Revolutions That Made the Earth

Tim Linton and Andrew Watson, Oxford University Press, Multco 550 L574r 2011

Like Melanie Lenart's Life In the Hothouse, this book posits a biosphere shaped by life.

Like Rare Earth, this book suggests life

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Endpapers: 8 stages of evolution

• 1 Compartments
• 2 Chromosomes
• 3 Genetic code - critical step
• - Oxygenic photosynthesis - critical step
• 4 Eukaryotes - critical step
• 5 Sex
• 6 Cell differentiation in eukaryotes
• 7 Eusocial colonies
• 8 Natural language - critical step

Ch 8 - Photosynthesis

• p145 We are obligate oxygen breathers - aerobic metabolism produces 14 times as much combustion energy as anerobic (2870 kJ/mol vs 195 kJ/mol for fermenting lactic acid).
• p150 Photosystem II and photosystem I, PS2 and PS1 are a multistage process to produce oxygen by splitting water
  • WSC - Water Splitting Complex, 3 Mg and a Ca surounded by proteins, 4 photons
• p152 LHC - Light Harvesting Complex, pigment molecules that gather and focus light on chlorophyll molecules in a nearby reaction center.
  • One pigment molecule absorbs a photon rarely, a few Hz, to feed picosecond-scale reactions
• p154 about 100 carefully ordered proteins, a huge number of genes, difficult and slow to arrange by evolution
• p155 fusion of two anaerobics

Ch 9 - The trial of the oxygen poisoners

• p166 Fig 9.1 timeline - anerobic photosynthesis at 3.7 Gya, certainly before 3.4 Gya, oxidized paleosols after 2.2 Gya
  • anaerobes can produce stomatolite mats and other carbon deposits, resemblance to cyanobacteria fossils does not prove oxygenic photosynthesis

My take - the earth formed 4.56 Gya, complex anerobic organisms formed over 0.8 Gy, oxygen photosynthesis needed 1.5 Gy to develop - once. Humans evolved only 0.1 Gy before it will become too hot to do so. Perhaps a G3 or colder star might last longer than our G2, and a planet at Venus's position would offer a wider window for the production of us.

Ch 21 - Where Next?

• p396 Box 21.2 In the case of methane release from the Arctic tundra the best scientific estimates of the strength of the feedback are that it is two orders of magnitude weaker than the runaway condition.
  • no refs,
• p397 4e15 kg of total carbon fuels → 1000 ppm CO₂, 6℃ global warming.
• p406 Current energy inputs to agriculture are only around 3% of total human primary energy production

  • no refs, but see http://www.fao.org/docrep/003/x8054e/x8054e04.htm fig. 1.7