A weird idea I'll admit but I think it would be cool if humanity developed a sort of interstellar seed and made earth into some sort of giant dandelion ball shedding seeds on the cosmic winds.

But what would these seeds look like? What type of life would they contain? What design features would be necessary for the successful fertilisation of other primed but lifeless earthlike planets? What sort of propulsion system should it operate or would it need one? What hurdles would the seed face on its perilous journey to begin evolution on other worlds?

My suggestions; i would use extremophiles- specifically a methanogen (which consumes Co2 and forms methane) because extremophiles can survive incredibly extreme conditions, are relatively radiation resistant and form dormant spores that can stay viable for 100s of thousands of years.

The bubble seed would be filled with dry ice, regular ice and extremophiles. When it enters a solar system and the amount of solar radiation increases, the heat is captured in the capsule and sublimes the ice into gas and reg ice into water. The extremophiles activate and metabolize the co2 into methane which is then siphoned and ignited to cause thrust in a methane engine.

The methane engine would be used to navigate in solar systems and also to power a slower descent through a suitably dense planetary atmosphere. It could also be used to power rotation of the seed forming a dynamo which generates a magnetic field around the capsule reducing the effects of solar radiation on the content. The seed may also be helicopter shaped so as to have a controlled decent in a spin through air.

When the spinning seed hits a hard surface it will open and the centrifugal force will be used to throw the extremophile colonies outwards from the seed onto the planets surface to maximise the likelihood that they will land somewhere suitable.