A new timescale has recently been established for human mitochondrial DNA (mt DNA) lineages, making mt DNA at present the most informative genetic marker system for studying European prehistory.Here, we review the new chronology and compare mt DNA with Y-chromosome patterns, in order to summarize what we have learnt from archaeogenetics concerning five episodes over the past 50,000 years which significantly contributed to the settlement history of Europe: the pioneer colonisation of the Upper Palaeolithic, the Late Glacial re-colonisation of the continent from southern refugia after the Last Glacial Maximum, the postglacial re-colonization of deserted areas after the Younger Dryas cold snap, the arrival of Near Easterners with an incipient Neolithic package, and the small-scale migrations along continent-wide economic exchange networks beginning with the Copper Age.The Western (Roman Catholic and Protestant) Christian churches use the Gregorian tables while many Eastern (Orthodox) Christian churches use older tables based on the Julian Calendar.Thus, the civil date of Easter depends upon which tables - Gregorian or pre-Gregorian - are used.The statement that Easter Day is the first Sunday after the full moon that occurs next after the vernal equinox, is only an approximate statement of the actual ecclesiastical rules.The full moon involved is not the astronomical Full Moon but an ecclesiastical moon (determined from tables) that keeps, more or less, in step with the astronomical full Moon.The Council decided to keep Easter on the same Sunday throughout the Christian world.To fix incontrovertibly the date for Easter, and to make it determinable indefinitely in advance, the Council constructed tables to compute the date.
It also regulates the ceremonial cycle of the Roman Catholic and Protestant churches.
The ecclesiastical rules are: Easter can never occur before March 22 or later than April 25.
The Gregorian dates for the ecclesiastical full moon are determined using the tables in the Papal bull Inter Gravissimas.
In 1582, Christopher Clavius and a council working at the direction of Gregory XIII (Pope of the Roman Catholic Church) completed a reconstruction of the Julian Calendar producing new Easter tables.
The new calendar was issued in February in the papal bull called "Inter gravissimas".