C13: The Earth's Atmosphere

What is the composition of the Earth's atmosphere today?

• Approximately 80 percent nitrogen gas.

• Approximately 20 percent oxygen gas.

• Small proportions of other gases including carbon dioxide, water vapor, and noble gases like argon.

What was the Earth's early atmosphere like and how did intense volcanic activity shape it?

• Intense volcanic activity released gases that formed the early atmosphere and oceans.

• Mainly carbon dioxide with little or no oxygen gas, similar to the atmospheres of Mars and Venus today.

• Volcanic eruptions also released nitrogen gas, water vapor, and small amounts of methane and ammonia.

How were the Earth's oceans formed?

As the Earth cooled, water vapor in the atmosphere condensed to form the oceans.

How did carbon dioxide levels in the early atmosphere decrease?

• Carbon dioxide dissolved into the newly formed oceans.

• Dissolved carbon dioxide reacted to form insoluble carbonate precipitates that settled as sedimentary rock.

• Photosynthesising organisms absorbed carbon dioxide to produce glucose and oxygen.

• Carbon became locked up in fossil fuels (coal, crude oil, natural gas) and sedimentary rocks like limestone.

How did oxygen levels in the atmosphere increase?

• Algae first evolved around 2.7 billion years ago and produced oxygen through photosynthesis.

• Over the next billion years, green plants evolved and photosynthesis steadily increased oxygen levels.

• High oxygen levels enabled land-dwelling animals to evolve.

What is the word and balanced chemical equation for photosynthesis?

• Carbon Dioxide + Water -> Glucose + Oxygen

• 6CO2 + 6H2O -> C6H12O6 + 6O2

How were coal crude oil natural gas and limestone formed?

• Coal formed from dead plant matter buried under layers of mud in swamps under high heat and pressure.

• Crude oil and natural gas formed from dead plankton deposited on sea beds, buried under mud without oxygen.

• Limestone formed from compressed marine animal skeletons and shells rich in calcium carbonate.

What are greenhouse gases and what are three key examples?

Gases in the atmosphere that maintain temperatures on Earth high enough to support life by absorbing heat, including carbon dioxide, methane, and water vapor.

How does the greenhouse effect maintain temperatures on Earth?

• Short-wavelength radiation from the sun passes through the atmosphere to warm the Earth's surface.

• The Earth radiates long-wavelength infrared radiation back out into space.

• Greenhouse gases absorb this outgoing infrared radiation and re-radiate heat in all directions back to Earth, trapping heat.

Which human activities increase carbon dioxide levels in the atmosphere?

• Burning fossil fuels in power stations, factories, and vehicles.

• Deforestation reduces the number of trees absorbing carbon dioxide via photosynthesis.

Which human activities increase methane levels in the atmosphere?

• Cattle farming and agriculture release methane during digestion.

• Landfill sites decomposing organic waste release methane.

What is global climate change and what is the scientific consensus on its cause?

An increase in average global temperatures based on peer-reviewed evidence showing that human activities are causing global warming.

What are the potential environmental consequences of global climate change?

• Melting polar ice caps and glaciers causing sea levels to rise and coastal flooding.

• Severe weather events like prolonged droughts, heatwaves, heavy rainfall, and storms.

• Loss of habitats leading to species extinction and changes in agricultural yields.

What is a carbon footprint?

The total amount of carbon dioxide and other greenhouse gases emitted over the full life cycle of a product, service, or event.

How can carbon footprints be reduced?

• Using renewable energy sources like wind, solar, and nuclear power instead of fossil fuels.

• Improving energy efficiency in homes and industries to waste less fuel.

• Implementing carbon capture and storage technologies to trap carbon emissions underground.

• Eating less meat and taxing high-emission activities.

Why is reducing carbon footprints difficult to achieve in practice?

• Economic costs of switching to green technology can hinder industrial development.

• Lack of international cooperation and agreement between governments.

• Reluctance of individuals to change personal lifestyle habits.

What atmospheric pollutants are produced by the combustion of fossil fuels?

• Carbon dioxide and carbon monoxide gas.

• Solid carbon particulates (soot) and unburned hydrocarbons.

• Sulfur dioxide gas.

• Nitrogen oxides gas (NOx).

How is toxic carbon monoxide formed and what are its hazards?

• Formed by incomplete combustion of hydrocarbon fuels due to insufficient oxygen supply.

• Toxic, colourless, and odourless gas that binds to hemoglobin in blood, reducing oxygen carrying capacity.

How are particulates soot formed and what are their hazards?

• Formed by incomplete combustion of hydrocarbons containing solid carbon particles.

• Cause respiratory health issues and damage human lungs when inhaled.

• Cause global dimming by reflecting sunlight back into space.

How is sulfur dioxide formed and what are its environmental hazards?

• Sulfur impurities in fossil fuels react with oxygen during combustion to form sulfur dioxide gas.

• Dissolves in rainwater to form acid rain, which damages buildings, trees, and aquatic life in lakes.

How are nitrogen oxides formed and what are their environmental hazards?

• High temperatures inside vehicle engines cause nitrogen and oxygen from the air to react together.

• Cause respiratory illness in humans and dissolve in rain to contribute to acid rai