U ovom slučaju je množina u rečenici pa onda grounds. Eiječ ima mnogo značenja, ovo je jedno od njih.npr. "You don't have a ground to support that"Dakle utemeljenje ili uporište, nešto n čemu se temeljno zasniva neki koncept (u ovom slučaju je to život)

Croatian term (edited): najdublja uporišta nacionalnog identiteta

najdublja uporišta nacionalnog identiteta

najdublja = it makes more sense to see it as "roots of ..." or "foundations of ..." or "fundamental traits of ..." or similar.

Nemam potvrdu za kontekst

Human Dignity in Bioethics: From Worldviews to the Public Square

It is in that context that the demands for cooperation and altruism, for social equity, and fairness in exchange gained their deepest foothold in our psychological phylogeny. Eventually, around 15,000 years ago, we settled down and began to practice agriculture and to build cities. At that point, we made a relatively successful ..

Celebration Capitalism and the Olympic Games
https://books.google.rs/books?isbn=1135938261
Jules Boykoff - 2013 - ‎Sports & Recreation
The 2004 Athens Olympics Greece is the birthplace of the ancient Olympics, and the Games have long held a firm foothold in Greek national identity.

https://www.indifferentlanguages.com/words/foothold/croatian