Could humans survive underground?

Yes—humans can survive underground, and people have lived underground for long periods. The big difference is between shelter and a self-sustaining underground home.

To live there long-term, you need:

• Air control: ventilation, oxygen supply, and CO2 removal
• Water: aquifers or heavy recycling and filtration
• Food: artificial-light growing systems like hydroponics or aeroponics
• Power: a reliable source for lights, climate control, pumps, and farming
• Health support: no sunlight means vitamin D and circadian-rhythm issues; isolation can also hurt mental health

There are also risks from heat, radon, methane, and carbon monoxide deeper underground.

So the short answer is: yes, but only with serious engineering and life-support systems. Permanent, independent underground civilization is possible in theory, but very difficult in practice.