C1bL14 & 15 Air and its Evolution

Key Words

Air - a mixture of gases, mostly nitrogen and oxygen.

Argon - a Noble gas.

Big Bang - a titanic explosion from which the Universe was formed.

Composition - what something is made of.

Condense - change from a gas into a liquid.

Dissolve - a substance is dissipated into a solvent.

Gravity - an attractive force between objects that have mass.

Mixture - two or more substances in the same container but NOT chemically reacted.

Nitrogen - a gas that does not react readily.

Noble gas - a gas whose atoms have a full outer shell of electrons.  This makes them very unreactive.

Oxygen - A gas that readily reacts with other elements to form oxides.

Volcano - where magma erupts from the Earth to form a mountain consisting of ash and rocks.

Grade E

Air is a mixture of different gases as shown in the table below:

• The main gases in air are nitrogen and oxygen.
• Argon is more abundant than carbon dioxide.

The Earth's atmosphere was first thought to be hydrogen and helium, which were the most common gases after the Big bang.  These two gases are light and cannot be held by the Earth's gravity; they tend to escape into space.

Grade C

The gases in the table above can be shown as a pie chart:

The gases nitrogen, oxygen, and argon only can be seen.  The angles made by the others is far too small to see.

The composition of the air as we know it today has only been the same for about 200 million years and animals and plants have evolved to use these levels of gases.  Any change could affect life as we know it.

The Earth's earliest atmosphere came about due to volcanic activity.  The gases produced by volcanoes are mostly carbon dioxide and water.  As the Earth cooled, the water vapour condensed to form the oceans.  Carbon dioxide dissolved in the water, so its level in the atmosphere decreased.  Nitrogen was released from volcanoes as ammonia (NH₃).  The earliest atmosphere was poisonous.

The earliest life was in the seas.  Cells are, in effect, little bags of sea water..  The water protected this primitive micro-organisms from the powerful UV rays from the Sun.  These primitive organisms could convert carbon dioxide to sugars, releasing oxygen in the process.  Some oxygen was converted into ozone (O3) which stopped the UV rays getting thought.  This enabled plants and animals to colonise the land.

Eventually the levels of carbon dioxide, nitrogen, and oxygen balanced each other out.

Grade A

 Air bags are life-savers in cars.  They rapidly inflate when triggered by a sensor.  This generates a small current that sets off a chemical reaction in which sodium azide decomposes rapidly to form sodium metal and nitrogen gas.  This inflates the bags quickly.

Sodium azide  ® sodium metal + nitrogen

NaN₃ ® 2Na + 3N₂

The overcomes the problem of a gas bottle discharging., then not being able to blow up the bag when it's needed.

Carbon dioxide is a greenhouse gas, and Venus is hotter on its surface than Mercury, even though Mercury is closer to the Sun.  The heat from Venus is trapped, and this makes surface temperatures a hot as 600 ^oC.  As well as having a dense carbon dioxide atmosphere, it rains sulphuric acid, and the planet is rocked by incessant thunder. 

David Hardy

Venus is a dump.