Notes and References

1. In this calculation it has been assumed that water ice accounts for two-thirds of the volume and that there are 5 x 1012 cometary nuclei in the Oort Cloud.

2. To achieve planetary status an object must satisfy three conditions. First, it must orbit the Sun; second, it should be spherical due to its own self-gravity; and third, it should have cleared the immediate neighborhood of its orbit of smaller objects. If an object only satisfies the first two conditions, then it is designated a dwarf planet. All other objects are collectively considered to be small Solar System bodies.

3. It should be noted, however, that there are many factors involved in sea-level rise and island-land loss, not all of which are directly related to global warming.

4. The history of the Tikopia is discussed in detail by Jared Diamond in his book Collapse: How Societies Choose to Fail or Succeed [Penguin Books, New York (2005)]. Photographs of the island of Tikopia and its people can be found at http://home.netcom.com/~yellowrose/tikopia/index.html and http://janesoceania.com/solomons_tikopia/index.htm. Many further web links can be found at http://en.wikipedia.org/wiki/Tikopia.

5. The critical component deciding the Earth's fate is how much mass the Sun loses during its red giant phase. A recent set of solar model calculations published by Klaus-Peter Schroder (Universidad de Guanajuato, Mexico) and Robert Smith (University of Sussex, UK) in January of 2008 [Distant future of the Sun and Earth revisited, available at http://arXi-v.org/abs/0801.4031] suggests that the Earth will be consumed during the Sun's asymptotic giant branch phase, when it undergoes thermal pulsations just prior to forming a planetary nebula. These authors also note that while the mass loss from the Sun will result in the Earth acquiring a larger orbit, tidal interactions between the Earth and the Sun's extended outer envelope will tend to make its orbital radius smaller. Exactly which mechanism will dominate is partly dependent upon what assumptions go into the calculations, and accordingly there is still a good deal of uncertainty as to whether the Earth will survive or not. Schröder and Smith do note, however, that the greater the Sun's mass loss rate the more likely it is that the Earth will survive. Large-scale mining to reduce the Sun's mass is therefore one possible operation that our distant descendants might wisely initiate. Such a process also ties in well with the rejuvenating scenario described by Beech [see Chapter 2, Note 3].

6. A transcript of Levin's talk can be found at http://arxiv.org/abs/ 0705.3176.

7. Carocco's detailed re-analysis of the Viking Lander data can be downloaded at http://electroneubio.secyt.gov.ar/First_biological_classification_ Martian_organism.pdf.

8. The abstract to Houtkooper and Schulze-Makuch's paper is available at http://www.cosis.net/abstracts/EPSC2007/00439/EPSC2007-J-00439.pdf.

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