As I understand it, the strict definition of Jewish descent is purely. You have to go back around 100-200k years to reach the most recent common matrilineal ancestor, and I'm reasonably confident she was not Jewish.
How many ancestors you have it just a function of how many generations you look back, and with each successive generations it doubles. At some point in the past, the entire world is your ancestor.
https://www.nbcnews.com/sciencemain/all-europeans-are-relate...