Which global time standard replaced Greenwich Mean Time as the basis for civil time in 1972?

Coordinated Universal Time replaced Greenwich Mean Time as the international basis for civil time in 1972.

UTC combines atomic-clock precision with a close connection to Earth’s rotation. It is based on International Atomic Time, produced from atomic clocks around the world, while leap seconds have historically been added to keep UTC within about 0.9 seconds of UT1, a measure based on Earth’s rotation.

GMT had long served as the world’s reference time, but Earth does not rotate at a perfectly constant rate. Atomic timekeeping therefore provided a more stable foundation. The modern UTC system, including one-second leap adjustments, was implemented on 1 January 1972.

GMT remains widely used as a synonym for UTC+00:00, especially in everyday British usage, but the terms are not technically identical. Universal Time is also a related family of astronomical time scales, not the full name of the global civil standard.