= The Life and Death of Planet Earth =
=== Peter D. Ward and Donald Brownlee  2002  0805067817 ===
=== booknotes ===

 . I learned a lot from Ward&Brownlee's '''Rare Earth''' (2000), and Ward's '''Under a Green Sky''' (2007)
  . I didn't see "Life and Death" until 10 years after publication, hence much of the contents are old news
 . Subject: Long term climate change in a world without geoengineering
 . Reiterates that we live at a time suited for intelligence, rare in Earth's very long history
 . More glaciations due
  . Root cause, weathering of Himalayas and abnormally low CO,,2,,
  . Previously warmer, wetter
 . Future heating due to sun heating
  . Solar heating because helium hotter at same pressure and density
  . Denser hotter core means faster fusion
  . Sun expansion at 7GY from now (not 10 as I remembered)  oopsie
 . Earth in old age - mostly because sun heating limits life span
 . Claims animal life possible only ± 500MY from now
 . Dismisses space technology
  . yes, rockets are expensive, book assumes forever
  . Moving to Mars 
   . Who needs another (too small) planet?
  . Moving earth with repeated cometary encounters
   . 100 km diameter comet, go to mars orbit, would lose moon
   . 2001 Don Korycanscky, Gregory Laughlin, Fred Adams
    . http://arxiv.org/abs/astro-ph/0102126   Feb 2001
    . 300 AU semimajor axis, 1e18 kg every 6000 years, 1 million times
    . my note:  how about ten 500 tonne objects a second?  Or 1 million 5 kg objects a second?
  . My heating recovery calculations:
   . Solar Shielding/reflector at 0.95 A.U., 10 grams per meter squared, 3e16 m^2^, 3e14kg
   . 12 km/s delta V, 20% efficiency, 100 year mass replacement rate, --> 36 Terawatts
   . 1e-13 of solar output