4a

• Calcification


  Generation of seashells and similar forms: 2HCO3- + Ca2+ = CaCO3 + CO2 + H2O
• Carbon cycle


  Movement of matter from non-living to living compartments and back, transformation of matter from inorganic forms to organic and back
• Organisms in ecosystems


  • Energy "production" (really capture and conversion)
  • Elemental cycling (C and N particularly)
  • Transformation of energy and substances
• Earliest evidence of life comes from about 3.6 Gy ago
• Oxygen as a gas appeared around 2.7-2.5 Gy ago (evidence from rocks e.g. Fe3+)
• Life must have been anaerobic for c. 1 Gy
• Much of the oxygen in the atmosphere is derived from early photosynthesis
• May have caused an early mass extinction!
• Carbon sequestration


  1. Photosynthesis: CO2 + H2O --> O2 + C(H20)

  2. Calcification – generation of seashells and similar forms: 2HCO3- + Ca2+ = CaCO3 + CO2 + H2O
• Soil is the dominant terrestrial sink of atmospheric CO2
• Soil has lost between 40 and 90 Pg C because of human activity
• CO2 release


  • Fossil fuel burning accounts for about 80% of anthropogenic CO2 emissions
  • About 20% was accounted for by changes in land use, mainly large scale deforestation
  • About 45% of anthropogenic CO2 remains in the atmosphere
  • About 30% has been taken up by the oceans
  • The remainder has been taken up by vegetation, and soil
• Over geological time scales, marine plants have been taking carbon from the atmosphere (via the sea) and putting it into rocks (calcification) and fossil biomass (oil, gas and coal)
• By oxidising oil, gas and coal (burning fossil fuels) we are only partially redressing the balance
• Terrestrial fixed carbon is usually respired back to carbon dioxide
• Acidifying ocean


  Adding CO2 to the atmosphere reduces pH of the sea, predictions are in the order of 0.3 of a unit i.e. from 8.2 to 7.9 in the next 50 years
• Increasing acidity could reduce calcification
• Extant species evolved in a sea of pH 8.2 and the sea is more acidic than any time in last 500,000 years
• Animals may not be able to adapt, threatening species that rely on calcification reactions
• Calcification is the main means of sequestering carbon on the planet and has profound effects on climate
• Oceans are thought to have absorbed about half of the extra CO2 put into the atmosphere in the industrial age
• Extinction


  Extinction is a fundamental part of evolution, all species will go extinct eventually, but this normally occurs at a low rate, with only a few species going at a time
• Causes of previous mass extinctions

  • Bolide impact
  • Vulcanism
  • Increased oxygenation
  • Sea level changes
• Causes of previous mass extinctions have all been linked to major changes in climate over geologically short periods
• Effects of mass extinctions


  • Loss of species can lead to complete collapses of ecosystems
  • Plants as primary producers can lead to other extinctions if they are killed off
  • Some ecosystems are maintained by 'keystone species' and their loss leads to the extinction of many others
• It is suggested we are in the midst of a 6th mass extinction
• Species loss through human activities, combined with global climate change is causing ecosystem collapse and extinction rates many times the background levels
• Melomys rubicola reported extinct in 2016 the first directly attributed to climate change
• Is the next extinction set to be human mediated?
• Major pressures on ecosystems and species

  • Climate change
  • Deforestation and habitat fragmentation
  • Desertification
  • Pollution (air, water, sound and light)
• Huge swathes of the world have now lost at least 20% of their species and the ecosystems could collapse
• Many human cultures lived (more or less) sustainably within ecosystems. But technological innovations allowed the mass exploitation of species
• Unable to adapt to the rapid change in the situation, it is very easy for species to be rapidly depopulated
• The North American bison is a clear example, by the end of the 19th C there were only 300 wild buffalo
• Species at the top of the food chain are especially vulnerable – lower populations, slow breeders
• Demand for shark fin soup has decimated them, estimated to be a 70% loss of populations in 50 years
• Extinction of large mammals in North America

  • Woolly mammoths
  • American mastodons
  • Ground sloths
  • Giant armadillos
  • Camels
  • Giant deer
  • Giant bison
• Loss of large mammals in North America coincided with many changes including arrival of modern man and loss of habitat
• Temperature has powerful influences on individual metabolism – and, ultimately, entire ecosystems
• Ecological processes are temperature-dependent, e.g. beetle egg development rates increase rapidly with temperature