Carbon Dioxide is very soluble in water.

So when oceans formed a lot of it would simply have dissolved in the water.

And dissolving CO2 forms carbonate ions which combine with some dissolved metals ions to form insoluble metal carbonates that precipitate into sedimentary rocks.

Once there were oceans and a reasonable temperature simple plants could evolve - probably something like the algae we have today.

Plants photosynthesise.

This reduces the amount of Carbon Dioxide even more.

And it produces Oxygen!

When there was enough Oxygen it was possible for animals to evolve.

Billions of tons of living things turned into fossil fuels over millions of years.

Living things are largely Carbon, so this (almost) permanently removed some of the Carbon from the atmosphere.

In Geography you have probably learned that the shells of sea-creatures are made up of Calcium Carbonate and that these can turn into Limestone and Chalk.

The Carbonate comes from dissolved CO2 in the ocean, so turning it into rock has locked up even more of the early CO2 for millions of years.

The balance of photosynthesis (plants only) and respiration (all living things) keeps the balance of Oxygen and CO2 fairly constant even today.

Although combustion (burning) and decaying matter are also involved in the balance.

The amount of Water Vapour in the atmosphere varies with temperature, season, location, time of day, biome etc.

But you should learn that when air is dried it is almost the same everywhere in the world.

It is

Around 20% Oxygen

Around 80% Nitrogen

With the rest being Noble Gases (mostly Argon) with a tiny amount (0.03%) CO2.

We don't really know for sure how much Methane or Ammonia there ever was in the atmosphere.

We just assume it would have been there because they are among the gases that come from some volcanoes today

In the graph above we see the theory that any Hydrogen and Helium  in the atmosphere would disappear quickly because these light gases can drift into space, and Hydrogen can react.

The theory also shows that when the water vapour condenses into oceans, the CO2 declines soon after.

We think that there would have been lots of Nitrogen right from the start because we have found this coming from volcanoes too.

We know that Ammonia is a very reactive gas, so we assume that it would have reacted with rocks and other substances quite quickly - which is why the % of Ammonia decreased quickly.

Methane also reacts quite easily so it also would not have existed in the atmosphere for long.

·         Atmosphere – the mixture of gases in the air

·         Noble Gases – Group 0 elements, unreactive

·         Billion – a thousand millions = 1,000,000,000

·         Volcanic Activity – Volcanic eruptions and release of gases from volcanoes

·         Condense – Gas turning to liquid

·         Sediments – solids that fall to sea floor eg mud, sand, Carbonates

·         Carbonates – substances that contain a metal bonded to Carbon and Oxygen only

·         Sedimentary Rocks – rocks formed at the bottom of the sea from sediments eg mudstone (from mud) sandstone (from sand, Limestone (from Carbonates)

·         Algae – simple plants

·         Photosynthesis – chemical reaction carried out by plants that uses water and CO2 to form sugars and Oxygen

·         Respiration – chemical reaction carried out by all living things to release energy

·         Acid Rain – rain with a pH less than 5.5

·         Respiratory problems – difficulties breathing (eg Asthma or Bronchitis)

·         Pollutant – substance in the environment that causes problems, usually released by people

·         Particulates – tiny solid particles in the atmosphere (usually  due to burning)