Ki tudja, h a földtörténetben miért harmadidőszak a harmadidőszak, és miért a következő miért negyed?

Negyedidőszak: A kifejezést először Giovanni Arduino olasz természetbúvár használta az 1700-as években, amikor az Alpok és az attól délre eső területek földtanát vizsgálva a képződményeket négy sorozatra bontotta, és a negyedikbe („quatro ordine”) a Pó-síkság alluviális üledékeit sorolta.

(Az alföldek a legfiatalabb földrajzi képződmények)

A harmadidőszak is hasonlóan kapott nevet (ezt csak angolul találtam meg): The term Tertiary was first used by Giovanni Arduino during the mid-18th century. He classified geologic time into primitive (or primary), secondary, and tertiary periods based on observations of geology in northern Italy. Later a fourth period, the Quaternary, was applied. In the early development of the study of geology, the periods were thought to correspond to the Biblical narrative, the rocks of the Tertiary being thought to be associated with the Great Flood. In 1828, Charles Lyell incorporated a Tertiary Period into his own, far more detailed system of classification. He subdivided the Tertiary Period into four epochs according to the percentage of fossil mollusks resembling modern species found in those strata. He used Greek names: Eocene, Miocene, Older Pliocene and Newer Pliocene. Although these divisions seemed adequate for the region to which the designations were originally applied (parts of the Alps and plains of Italy), when the same system was later extended to other parts of Europe and to America, it proved to be inapplicable. Therefore, the use of mollusks was abandoned from the definition and the epochs were renamed and redefined.