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.
2nd century BC
The 2nd century BC started the first day of 200 BC and ended the last day of 101 BC. It is considered part of the Classical era, although depending on the region being studied, other terms may be more suitable. It also considered to be the end of the Axial Age. In the context of the Eastern Mediterranean, it is referred to as the Hellenistic period.