SIO40lecture6

SIO40lecture6 - SIO 40 Life and Climate on Earth Wed. Oct....

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SIO 40 – Life and Climate on Earth Wed. Oct. 6, 2010 Lecture 6 - How the planet changed with life, Part II Vegetation of the Carboniferous period
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Outline - Rise of ozone - Variations in atmospheric O 2 over the past 2 billion years - Evidence from the fossil record - Evidence from carbon isotopes - Regulation of atmospheric O 2 - Forest fires - Burial of organic carbon
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The rise of atmospheric ozone One important consequence of the increase in atmospheric O 2 concentrations was an increase in the concentration of ozone, O 3 , in the atmosphere. Ozone is formed via the following reactions: O 2 + h υ → O + O O + O 2 O 3
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The presence of ozone in the upper atmosphere is significant to the further development of life in the surface oceans and on land, because ozone serves as an effective shield for high-energy UV irradiation which would otherwise not be absorbed by other atmospheric constituents like CO 2 , O 2 , or H 2 O (right). This radiation, which is damaging to living things, is prevented from reaching the Earth's surface by ozone (below). Ozone absorbs harmful radiation
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When did the ozone UV shield develop? Models suggest that ozone increases nonlinearly with O 2 levels, so even a small amount of atmospheric O 2 can produce significant O 3 . Probably by the time O 2 had reached just 1% of its present level, the ozone screen was already reasonably effective. This would put the timing at about 1.9 billion years ago. Shielding effective by ~ 1.9 billion years ago
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Variations in atmospheric O 2 as indicated by fossil remains Ediacaran fauna (above), the first evidence of multi-cellular life, did not appear until 560 million years ago. These animals had flattened forms designed to maximize surface uptake of O 2 , perhaps indicative of low atmospheric O 2 at that time and previously. Only 20 million years later, the Cambrian fossils preserved in the Burgess Shale (right) demonstrated a much wider variety of body types, indicating that atmospheric O 2 levels must have been similar to modern times.
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The Relationship Between CO 2 and O 2 in the Earth system Photosynthesis produces organic carbon (CH
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This note was uploaded on 05/02/2011 for the course SIO 40 taught by Professor Barbeau,k during the Fall '08 term at UCSD.

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SIO40lecture6 - SIO 40 Life and Climate on Earth Wed. Oct....

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