<P> The current rate of tidal deceleration is anomalously high, implying the Earth's rotational velocity must have decreased more slowly in the past . Empirical data tentatively shows a sharp increase in rotational deceleration about 600Myr ago . Some models suggest that the Earth maintained a constant day length of 21 hours throughout much of the Precambrian . This day length corresponds to the semidiurnal resonant period of the thermally - driven atmospheric tide; at this day length, the decelerative lunar torque could have been canceled by an accelerative torque from the atmospheric tide, resulting in no net torque and a constant rotational period . This stabilizing effect could have been broken by a sudden change in global temperature . Recent computational simulations support this hypothesis and suggest the Marinoan or Sturtian glaciations broke this stable configuration about 600Myr ago, citing the resemblance of simulated results and existing paleorotational data . </P> <P> Additionally, some large - scale events, such as the 2004 Indian Ocean earthquake, have caused the length of a day to shorten by 3 microseconds by affecting the Earth's moment of inertia . Post-glacial rebound, ongoing since the last Ice age, is also changing the distribution of the Earth's mass thus affecting the moment of inertia of the Earth and, by the conservation of angular momentum, the Earth's rotation period . </P> <P> The primary monitoring of the Earth's rotation is performed with very - long - baseline interferometry coordinated with the Global Positioning System, satellite laser ranging, and other satellite techniques . This provides an absolute reference for the determination of universal time, precession, and nutation . </P> <P> There are recorded observations of solar and lunar eclipses by Babylonian and Chinese astronomers beginning in the 8th century BCE, as well as from the medieval Islamic world and elsewhere . These observations can be used to determine changes in the Earth's rotation over the last 27 centuries, since the length of the day is a critical parameter in the calculation of the place and time of eclipses . A change in day length of milliseconds per century shows up as a change of hours and thousands of kilometers in eclipse observations . The ancient data is consistent with a shorter day, meaning the Earth was turning faster throughout the past . </P>

What is the effect of the earth's rotation on day and night