The Definite Seventh Day

Can a definite day be observed by all the inhabitants of the earth? This, of course, depends upon the proper answer to another question; viz., Is there such a thing as a definite day of the week, or month, or year, to the whole human family? If there is, all can observe it; if there is not, then chronology itself is thrown into confusion by the indefiniteness of dates which necessarily ensues. On what ground, then, is it asserted that the reckoning of a definite day by the whole family of man is an impossibility?