Panspermia (from Greek πᾶν (pan), meaning ""all"", and σπέρμα (sperma), meaning ""seed"") is the hypothesis that life exists throughout the Universe, distributed by meteoroids, asteroids, comets, planetoids and, also, by spacecraft in the form of unintended contamination by microorganisms.Panspermia is a hypothesis proposing that microscopic life forms that can survive the effects of space, such as extremophiles, become trapped in debris that is ejected into space after collisions between planets and small Solar System bodies that harbor life. Some organisms may travel dormant for an extended amount of time before colliding randomly with other planets or intermingling with protoplanetary disks. If met with ideal conditions on a new planet's surfaces, the organisms become active and the process of evolution begins. Panspermia is not meant to address how life began, just the method that may cause its distribution in the Universe.Pseudo-panspermia (sometimes called ""soft panspermia"" or ""molecular panspermia"") argues that the pre-biotic organic building blocks of life originated in space and were incorporated in the solar nebula from which the planets condensed and were further —and continuously— distributed to planetary surfaces where life then emerged (abiogenesis). From the early 1970s it was becoming evident that interstellar dust consisted of a large component of organic molecules. Interstellar molecules are formed by chemical reactions within very sparse interstellar or circumstellar clouds of dust and gas. The dust plays a critical role of shielding the molecules from the ionizing effect of ultraviolet radiation emitted by stars.Several simulations in laboratories and in low Earth orbit suggest that ejection, entry and impact is survivable for some simple organisms.