Velikovsky perceived his Exodus comet as raining hydrocarbons on the Earth – among other things less salubrious. We now know meteorites contain hydrocarbons – and so do comets. Planet sized comets are not necessary – just your run of the mill comet such as Comet Churiyumov Gerasimenko (visited by the Rosetta Mission). At https://phys.org/print435919207.html … we learn that instruments aboard the space probe Rosetta analysed dust particles ejected from the comet's nucleus. This research was published by the Royal Astronomical Society in December of 2017. The study found that, on average, half the mass of each dust grain consisted of carbonaceous material with a mainly macromolecular organic structure. The other half was mostly composed of non-hydrated silicate minerals. One instrument, ROSINA, analysed the gases emitted – which includes water vapour from frozen ices. To be exact, water vapour, carbon dioxide, carbon monoxide, molecular oxygen, and various other small organic molecules derived from carbon, hydrogen, nitrogen and oxygen atoms.
Other instruments such as onboard cameras and an imaging spectrometer studied the surface of the comet. They found it is very black – just like mythology indicates. This, they think, is due to a high organic carbon content. The dust particles, however, are also useful to understand the make-up of the comet – representative of its non volatile composition. They reflect the make-up of the nucleus. The analysis records that comets are largely carbon and silicate and sublimation of gases is different to the dust grains – which do notr show up any evidence of change by liquid water. They may not have been modified since the beginning of the solar system. In other words, if comets brought life to earth via carbon rich material being dumped into the atmosphere it could have been via the macromolecular compounds.