relict

In this context the "relict glacier" and the possible buried sheet of glacier ice around it, might be remnants of the latest glaciation episode affecting the Noctis volcano.

Perseverance is the tip of the spear in humanity’s grand quest to find traces of a relict Martian biosphere.

Either the tiny relict population had winked out, or the original sightings had been in error.

"Its living flora, with the highest concentration of primitive, archaic and relict taxa known, is the closest modern-day counterpart for Gondwanan forests," says the UN body.

An “abundance of unique, isolated communities … have provided refugia for many ancient plant species” and sheltered “… an extraordinary number of areas of relict vegetation … where natural processes continue unaltered.”