Scientists: Interstellar chemical clouds may have seeded the earth with building blocks of life, according to a new computerised model that suggests that biologically important molecules may have come from the space.The model, developed by Sandip Chakraborty at the S.N. Bose National Centre for Basic Sciences and his wife Sonali Chakraborty from M.M.C. College, both located at Calcutta, may explain why life evolved 600 million years after the formationof the planet 4.5 billion years ago.