What is the lowest air temperature reliably measured on Earth's surface?

The answer

On July 21, 1983, Vostok Station recorded about −89 °C (−128 °F), the WMO-recognized record low for surface air temperature. Satellite sensors have hinted at even colder spots in high East Antarctic ice hollows, but Vostok still holds the classic thermometer record.

Correct answer: About −89 °C (−128 °F) at Vostok Station, Antarctica