We have found an empirical law for the variation of the length ofthe Earth's day with geologic time employing Wells's data. Weattribute the lengthening of the Earth's day to the present cosmicexpansion of the Universe. The prediction of law has been found tobe in agreement with the astronomical and geological data. The dayincreases at a present rate of 0.002 sec/century. The length of theday is found to be 6 hours when the Earth formed. We have also founda new limit for the value of the Hubble constant and the age of theUniverse.