re: Carl Sagan plan for terraforming Mars
LJK asked:
"Could we genetically engineer plants that could survive and grow on Mars to do what Sagan initially planned?"
I doubt it. The Martian surface is too hostile. Also, as you said, Sagan's atmospheric model was bogus.
Many of the things that Sagan said were bogus. Sagan was a public relations genius but really a third rate scientist. The are many better authorities about Mars than Carl Sagan, e.g. the illustrious Nick Hoffman.
Gary
p.s. One thing that can certainly grow on the Martian surface are human settlements.