Chemistry - 13 The Earth's Atmosphere - 13.1 History of Our Atmosphere & 13.2 Our Evolving Atmosphere & 13.3 Greenhouse Gases

When is the Earth though to have formed?

4.6 billion years ago

Evidence of Earth's early atmosphere [2]:

- gas bubbles trapped in ancient rocks

- data gathered from other planets and moons

Theories for formation of Earth's atmosphere [2]:

- volcanic eruptions

- icy comets

What would the volcanic eruptions have released to form the atmosphere? [3]

- carbon dioxide CO₂

- water H₂O

- nitrogen N₂

Gases comprising early atmosphere [5]:

- (mainly) carbon dioxide CO₂

- water vapour H₂O

- nitrogen N₂

- (traces of) methane CH₄

- (traces of) ammonia NH₃

What gas was there very little of in Earth's early atmosphere, and why?

oxygen (O₂), as there was no life on Earth

Oxygen in Earth's atmosphere [4]:

- 3.4 billion years ago, simple organisms appear that can break down chemicals to release energy

- 2.7 billion years ago, organisms evolve into photosynthesising organisms such as algae

- plants evolve and colonise Earth's surface, converting more carbon dioxide to oxygen in the atmosphere

- previous organisms die out due to high oxygen concentration

Locked in carbon

carbon that is locked into a material, and therefore not in the atmosphere

What can carbon be locked into? [2]

- rocks

- fuels

Carbon locked into rocks [4]

- plants photosynthesise, converting carbon dioxide to glucose

- carbon from glucose becomes part of tissues

- animals eat plants and carbon becomes part of tissues

- tissues of plants and animals are covered by sediments and put under pressure, forming sedimentary carbonate rocks

Carbon locked into fuels [3]

- living organisms crushed by large-scale movements of Earth

- heated within Earth's crust over long periods

- making coal, natural gas and crude oil

Carbon sink

natural environment that absorbs and stores more carbon dioxide from the atmosphere than it releases

Volcanoes released [3]:

- methane CH₄

- ammonia NH₃

- nitrogen N₂

Methane and ammonia reacted with ...

oxygen from plants

Methane + oxygen →

carbon dioxide + water

Ammonia + oxygen →

nitrogen + water

Why was nitrogen not removed from the atmosphere?

it is very unreactive

Makeup of the atmosphere [5]

- nitrogen 78%

- oxygen 21%

- argon 0.9%

- carbon dioxide 0.04%

- trace amounts of other gases 0.06%

Greenhouse gas

gases that absorb energy radiated from the Earth's surface

The greenhouse effect [3]

- 30% of energy from the sun is reflected from the Earth

- shorter-wavelength radiation penetrates the greenhouse gases

- infrared (longer-wavelength) is absorbed by greenhouse gases, raising their temperature

What increases the proportion of carbon dioxide in the atmosphere? [3]

- burning fossil fuels

- rising temperature makes it less soluble in water

- deforestation reduces effectiveness of carbon sink

What increases the proportion of methane in the atmosphere? [3]

- swamps and rice fields

- emissions from grazing cattle and decomposing waste

- landfill sites

Evidence for greenhouse effect [2]

- trend of rising temperatures alongside rising carbon dioxide levels

- ice cores from sheets of ice