Earth’s Atmosphere

Noadswood Science, 2011

Earth’s Atmosphere• To know how the Earth’s atmosphere has changed over time

Tuesday, April 18, 2023

Atmosphere Word-search• Complete the Earth’s atmosphere

word-search…

Oxygen Percentage• How much oxygen is in the air?• Has it always been this amount – how can we tell?

• The percentage of oxygen in the air can be measured by passing a known volume of air over hot copper, and measuring the decrease in volume as the oxygen reacts with it

Copper + Oxygen Copper oxide

2Cu + O2 2CuO

Oxygen Percentage

• *There is some air in the tube with the copper turnings – the oxygen in this air will also react with the hot copper, causing a small error in the final volume recorded

• *It is also important to let the apparatus cool down at the end of the experiment, otherwise the final reading will be too high

Atmospheric Evolution• The Earth was formed about 4.5 billion years ago – its

early atmosphere was probably formed from the gases given out by volcanoes

• It is believed that there was intense volcanic activity for the first billion years of the Earth's existence – the early atmosphere was probably mostly carbon dioxide, with little or no oxygen

• There were smaller proportions of water vapour, ammonia and methane

Atmospheric Evolution• As the Earth cooled down, most of the water vapour

condensed and formed the oceans

• It is thought that the atmospheres of Mars and Venus today, which contain mostly carbon dioxide, are similar to the early atmosphere of the Earth

VenusMars

Earth’s Atmosphere Evolution• Earth’s atmosphere has changed drastically over the last 4

billions years…

Carbon dioxide

Methane Ammonia Nitrogen Oxygen Others

4 billion years ago Present day2 billion years ago

Atmosphere Changes• The proportion of oxygen went up because of

photosynthesis by plants

• The proportion of carbon dioxide went down because: -▫ It was locked up in sedimentary rocks, such as

limestone, and in fossil fuels▫ It was absorbed by plants for photosynthesis▫ It dissolved in the oceans

• The burning of fossil fuels is adding carbon dioxide to the atmosphere faster than it can be removed meaning the level of carbon dioxide in the atmosphere is increasing

Nitrogen• As oxygen levels rose atmospheric ammonia (NH3) reacted

with oxygen (O2) to form water (H2O) and nitrogen (N2)

• Also, living organisms, including denitrifying bacteria, broke down nitrogen compounds releasing more nitrogen into the atmosphere

• And so the atmosphere headed towards a composition that has remained fairly constant for the last 200 million years

Ozone• Oxygen normally exists as pairs of atoms (O2)

• Oxygen can, however, turn into another form that has three atoms joined together – this is ozone (O3)

• As oxygen levels rose, so did the amount of ozone

• This layer of ozone in the atmosphere filters out harmful ultraviolet rays from the sun – this will have allowed new organisms to evolve and survive

Atmospheric Changes

4 billion years ago Present day3 billion years ago 2 billion years ago 1 billion years ago

Volcanic activity releases CO2, methane, ammonia and water vapour into the

atmosphere

The water vapour condenses to form oceans

Green plants evolve which take in CO2 and give out oxygen

Carbon from CO2 becomes locked up in sedimentary rocks as carbonates and fossil fuels. Methane and ammonia react with the oxygen and nitrogen is released. Nitrogen is also

produced as a result of denitrifying bacteria on nitrates from decaying plants

Volcanic activity releases CO2, methane, ammonia and water vapour into the atmosphere. Some of the oxygen is

converted into ozone. The ozone layer blocks out harmful ultra-violet rays

which allows for the development of new life

Earth’s Atmosphere Evolution• The Earth's atmosphere has remained much the same for

the past 200 million years

• The main gas is nitrogen and oxygen (the gas that allows animals and plants to respire and fuels to burn) is the next most abundant gas

• These two gases are both elements and account for about 99% of the gases in the atmosphere – the remaining gases, such as carbon dioxide, water vapour and noble gases such as argon, are found in much smaller proportions

Carbon Cycle

Carbon Cycle• The levels of carbon dioxide in the atmosphere have not

changed must over the last 200 million years – this is due to the natural carbon cycle in which carbon moves between the oceans, rocks and atmosphere…