Here's a more comprehensive Science News article from yesterday about the current panspermia debate:

http://www.cosmiverse.com/science01110204.html

And an excerpt which informs about the original theory:

The idea was first proposed in 1903 by the Swedish chemist Svante Arrhenius, who suggested that solar radiation could propel single spores across solar systems. In the 1970s, astronomers Fred Hoyle and Chandra Wickramasinghe studied the infrared spectra of interstellar grains of dust, concluding that they were dried, frozen bacteria.

They put forward the controversial suggestion that life on Earth started when such bacteria arrived from space. But critics said cosmic rays and ultraviolet radiation from the Sun would kill unprotected spores.