SCD Type 2 Implementation Challenges: but Sources data are without Business Key/ Primary key any one help

I want to implement SCD Type 2 but there is no business key or primary key is available from the source. The table contains 200+ columns and billions of rows. Has any one faced this issue in prod and what are the best solution for that.if we are going to create hash keys then how can we deal witb nulls ,blank, bad data.