How long was prehistory vs. history? (i also don't understand the sentence as well)

150k-170k years of prehistory and around 30k years of history; The question is essentially asking how long humans have existed vs. how long humans have recorded data about their existence.

interdependence is when all participating groups and individuals depend on each other. if you depend on one anothers goods, you end up trading in order to get the items you're looking for. (for ex: if i have food and you have water, we trade in order to depend on each other to live)