Chemistry 1 Topic 1

Phase 1:

• Volcanoes gave out gases as Earth's surface was molten.
• Things cooled and a thin crust formed.
• Volcanoes gave Carbon Dioxide and Water Vapour.
• Early atmosphere was mostly CO2. Quite like Mars.
• Oceans formed when water vapour condensed

Phase 2:

• CO2 dissolved into oceans
• Marine organisms developed. When they died they were buried under layers of sediment and the CO2 became locked up in carbonate rocks.
• Green plants evolved over most of Earth, removed CO2 & produced oxygen by photosynthesis.

Phase 3:

• Build of oxygen killed off some organisms
• Oxygen created the ozone layer which blocked harmful rays from the sun.

Human activity:

• Burning fossil fuels releases CO2.
• Deforestation increases levels of CO2.
• Livestock farming releases Methane.

Volcanic activity:

• Sulfur dioxide gas reacts with sunlight, water, oxygen and dust - forming volcanic smog
• Carbon dioxide is released by volcaninc eruptions

Sources of the evolution of the atmosphere are limited:

• Learned a lot from Antartic ice cores.
• Each year, a layer of ice forms and bubbles of air get trapped inside and then buried by the next layer.
• The deeper the ice, the older the air.
• If bubbles in different layers are examined carefully you can see how the air changed.

Here's an experiment to shoow the atmosphere contains around one fifth oxygen.

• When it's heated, copper reacts with oxygen in the air to make copper (II) oxide - the reaction uses up oxygen.
• If you heat an excess of copper in a tube and pass air over it using two syringes, you can use the markers to tell you how much oxygen has been used up.
• If you start with 100cm*3 of air, you'll end up with about 80cm*3 when the reaction's finished. So about 20% of the air must be oxygen.