Single-walled carbon nanotubes (SWNTs) were grown from the condensed phase by thermally post-annealing of a soot-like material, possibly containing precursors for SWNT growth. The soot-like material was obtained by laser ablation of Ni-Co-graphite composite targets at 550-700 degreesC. This initial material did not contain any SWNTs but postannealing treatment inside an electric furnace at 1200 degreesC under argon flow resulted in SWNTs. The soot-like material prepared at lower temperatures (room temperature to 400 degreesC did not yield SWNTs even after post-annealing. These results indicate that the precursors for the growth of SWNTs can form only above a certain threshold temperature, about 550 degreesC. Once these precursors are present, SWNTs can grow by annealing of the metal-carbon mixture. A growth model is proposed based on these results.