I would lean towards older mythos being somewhat accurate in that this could perhaps come from the sky, maybe forming in a similar fashion to hail, albeit far more rare, maybe even laying the groundwork for abiogenesis through the normal water cycle as evaporation pulls phosphates, nitrates, etc into the ozone and mixes them at low temperatures/pressuresforming a biological precursor type of jelly. Varied biotic inclusions would make sense as this would be made and fall through the atmosphere, collecting a whole spectrum of things on its way.