Black holes are regions in space where gravity is very strong—so strong that nothing that enters them can escape, including light. Theoretical predictions suggest that there is a radius surrounding black holes known as the event horizon. Once something passes the event horizon, it can no longer escape a black hole, as gravity becomes stronger as it approaches its center.

A 210,000-year-old skull has been identified as the earliest modern human remains found outside Africa, putting the clock back on mankind's arrival in Europe by more than 150,000 years, researchers said Wednesday.