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Module 4 Lesson 1. Formation of the Earth and the early atmosphere
Terms in this set (19)
Banded Iron Formations (BIFs)
The layers of iron oxide (Fe2O3) suggest periods of alternating oxygen-rich and anoxic conditions. Huge deposits of BIFs date to the Great Oxygenation Event.
The process by which organisms use light energy to convert water and carbon dioxide into oxygen and high-energy carbohydrates such as sugars and starches. The origin of the O2 in the atmosphere
Oxygen crisis (Great Oxygenation Event)
As concentration of oxygen in earth's oceans increased, it began to react with iron
This reaction continued to consume oxygen for about 1.8 billion years until most of the iron ions had reacted fully
Layered rock that results from the activities of photosynthesising prokaryotes called cyanobacteria. The bacteria bind thin films of sediment together.
The 1st Eon. The atmosphere was composed of hydrogen, methane, ammonia and lots of CO2. The surface of the Earth was liquid rock. It was too hot for liquid water.
Lots of CO2 and methane in the atmosphere. The first oceans formed by condensation of water vapour. By 4 Billion years ago the late bombardment had ended and the lithosphere was being moved by plate tectonics.
By 2.3 billion years ago sufficient O2 had been produced by photosynthesis that all the reduced iron had been oxidised and free O2 entered the oceans and the atmosphere.
The mass extinction of anaerobic organisms.
The ecosystems of anaerobic microorganisms were likely devastated by the appearance of toxic free oxygen. Aerobes evolved which could immobilise the free oxygen using enzymes.
The protective layer in atmosphere that shields earth from UV radiation probably didn't form until O2 levels in the atmosphere reached near the current levels probably in Ordovician times
Obligate anaerobic bacteria
For the 1st billion or so years of life the organisms were anaerobic. Today their decedents fill niches in anaerobic habitats in sediments and rocks.
Some bacteria are obligate aerobes and use O2 in respiration as we do. Other bacteria are facultative aerobes and can tolerate O2.
A model ecosystem containing regions of aerobic and anaerobic sediment for microbes of diverse metabolism.
Carbon dioxide dissolved in water chemically reacts with the water to make carbonic acid. Carbonic acid reacts with minerals in rocks to produce soluble carbonate and hydrogen carbonate ions. The soluble ions travel to the oceans where they may be precipitated out to form limestones. Carbonation weathering and photosynthesis removed CO2 from the atmosphere during the Archean Eon.
Evolution of the Atmosphere
CO2 levels have decreased because weathering and photosynthesis have transferred the C to the lithosphere.
Oxygen levels have increased because of photosynthesis.
Ozone levels have risen.
A unicellular organism that lacks a nucleus and membrane bound organelles. All life was prokaryotic until eukaryotes evolved about 2 billion years ago. Even today prokaryotes outnumber, outweigh and outcool eukaryotes.
Larger, complex cells with nucleus and membrane bound organelles. By 1.5 Billion years ago the 3 major eukaryotic groups, the animals, plants and fungi, had probably diverged from their common ancestor.
Microbial mats were the major ecosystems of the Archean. A microbial mat is a mm's to cm's thick layer of phototrophic (light food) and/ or chemolithotrophic (chemicals in rocks food) bacteria living on Archean ocean floors. For 3.5 billion years this was the dominant ecosystem on the planet.
formation of the oceans
As the planet cooled after the late bombardments the atmosphere and surface cooled enough to make the water vapour condense to form oceans
Carbon dioxide peak
Peak CO2 from vocanic eruptions. Co2 drops as weathering and photosynthesis remove CO2 from atmosphere
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