Evolution of the Earth's Atmosphere, Greenhouse Effect & Pollutants

1

Phase 1: The Early Volcanic Atmosphere (First Billion Years)

Intense volcanic activity released gases that formed the early atmosphere: mainly carbon dioxide (CO₂), with little or no oxygen (O₂), much like Mars and Venus today. Volcanoes also released water vapour (which condensed as the Earth cooled to form the oceans), nitrogen (N₂, which gradually built up because it is unreactive), and small proportions of methane (CH₄) and ammonia (NH₃).

Save

2

Phase 2: Decreasing CO₂ & Increasing O₂

When the oceans formed, CO₂ dissolved in the water and carbonate precipitates formed sediments on the seabed. Around 2.7 billion years ago, photosynthetic algae evolved (followed by plants over the next billion years): 6CO₂ + 6H₂O -> C₆H₁₂O₆ + 6O₂. This decreased atmospheric CO₂ and steadily increased O₂, eventually allowing complex animals to evolve.

Save

3

Modern Atmosphere Composition

For the last 200 million years, the proportions of gases in the atmosphere have been roughly constant: approximately 80% Nitrogen (N₂, 78%), 20% Oxygen (O₂, 21%), and small proportions of noble gases (mainly Argon, ~0.9%), Carbon Dioxide (~0.04%), and water vapour.

Save

4

The Greenhouse Effect & Climate Change

Greenhouse gases (water vapour, carbon dioxide, and methane) maintain temperatures on Earth high enough to support life. Short-wavelength radiation from the Sun passes through the atmosphere; the Earth's surface absorbs it and re-emits longer-wavelength infrared (IR) radiation, which is absorbed by greenhouse gas molecules. Human activities (burning fossil fuels, deforestation, cattle farming, rice paddies, landfill waste) increase CO₂ and CH₄, enhancing the greenhouse effect and causing global climate change.

Save

5

Carbon Footprints

The carbon footprint is the total amount of carbon dioxide and other greenhouse gases emitted over the full life cycle of a product, service, or event. It can be reduced by using renewable energy resources, carbon capture and storage (CCS, pumping CO₂ deep underground into porous rock), eating less beef, improving insulation, and taxing emissions.

Save

6

Atmospheric Pollutants from Combustion

1. Carbon dioxide (CO₂): greenhouse gas causing global warming. 2. Carbon monoxide (CO): toxic, colourless, odourless gas from incomplete combustion. 3. Soot / Carbon particulates (C): from incomplete combustion of diesel; causes global dimming and respiratory lung damage. 4. Sulfur dioxide (SO₂): from oxidising sulfur impurities in fuels; causes acid rain. 5. Nitrogen oxides (NOₓ): from N₂ + O₂ reacting in hot car engines; causes respiratory issues and acid rain.

Save

1. Q1

   Earth's early atmosphere was ~95% carbon dioxide, whereas today's atmosphere contains only 0.04% carbon dioxide. Describe in detail the geological and biological processes that caused this massive decrease in atmospheric carbon dioxide. [6 marks]

   Check Mark Scheme

   Click “Check Mark Scheme” to compare your answer, 1. As the Earth cooled, water vapour in the early volcanic atmosphere condensed to form the oceans [1 mark]. 2. Large quantities of atmospheric carbon dioxide dissolved directly into the ocean water [1 mark]. 3. Dissolved carbon dioxide reacted with metal ions in seawater to form insoluble carbonate precipitates (calcium carbonate), which settled on the seabed as limestone sedimentary rock [1 mark]. 4. Around 2.7 billion years ago, photosynthetic algae evolved, followed later by green plants, which absorbed carbon dioxide from the atmosphere for photosynthesis [1 mark]. 5. Marine animals used dissolved carbonates to build shells and skeletons; when they died, their remains were compacted on the seabed to form more limestone rock [1 mark]. 6. Dead plants and marine plankton that were buried in anaerobic conditions (mud/swamps) were compressed over millions of years, locking carbon away in fossil fuels (coal, crude oil, and natural gas) [1 mark].

2. Q2

   Explain how greenhouse gases maintain the temperature of the Earth, and describe three potential consequences of global climate change caused by rising greenhouse gas concentrations. [6 marks]

   Check Mark Scheme

   Click “Check Mark Scheme” to compare your answer, 1. Short-wavelength electromagnetic radiation (visible light and UV) from the Sun passes through the Earth's atmosphere without being absorbed by greenhouse gases [1 mark]. 2. The Earth's surface absorbs this solar radiation, warms up, and re-emits thermal energy back towards space as longer-wavelength infrared (IR) radiation [1 mark]. 3. Greenhouse gas molecules (CO₂, CH₄, H₂O) absorb this outgoing long-wavelength infrared radiation and re-radiate it back towards the Earth, keeping the lower atmosphere warm [1 mark]. 4. Consequence 1: Melting of polar ice caps and glaciers combined with thermal expansion of seawater causes sea levels to rise, flooding low-lying coastal land [1 mark]. 5. Consequence 2: More frequent, severe, and unpredictable extreme weather events (such as droughts, heatwaves, hurricanes, and heavy flooding) [1 mark]. 6. Consequence 3: Changes in temperature and rainfall distribution alter habitats and migration patterns, leading to crop failures (food insecurity) and species extinction [1 mark].

3. Q3

   Explain how burning fossil fuels in power stations and car engines leads to the formation of acid rain, and state two harmful effects of acid rain. [4 marks]

   Check Mark Scheme

   Click “Check Mark Scheme” to compare your answer, 1. Fossil fuels (especially coal) contain sulfur impurities; when burned, the sulfur is oxidised to form sulfur dioxide gas (S + O₂ -> SO₂) [1 mark]. 2. Inside hot car engines, high temperatures cause nitrogen and oxygen from the air to react, forming oxides of nitrogen (NOₓ) [1 mark]. 3. Sulfur dioxide and nitrogen oxides dissolve in water droplets in clouds and react with oxygen to form dilute sulfuric acid and nitric acid, which fall as acid rain [1 mark]. 4. Harmful effects: Acid rain acidifies lakes and rivers (killing fish and aquatic life), damages trees and soil nutrients, and corrodes limestone buildings and metal structures [1 mark].

4. Q4

   Define the term 'carbon footprint', give two ways an individual can reduce their carbon footprint, and explain two reasons why it is difficult to reduce carbon footprints globally. [4 marks]

   Check Mark Scheme

   Click “Check Mark Scheme” to compare your answer, 1. Definition: The total amount of carbon dioxide and other greenhouse gases emitted over the full life cycle of a product, service, or event [1 mark]. 2. Individual actions: Walk/cycle or use public transport/electric vehicles instead of petrol cars; insulate homes and use renewable electricity; or eat less beef/dairy [1 mark]. 3. Difficulty 1: Renewable energy technologies and Carbon Capture and Storage (CCS) are expensive to build, and businesses/consumers resist higher energy costs or taxes [1 mark]. 4. Difficulty 2: It is difficult to reach binding international agreements because developing countries need affordable energy to grow their economies and reduce poverty, and individuals are reluctant to make lifestyle sacrifices [1 mark].

Related study guides