to speculation, particularly in the media, where stories may be biased or only some of the information given

Practice Questions:

• Describe how carbon dioxide helps to maintain temperatures on Earth

  • Carbon dioxide allows short wavelength radiation to pass through the atmosphere to the Earth’s surface carbon dioxide absorbs outgoing long wavelength radiation which allows the Earth’s atmosphere to remain warm

• Why does the release of this carbon dioxide cause an environmental problem?

  • Because too much leads to too many long wavelengths being absorbed, meaning the Earth’s atmosphere becomes too warm

• Why is the percentage of nitrogen in the atmosphere so high?

  • Because its unreactive and therefore always remains in the atmosphere