Donald E. Johnson compiled a handy list of people who, beginning over a century ago, have suggested that extraterrestrials could have started life on Earth:
S. Arrhenius., Worlds in the Making, 1908.
Francis Crick, “The Origin of the Genetic Code” J. Mol Biol: 38, 1968, p. 367-379.
Fred Hoyle, The Intelligent Universe, 1983, pp. 16-17.
Bernstein. Max, Jason Dworkin, Scott Sandford, George Cooper, and Louis Allamandola, “Racemic amino acids from the ultraviolet photolysis of intestellar ice analogue,” Nature”: 416, 3/28/02
– from Probability’s Nature and the Nature of Probability, p. 32.
Even Richard Dawkins has stated that such intelligent design ay be possible (Ben Stein, Expelled: The Movie, 2008.), p. 32
And if so many great scientists entertain the idea, it must be substantial, so there.