Chemistry - 13 The Earth's Atmosphere

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

Effects of global warming [4]

- rising sea levels

- extreme weather

- changes in rainfall

- changes to distribution of wildlife

How does global warming cause rising sea levels? [2]

- melting ice sheets and caps

- thermal expansion

What will rising sea levels cause? [2]

- flooding of low-lying land

- coastal erosion

What could global warming change about rainfall? [4]

- temperature

- volume

- timing

- distribution

How could changes to rainfall affect us? [2]

- changing the food-producing capacity of some regions

- cause floods

Carbon footprint

total carbon dioxide emissions produced by an individual, group, or location

Carbon capture and storage

pumping carbon dioxide from fossil fuels underground to be absorbed by porous rocks

Problems with carbon capture and storage [2]

- has to be built and managed

- increases cost of electricity

Reducing methane production [2]

- reducing demand for meat (especially beef)

- using cattle-grazing fields for crops instead

How can governments reduce carbon footprint? [5]

- carbon taxes

- funding research on alternative energy

- support use of biofuels

- incentives to improve home insulation and conserve energy

- companies releasing greenhouse gases must offset emissions

Problems with reducing carbon footprint [3]

- debates about scientific evidence

- restrictions may hinder developing countries

- reductions have cost implications on manufacture and transport industries

Personal reductions of carbon footprint [3]

- use less electricity

- use personal vehicles less

- recycle waste where possible

Complete combustion of hydrocarbons

when sufficient oxygen is available, the products are carbon dioxide and water

Incomplete combustion of hydrocarbons

when insufficient oxygen is available, the products are carbon dioxide, water, carbon monoxide and soot

Why is carbon monoxide dangerous?

it is poisonous, as it reduces the ability of blood to carry oxygen

Why is soot dangerous? [2]

- accumulates in lungs

- causes global dimming

Where does sulfur dioxide come from?

oxidation of sulfur impurities in fossil fuels

Why is sulfur dioxide dangerous? []

- toxic to humans and animals

- causes acid rain

What are the effects of acid rain? [3]

- dissolves in lakes and rivers

- damages buildings (limestone, metal)

- alters pH of soil

Where do nitrogen oxides come from?

when nitrogen gas reacts with oxygen in the air

Why are nitrogen oxides dangerous? [3]

- toxic to humans and animals

- may trigger asthma

- cause acid rain