Centuries are numbered ordinally in English and many other languages.For example, "the 17th century" strictly refers to the years from 1601 to 1700, but popularly refers to be the years 1600 to 1699.A centenary is a hundredth anniversary or a celebration of this, typically the remembrance of an event which took place a hundred years earlier.According to the Gregorian calendar, the 1st century AD/CE started on January 1, 1, and ended on December 31, 100.
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When a fossil is sandwiched between two such volcanic deposits, their potassium-argon dates provide a minimum and maximum age.
In the example below, the bone must date to sometime between 1.75 and 1.5 million years ago.
There is no year zero in this scheme, so the year AD 1 immediately follows the year 1 BC.
This dating system was devised in 525, but was not widely used until after 800.