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.
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.