Topic 4

The Evolution of the AtmosphereTopic 4The AtmosphereLesson 1The AtmosphereMost of life on Earth today has evolved to survive in an oxygen rich environment. If these organisms of today were exposed to the Earths original atmosphere they would die very quickly.

Earths Original AtmosphereThe source of gases that formed Earths original atmosphere came from within the Earth. Molten rocks and material released gases trapped within the Earth. Volcanoes still do this today.

Earths Early AtmosphereThe relative proportion of gases are uncertain but scientists have determined the following gases to have made up the Earths early atmosphere:

Nitrogen N2Carbon Monoxide COCarbon Dioxide CO2Methane CH4Water vapour H2O

Earths Current AtmosphereScientists are able to perform first hand investigations to measure the gases of the atmosphere today. GasFormulaProportion (%)NitrogenN278.1OxygenO220.9ArgonAr.93Carbon DioxideCO2.035Others Ne, He, CH4.035Where did the original atmosphere go?Nitrogen: Most of this gas remains in the atmosphere because it is un-reactive.

Where did the original atmosphere go?Carbon Monoxide and Carbon Dioxide:The early atmosphere contained 100 to 1000 times as much carbon dioxide as it does today. These gases combined with calcium and magnesium dissolved in the oceans and formed carbonate sediments. This process is called precipitation. (Limewater Lab)

Where did the original atmosphere go?Hydrogen:Because hydrogen is so light, Earths gravitational field was not enough to hold this gas in the atmosphere. Most was lost into space.

Where did the original atmosphere go?Water Vapour:As the Earth cooled, water vapour in the atmosphere condensed and fell as rain.

Where did the original atmosphere go?Methane:Methane would have reacted with Oxygen which produces Carbon Dioxide and Water.

Where did the current atmosphere come from?Nitrogen:This gas remains from the original atmosphere.

Oxygen:Produced as waste during photosynthesis.

Where did the current atmosphere come from?Argon:Formed by the radioactive decay of elements within the mantle and is released as volcanic gas.

Where did the current atmosphere come from?Carbon Dioxide:CO2 is added to the atmosphere by volcanic eruptions, weathering of carbonate rocks, respiration of living things and in recent times by burning fossil fuels.

Where did the current atmosphere come from?Water Vapour:The water cycle continually recycles water vapour in the atmosphere.

Homework Write up Precipitation of Carbonate Minerals Activity 1.17 (pg 28) Prelim Spotlight Text in your lab books.

Precipitation of Carbonate Minerals PracLesson 2HomeworkComplete DOT Point 4.3 pg 22Early Life Forms-PhotosynthesisLesson 3StromatolitesThese are layered structures, believed to have been created from ancient bacteria.

StromatolitesThese ancient structures provide evidence for early life and have been found in Western Australia. They have been dated at 3.45 billion years old!!!

StromatolitesThese ancient organisms dominated the fossil record between 1 and 2 BYA. They are found in many different shapes and sizes but all have an alternating layers of lime and silt.

StromatolitesToday stromatolites are still forming and can be found at Shark Bay, Western Australia.

Formation of Present Day StromatolitesScientists have studies these present day stromatolites to learn what they may have been like 1-2 BYA. Scientists have discovered that they are formed by the actions of cyanobacteria.

Formation of Present Day StromatolitesCyanobacteria are prokaryotic (no nucleus) and are photosynthetic (use sunlight to make food and produce oxygen as a by-product).

Why does this matter?

BECAUSE THESE ORGANISMS PRODUCE OXYGEN!!! Something our early atmosphere did not have!!

Formation of Present Day StromatolitesThese simple bacteria photosynthesise and produce oxygen. See the equation for Photosynthesis below:

Is this process different from respiration?

Formation of Present Day StromatolitesYes it is, but how?Photosynthesis:

Respiration:Formation of Present Day StromatolitesIf ancient stromatolites were formed in the same way present day stromatolites are formed, what would be the implications regarding the free oxygen in the atmosphere?

Formation of Present Day StromatolitesThis has caused great debate.. And because there is no direct evidence about the ancient bacteria (they are not fossilised in the rocks) scientists are unable to conclude the exact processes they underwent.

HomeworkRead pages 30-31 Prelim Spotlight TextUpdate vocab listComplete DOT Point 4.1-4.2 pg 21