 Panspermia is often criticized because it does not answer the question of the origin of life but merely places it on another celestial body.It was also criticized because it was thought it could not be tested experimentally.Wallis and Wickramasinghe argued in 2004 that the transport of individual bacteria or clumps of bacteria, is overwhelmingly more important than lithopanspermia in terms of numbers of microbes transferred, even accounting for the death rate of unprotected bacteria in transit.