Cryptic (geology)
The Cryptic era is an informal term for the earliest geologic evolution of the Earth and Moon. It is the oldest (informal) era of the Hadean eon, and it is commonly accepted to have begun close to 4533 million (about 4.533 billion) years ago when the Earth and Moon formed. No samples exist to date the transition between the Cryptic era and the following Basin Groups era for the Moon (see also Pre-Nectarian), though sometimes it is stated that this era ended 4150 million years ago for one or both of these bodies. Neither this time period, nor any other Hadean subdivision, has been officially recognized by the International Commission on Stratigraphy.
Dating creation
According to Censorinus (quoting Varro), the second period ("mythikón") lasted from 2137 to 776 BC, or if Censorinus' own dates are used: 2376 BC to 776 BC, or finally if Castor's: 2123 BC to 776 BC. Ovid, however, dated the start of the ("mythikón") period to the reign of Inachus, who he dated 400 or so years "after" the flood of Ogyges, meaning around 1900–1700 BC, but agreed with Varro that the "mythikón" ended during the first Olympiad (776 BC). See Ages of Man for more details about Ovid's chronology. Another ancient date for the start of the "mythikón" (mythical) period is found preserved in Augustine's "City of God" xviii.3, which dates it to 2050 BC. The final period according to Censorinus and Varro, the "historikón" (historical) era, began from 776 BC (the first Olympiad) to their own time: