Some scientists believe that active plate tectonics are important, even essential for renewal of a planet's biosphere.
Currently it appears Mars does not have active plate tectonics, though it may have had a similar system to Earth's at one time.
Most think that the dry cold and arid state we see today was caused by radiation. If Mars has a magnetosphere it's probably weak. At one time it may
have had a molten core, say for the first billion years, but it's now probably solid, due to cooling of this smaller planet.
Now most scientists tend to believe that the samples they've seen are not biologically active, but they're not so sure they'd not put them in
quarantine were they to bring any samples back to Earth.
The question is, then, could we revive Mars, warm it up, regenerate an atmosphere which would reduce radiation and support some kind of biological
life, bacteria, leading to the growth of primitive plants.
Some relevant links:
Chris McKay Lecture (1999):
MARS: MAGNETIC FIELD AND MAGNETOSPHERE by Luhmann&Russell:
It would take time, 100 years minimum but with more advanced methods it might take less.
Are we certain the liquid ocean is H2O? Many people think so based on magnetic field measurements. There are various theories as to why it's warm
enough to remain liquid under the relatively thick crust, but we're still not sure, AFAIK, that it's a shallow ocean or a deep one.
ISTM, that if there's a liquid ocean it may be other than H2O, and could be something like a liquid hydrocarbon.