Cryptic eraとは 意味・読み方・使い方

The Cryptic era is an informal term that refers to the earliest geologic evolution of the Earth and Moon. It is the oldest era of the (informal) Hadean eon, and it is commonly accepted to have begun close to 4567.17 million (about 4.6 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.