C9 Gases of the Atmosphere

Early atmosphere composition

Early Earth atmosphere (~4.6 billion years ago) likely contained mostly carbon dioxide (CO2), with little or no oxygen (O2), some water vapour (H2O), and small amounts of methane (CH4) and ammonia (NH3). Nitrogen (N2) gradually built up over time due to volcanic activity.

Current atmosphere composition

Modern atmosphere is ~78% nitrogen (N2), ~21% oxygen (O2), ~0.04% carbon dioxide (CO2), with small variable amounts of argon (Ar), water vapour (H2O), and other noble gases.

Evidence for early atmosphere

There is limited evidence for Earth's early atmosphere because it formed ~4.6 billion years ago; scientists rely on indirect evidence such as rocks, fossil records, and comparisons with other planets like Mars and Venus.

Volcanic activity early atmosphere

Intense volcanic activity released gases such as CO2, water vapour, and nitrogen, helping form the early atmosphere; water vapour later condensed to form oceans.

Oceans effect on CO2

When oceans formed, carbon dioxide dissolved in seawater and reacted to form carbonates which precipitated as sediments, removing CO2 from the atmosphere.

Mars and Venus comparison

Early Earth atmosphere may have been similar to Mars and Venus today: mostly CO2 with little or no oxygen.

Nitrogen build up

Nitrogen increased in Earth's atmosphere over time because it is relatively unreactive and was released steadily from volcanic activity while other gases were removed or used in reactions.

Methane and ammonia early atmosphere

Small amounts of methane (CH4) and ammonia (NH3) may have been present in early atmosphere but decreased over time due to reactions and lack of protection from UV light.

Photosynthesis equation

6CO2 + 6H2O → C6H12O6 + 6O2

Oxygen increase in atmosphere

Oxygen increased due to photosynthesis by algae (~2.7 billion years ago) and later plants; oxygen gradually built up in the atmosphere over billions of years enabling animal evolution.

CO2 decrease in atmosphere

Carbon dioxide decreased due to photosynthesis, dissolution in oceans, and formation of carbonate rocks (e.g. limestone) and fossil fuels (coal, oil, gas).

Formation of limestone

Limestone forms from calcium carbonate produced by shells/skeletons of marine organisms which accumulate, compact and cement into sedimentary rock over time.

Formation of coal

Coal forms from dead plant material in swampy environments that is buried, compressed and heated over millions of years under pressure.

Formation of crude oil and gas

Crude oil and natural gas form from dead marine organisms buried under sediments, decomposed without oxygen, then subjected to heat and pressure over millions of years.

Main atmospheric changes over time

Main changes: CO2 decreased significantly, O2 increased significantly, nitrogen increased and became dominant, methane and ammonia decreased; caused mainly by photosynthesis, ocean formation, and rock/fossil fuel formation.

Greenhouse gases definition

Greenhouse gases (CO2, CH4, water vapour) trap heat in Earth's atmosphere by absorbing and re-emitting infrared radiation, keeping Earth warm enough for life.

Greenhouse effect explanation

Short wavelength radiation from the Sun passes through atmosphere and heats Earth; Earth emits long wavelength infrared radiation which is absorbed and re-emitted by greenhouse gases, trapping heat.

Short vs long wavelength radiation

Short wavelength (solar) radiation passes through atmosphere easily; long wavelength (infrared) radiation is absorbed by greenhouse gases, causing heat retention.

Carbon dioxide as greenhouse gas

CO2 is a greenhouse gas that contributes to global warming by trapping infrared radiation; levels increase due to human activities like burning fossil fuels and deforestation.

Methane as greenhouse gas

Methane (CH4) is a strong greenhouse gas produced in small amounts but traps more heat per molecule than CO2; increased by agriculture and waste decomposition.

Human activities increasing CO2

CO2 increases due to burning fossil fuels (coal, oil, gas) in transport, power stations, and industry, and deforestation which reduces photosynthesis.

Human activities increasing methane

Methane increases due to cattle farming (ruminant digestion), rice paddies, landfill waste decomposition, and decomposition of organic matter without oxygen.

Global climate change evidence

Evidence includes rising global temperatures, melting ice caps, rising sea levels, and changes in weather patterns; supported by peer-reviewed scientific data but includes uncertainty due to complex systems.

Uncertainty in climate models

Climate models are simplified representations of complex systems; uncertainties arise due to incomplete data, assumptions, and difficulty predicting long-term interactions.

Peer review importance

Peer review ensures scientific work is checked by other experts for accuracy, reliability, and bias reduction before publication, improving trust in results.

Media bias climate change

Media reports may be biased or simplified, sometimes presenting incomplete evidence or focusing on selected data, which can distort scientific conclusions.

Global climate change effects

Four effects include: rising sea levels (ice melting), extreme weather events (storms, droughts), loss of biodiversity (habitat change), and changes in agriculture (crop yields affected).

Carbon footprint definition

Carbon footprint is the total amount of greenhouse gases (especially CO2 and CH4) emitted across the full life cycle of a product, service, or event.

Reducing carbon footprint

Carbon footprint can be reduced by using renewable energy, improving energy efficiency, using public transport, reducing meat consumption, recycling, and reforestation.

Limitations of carbon reduction

Actions may be limited due to cost, lack of infrastructure, reliance on fossil fuels, political decisions, and difficulty changing human behaviour.

Combustion of fuels pollutants

Burning fuels produces CO2 (complete combustion), CO (incomplete combustion), water vapour, soot (carbon particles), sulfur dioxide (if sulfur present), nitrogen oxides (at high temperatures), and particulates.

Carbon monoxide formation

Carbon monoxide forms during incomplete combustion when there is insufficient oxygen for full oxidation of carbon to carbon dioxide.

Soot formation

Soot (carbon particles) forms during incomplete combustion of hydrocarbons when fuel does not fully burn.

Sulfur dioxide formation

Sulfur dioxide forms when sulfur impurities in fuels react with oxygen during combustion.

Nitrogen oxides formation

Nitrogen oxides (NOx) form at high temperatures when nitrogen and oxygen in air react in engines or power stations.

Particulates definition

Particulates are tiny solid particles (soot, unburnt hydrocarbons) released during combustion that remain suspended in air.

Carbon monoxide properties

Carbon monoxide is colourless, odourless, toxic gas that binds to haemoglobin, reducing oxygen transport in blood.

Sulfur dioxide effects

Sulfur dioxide causes respiratory problems, irritates lungs, and contributes to acid rain which damages ecosystems and buildings.

Nitrogen oxides effects

Nitrogen oxides cause respiratory irritation and contribute to acid rain and environmental damage.

Particulates effects

Particulates cause respiratory diseases, lung damage, and global dimming by blocking sunlight reaching Earth's surface.

Acid rain formation

Acid rain forms when sulfur dioxide and nitrogen oxides react with water vapour in the atmosphere to form acidic solutions.

Global dimming definition

Global dimming is the reduction in sunlight reaching Earth's surface due to particulates reflecting and absorbing sunlight in the atmosphere.