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.
Ancient history
The period between AD 320–550 is known as the Classical Age, when most of North India was reunited under the Gupta Empire (c. AD 320–550). This was a period of relative peace, law and order, and extensive achievements in religion, education, mathematics, arts, Sanskrit literature and drama. Grammar, composition, logic, metaphysics, mathematics, medicine, and astronomy became increasingly specialized and reached an advanced level. The Gupta Empire was weakened and ultimately ruined by the raids of Hunas (a branch of the Hephthalites emanating from Central Asia). Under Harsha (r. 606–47), North India was reunited briefly.