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.
Classical Greece
This century is essentially studied from the Athenian outlook because Athens has left us more narratives, plays, and other written works than the other ancient Greek states. From the perspective of Athenian culture in Classical Greece, the period generally referred to as the 5th century BC extends slightly into the 4th century BC. In this context, one might consider that the first significant event of this century occurs in 508 BC, with the fall of the last Athenian tyrant and Cleisthenes' reforms. However, a broader view of the whole Greek world might place its beginning at the Ionian Revolt of 500 BC, the event that provoked the Persian invasion of 492 BC. The Persians were defeated in 490 BC. A second Persian attempt, in 481–479 BC, failed as well, despite having overrun much of modern-day Greece (north of the Isthmus of Corinth) at a crucial point during the war following the Battle of Thermopylae and the Battle of Artemisium. The Delian League then formed, under Athenian hegemony and as Athens' instrument. Athens' excesses caused several revolts among the allied cities, all of which were put down by force, but Athenian dynamism finally awoke Sparta and brought about the Peloponnesian War in 431 BC. After both forces were spent, a brief peace came about; then the war resumed to Sparta's advantage. Athens was definitively defeated in 404 BC, and internal Athenian agitations mark the end of the 5th century BC in Greece.