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 Greek architecture
Historians divide ancient Greek civilization into two eras, the Hellenic period (from around 900 BC to the death of Alexander the Great in 323 BC), and the Hellenistic period (323 BC to 30 AD). During the earlier Hellenic period, substantial works of architecture began to appear around 600 BC. During the later (Hellenistic) period, Greek culture spread widely, initially as a result of Alexander's conquest of other lands, and later as a result of the rise of the Roman Empire, which adopted much of Greek culture.