1.6 The Earth’s Changing
Atmosphere
Unit 1 Theme 1
My Wider World
Learning Objectives
• How did the Earth’s early atmosphere
probably form?
• What gases could have been present in the
early atmosphere?
• How did the proportion of oxygen in the air
gradually build up?
The Earth’s Atmosphere
• Atmosphere first formed billions of years ago
• Very different to how the atmosphere is now
The atmosphere now
• http://scijinks.nasa.gov/atmosphereformation
Young Earth’s first proper atmosphere
• First atmosphere
was probably
produced by the
volcanoes that
covered it’s
surface
• Volcanoes release
mainly carbon
dioxide and water.
The Earth’s early atmosphere
Gas formula
•
•
•
•
•
•
Oxygen
Carbon Dioxide
Water Vapour
Methanol
Ammonia
Hydrogen
O2
CO2
H2O
CH4
NH3
H2
Photosynthesis
• Water vapour in the atmosphere cooled and
condensed
• Oceans started to form
Single celled organisms
• Algae – living in the oceans
• Used carbon dioxide in photosynthesis
• Carbon dioxide and water form glucose
(sugar) for the organism to use as energy
• Oxygen gas is given off
• Population of organism grew
• So they absorbed more and more of the
carbon dioxide in the atmosphere
Atmosphere with microorganisms
Microorganisms produce oxygen
• Oxygen built up slowly
• Reacted with methane, making carbon dioxide
and water
• Oxygen reacted with ammonia, producing
nitrogen and more water
• Oxygen + methane = carbon dioxide and water
• Oxygen + ammonia = nitrogen and water
More microorganisms
photosynthesis
• reduced amount of carbon dioxide in the
atmosphere
• Increased the amount of oxygen
• Nitrogen increased as oxygen reacted with
ammonia
• Nitrogen is unreactive – so it just stayed in the
atmosphere
Word equation for photosynthesis
• Carbon dioxide + water = glucose + oxygen
• http://www.bbc.co.uk/learningzone/clips/pho
tosynthesis/13515.html
• http://www.bbc.co.uk/learningzone/clips/pho
tosynthesis-in-plants/212.html
Billions of years ago
NO HUMANS!
•
•
•
•
How atmosphere developed is theory
Good evidence researched by geochemists
Gives clues about how life began
1950’s Miller and Urey simulated earth’s early
atmosphere
• They fired electricity through a mixture of
ammonia, methane, hydrogen and water
• Produced amino acids – proteins essential to life
Did you know?
• It is unlikely all the water on Earth came from
volcanoes
• Maybe it arrived in comets that collided with
the Earth billions of years ago
Key points
• The Earth’s early atmosphere was produced by
volcanoes, and was mainly carbon dioxide, water
vapour, methane, hydrogen and ammonia
• As the water vapour cooled, the first oceans
formed and early plants began to evolve
• Early microorganisms used carbon dioxide in the
atmosphere for photosynthesis. This made
oxygen gas, which in turn converted ammonia
into nitrogen
• http://www.bbc.co.uk/schools/gcsebitesize/sc
ience/aqa/earth/earthsatmosphererev3.shtml
• http://www.bbc.co.uk/schools/gcsebitesize/sc
ience/aqa/earth/earthsatmosphere/quiz/q403
50564/
• http://www.bbc.co.uk/learningzone/clips/pho
tosynthesis/13515.html
• http://www.bbc.co.uk/learningzone/clips/atm
ospheric-evolution-on-venus-earth-andmars/9823.html