No. 78: Nov-Dec 1991
The concept of terraforming a planet is an old standby of science fiction; it is the process by which a technologically advanced race manipulates the surface and atmosphere of an uninhabitable planet so that it becomes inhabitable. We humans know to our dismay that we have the capacity to modify the earth's environment, but could we perhaps exercise better judgment and terraform Mars? C.P. McKay et al have looked into this possibility:
"From our analysis, one could propose the following sequence of events: production of CFCs (or other greenhouse gases) starts on Mars and the surface temperature warms up by about 20°K. The regolith and polar caps release their CO2 and the pressure rises to 100 mbar. One of two things could then happen. If there were large regolith and polar CO2 reservoirs, the pressure would continue to rise on its own. If these were absent, the CO2 pressure would stabilize, and additional CO2 would have to be released from carbonate minerals. At this point (perhaps between 100 and 105 years) Mars may be suitable for plants. If there was a mechanism for sequestering the reduced carbon, these plants could slowly transform the CO2 to produce an O2-rich atmosphere in perhaps 100,000 years. If sufficient N2 could also be released from putative soil deposits, and the CO2 level kept low enough, then a human- breathable atmosphere could be produced.
(McKay, Christopher P., et al; "Making Mars Habitable," Nature, 352:489, 1991.)
Comment. There is more to terraforming, but you get the idea from the above quote.
Now. J. Lovelock and others have speculated that our earth is much like a living orgaism that, with the help of the biosphere, maintains conditions suitable for life; that is, the Gaia concept. Terraformers of Mars would some-how have to induce Gaia to emigrate to Mars to regulate things there.
Or, since we are on a science-fiction kick, could it be that the earth itself was intentionally "terraformed" in the distant past and Gaia installed for our benefit -- or even someone else's benefit?