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.
Helladic chronology
Helladic chronology is a relative dating system used in archaeology and art history. It complements the Minoan chronology scheme devised by Sir Arthur Evans for the categorisation of Bronze Age artefacts from the Minoan civilization within a historical framework. Whereas Minoan chronology is specific to Crete, the cultural and geographical scope of Helladic chronology is mainland Greece during the same timespan (c.3200–c.1050). Similarly, a Cycladic chronology system is used for artifacts found in the Aegean islands. Archaeological evidence has shown that, broadly, civilisation developed concurrently across the whole region and so the three schemes complement each other chronologically. They are grouped together as "Aegean" in terms such as Aegean civilization.