abiogenesis and spontaneous generation are one in the same thing in terms of biology.
they describe a process (as opposed to a singular pinpoint "event").. that process being that the first life on earth resulted from inanimate components
th eproblem comeinto the play once u go a bit deeper. ppl tend to equate the words "spontaneous generation" with some sort of mystical magic trick where u have nothing and and then all of a sudden u have a fully formed creature.. thats not how it works and not the process defined by abiogenesis.
what i mean by reducing atmosphere is that the early earth atmosphere was rich in hydrogen. a reducing atmosphere (and in earths case lets be clear.. it was "mildly reducing, but reducing nontheless) contains molecules that are able to "reduce" other molecules... most importantly to this topic is that a mildly reducing atmosphere allows "organic" molecules to form (made up of carbon, hydrogen, and oxygen and sometimes nitrogen)
the early earth atmosphere (due to its constant bombardment with meteorites and volcanic activity) provided all the necessary components.
the issue now is,, whether the components that led to life on earth are really terrestrial (originating from earth) in origin or did the earth get "seeded" with these components via hitching a ride on a meteor from another planet.