Your ignorance is showing.
Why are you so aggressive and condescending when it comes to discussing race issues? What authority do you think you have to be the final say on race? Seriously, calm down.
Slavery was not racially justified before colonialism in the modern sense, true, but that doesn't mean discrimination didn't exist based on what is basically the equivalent of racism.
The human brain differentiates what we see, and I find it implausible that in history (whether it be 3000 BC, 500 AD, or 1200 AD) humans have not discriminated against each other, based on what you consider "modern racism".
When Europeans first made contact with Native Americans, the Natives
did freak out. It wasn't always a "racist" reaction, but that proves that people differentiate based on skin color, as Native recollections often mentioned pale skin and lighter features. So yes, it is certain that racism did exist in some form or another among people before modern racial science came about.
White people did not "invent" racism. I get you've jumped on the "check your white privilege" bandwagon from your post history, but arguing there was nothing remotely like racism before evil white people just invented it is ridiculous.
Okay, cool. Then get off the topic if it bores you so much. Create your own thread about race, don't derail this one on gay marriage.