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.
Greece in the 5th century BC
The period of the 5th century BC in classical Greece is generally considered as beginning in 500 and ending in 404, though this is debated. This century is essentially studied from the Athenian viewpoint, since Athens has left more narratives, plays and other written works than the other Greek states. If one looks at Athens, our principal source, one might consider that this century begins in 510, with the fall of the Athenian tyrant and Cleisthenes's reforms. If one looks at the whole Greek world, however, we might place its beginning at the Ionian revolt in 500, that provoked the Persian invasion of 492. The Persians (called "Medes") were finally defeated in 490. A second Persian attempt failed in 481-479. The Delian League then formed, under Athenian hegemony and as Athens' instrument. Athens' excesses caused several revolts among the allied cities, which were all put down by force, but Athenian dynamism finally awoke Sparta and brought about the Peloponnesian War in 431. After both sides were exhausted, a brief peace occurred, and then the war resumed to Sparta's advantage. Athens was definitively defeated in 404, and some internal Athenian agitations ended the 5th century in Greece.