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.
Hyborian Age
The word "Hyborian" is derived from the legendary northern land of the ancient Greeks, Hyperborea, and is rendered as such in the earliest draft of Howard's essay "The Hyborian Age." Howard described the Hyborian Age taking place sometime after the sinking of Atlantis and before the beginning of recorded ancient history. Most later editors and adaptors such as L. Sprague de Camp and Roy Thomas placed the Hyborian Age around 10,000 BC. More recently, Dale Rippke proposed that the Hyborian Age should be placed further in the past, around 32,500 BC, prior to the beginning of the last glacial period. Rippke's date, however, has since been disputed by Jeffrey Shanks who argues for the more traditional placement at the end of the ice age.