Универсальный англо-русский словарь. Академик.ру. 2011.
Hirnantian — The Hirnantian is the seventh and final internationally recognized stage of the Ordovician Period of the Paleozoic Era. It was of short duration, lasting about 1.9 million years, from 445.6 ± 1.5 to 443.7 ± 1.5 Ma (million years ago). The early… … Wikipedia
Ordovician — Period 488.3–443.7 million years ago … Wikipedia
Chronostratigraphy — is the branch of stratigraphy that studies the age of rock strata in relation to time. The ultimate aim of chronostratigraphy is to arrange the sequence of deposition and the time of deposition of all rocks within a geological region, and… … Wikipedia
