Complex molecules introduced to Earth only by comets ? ? ?
Good Lord...does being a comet naval gazer prohibit any study of Earth geology ? ? ?
Earth's fission of 2 million cubic miles of Uranium and Thorium produces enormous heat, pressure and 'elemental' atoms in an elemental refinery producing a wide range of complex compounds, including many organic ones, like Hydrocarbons, see
"Fracturing the Fossil Fuel Fable" under Geonuclear at the FauxScienceSlayer site.