|Postcard from Panspermia|
There have long been discussions about how life began. Experiments have suggested that life on Earth could have begun right here, through interactions between lightning and the early atmosphere.
Panspermia supplies an alternate option. It's based on the assumption that some kinds of life can survive in space for an indefinite period. Humanity has already found that some bacteria are able to do this from a satellite called LDEF, sent into space in 1984 and recovered in 1990. Various experiments showed that the spores survived for 6 years, particularly those embedded in clay or environments replicating the inside of a meteorite.
Panspermia carries this further, suggesting that primitive life has long term survival capability inside meteorites, and it is able to seed planets with life from the impacts. It allows evolution to be "jump started" by providing a distribution mechanism.
It's based on a mixture of observation and experimentation. We have observed that bacteria can survive in space both in simulated natural environments (the artificial meteorites mentioned above), and with direct exposure to outer space on the skin of ISS and LDEF. Experimentation in the form of simulations suggests that the debris thrown away from a planet like Earth following a large meteor impact can include bacteria. Putting the two together, any planet where life evolves and experiences large impacts can then seed other planets from smaller meteorites as they impact.
It doesn't really solve the quesiton of the origin of life, just provides an opportunity to move it elsewhere.