It will take about 3.3 million years for a normal day to be one minute longer than it is measured today, according to a study published Wednesday by UK researchers. Previous estimates had indicated it would only take 2.6 million years to add a minute to the day. The Earth’s decelerating rotation is why timekeepers globally adjust high-precision clocks every few years.
The Earth’s rotation is slowing for a host of reasons, according to researchers. There are astronomical effects, such as the braking effect of the mass of the moon. Also, the Earth is changing its shape due to smaller polar ice caps and changes in the average sea level since the last Ice Age. There are also electromagnetic forces operating beneath the Earth’s crust, which the study authors point out is contributing to a slower rotation.
And despite the team’s 3.3-million-year estimate, "geophysical forces operating on the Earth’s rotation will not necessarily be constant over such a long period of time," researcher Leslie Morrison said. Pending Ice Ages could also disrupt the team’s "simple" estimations, she added.
The team used calculations made by several ancient astronomers, including Babylonian, Chinese, Greek, Arab, as well as medieval Europeans and the translators who made their texts readable. Researchers found differences between solar eclipse predictions made by the early astronomers, and those discrepancies helped the team measure changes in the earth’s rotational velocity "since 720 BC," when early scientists began keeping records on eclipses, according to Morrison.