Hadean
The Hadean () is a geologic eon of the Earth pre-dating the Archean. It began with the formation of the Earth about 4.6 billion years ago and ended, as defined by the ICS, 4 billion years ago. , the ICS describes its status as ""informal"". Geologist Preston Cloud coined the term in 1972, originally to label the period before the earliest-known rocks on Earth. W. Brian Harland later coined an almost synonymous term, the "Priscoan period", from "priscus", the Latin word for "ancient". Other, older texts simply refer to the eon as the Pre-Archean.
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.