Cenozoic

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  • Created by: sikemi__
  • Created on: 13-05-21 16:06
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  • Climate change during the Cenozoic
    • What is the Cenozoic?
      • Means 'new life'
      • Resetting of the biological clock following mass extinction at the end of the Cretaceous and the beginning of the Palaeocene
      • We are still in it - began around 66 million years ago
    • Role of foraminifera
      • Forams - single celled organisms that secrete calcium carbonate shells
        • Found in abundance in upper ocean and in sediment at depth
      • Oxygen isotope ratios of shells depend on temperature and oxygen isotope ratio of sea water at time of calcification
        • Signal can survive for 100s of millions of years as fossils
          • Can be used to find estimates of past ocean temperature (evaporation from ocean surface favours oxygen 16)
      • What they showed...
        • Global mean temperatures are around 14.5 degrees C now but were around 25 degrees C at the start
        • Temps peaked around 50 million years ago but Earth cooled steadily until around 34 million years ago
        • Temperature was more or less stable until around 15 million years ago when cooling resumed
          • Pace accelerated around 5 million years ago
        • Overall cooling trend of over 10 degrees C
    • Geological carbon cycle
      • CO2 abundance in the atmosphere can control Earth's climate via greenhouse effect
        • Changes in fluxes of sources and sinks are critical
      • Primary source of CO2 on geological timescales = volcanic gassing
        • Controlled by global rates of sea floor spreading and subduction
      • Key sink = chemical weathering of silicate rocks
      • An imbalance between sinks and sources leads to feedbacks
      • One hypothesis for Cenozoic cooling is that global sea floor spreading rates fell over the past 60 million years
        • This would decreasing the CO2 flux from the Earth's interior, depleting the atmosphereof it
          • However, sea floor spreading rates increased, so this doesn't explain
    • Reasons behind cooling
      • Several mountain ranges were establishedduring this time e.g. Rocky's, Himalayas, Alps
        • This led to increased global weathering rates due to exposure of fresh rock and glaciation
          • This then led to CO2 drawdown from the atmosphere, so cooler climates (as CO2 is a GHG that absorbs energy and re-emits, some back to Earth

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