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Will Earth no longer define time? Leap second could be abolished.

The rotation of the Earth has defined time for as long as time has been kept, but keeping up with all of Earth's little quirks by adding and subtracting an occasional leap second is getting tiring. Timekeepers could vote Thursday to rely solely on atomic clocks. 

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The headquarters of the International Telecommunication Union in Geneva, seen Monday. ITU's member states are meeting in Switzerland this week to consider abolishing the leap second. The U.N. telecoms agency says countries are poised to decide this week whether to drop the 40-year practice of adding leap seconds to keep atomic clocks in sync with the Earth day

Frank Jordans/AP

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After millenniums as humanity's timekeeper, Earth may be about to get a pink slip.

Delegates to the International Telecommunication Union's Radiocommunication Assembly are slated to vote as early as Thursday on a proposal to scrap the leap second – an occasional tweak to atomic clocks designed to sync them with time defined by Earth's rotation.

A "yes" vote, which many expect, would leave atomic clocks as the sole international standard for determining the length of a second, and by extension, a day. For the first time in human history, the length of a day would be uncoupled from Earth's day-night cycle.

The leap second has been used since 1972 to adjust for a long-term slowdown in Earth's rotation. The slowdown is inevitable, but the pace is irregular.

Advocates for the change argue that leap seconds require fiddling with atomic clocks at these irregular intervals, raising the prospect that human error could crash large-scale computer networks, cell-phone systems, and other vital pieces of today's high-tech infrastructure. They rely on highly precise timing to operate.

Critics counter that the leap-second system has worked well since 1972, when the parallel timekeeping process was adopted internationally. Moreover, they say, killing off the leap second merely kicks the need to adjust the clocks down the road, when the gap between the two approaches would be even wider.

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