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Mesolithic period

(Encyclopedia)Mesolithic period mĕzˌəlĭthˈĭk [key] or Middle Stone Age, period in human development between the end of the Paleolithic period and the beginning of the Neolithic period. It began with the end o...

synodic period

(Encyclopedia)synodic period sĭnŏdˈĭk [key], in astronomy, length of time during which a body in the solar system makes one orbit of the sun relative to the earth, i.e., returns to the same elongation. Because ...

Mississippian period

(Encyclopedia)Mississippian period: see Carboniferous period. ...

Pennsylvanian period

(Encyclopedia)Pennsylvanian period: see Carboniferous period. ...

Carboniferous period

(Encyclopedia)Carboniferous period kärbənĭfˈərəs [key], fifth period of the Paleozoic era of geologic time (see Geologic Timescale, tablegeologic timescale, table), from 350 to 290 million years ago. The pl...

Jurassic period

(Encyclopedia)Jurassic period jərăsˈĭk [key] [from the Jura Mts.], second period of the Mesozoic era of geologic time, lasting from 213 to 144 million years ago. At the start of the Jurassic most of the contine...

Devonian period

(Encyclopedia)Devonian period dĭvōˈnēən [key], fourth period of the Paleozoic era of geologic time between 408 and 360 million years ago (see Geologic Timescale, tablegeologic timescale, table). It was named (...

Paleolithic period

(Encyclopedia)Paleolithic period pāˌlēəlĭthˈĭk, –lēō–, pălˌ– [key] or Old Stone Age, the earliest period of human development and the longest phase of mankind's history. It is approximately coexten...

Silurian period

(Encyclopedia)Silurian period sĭlo͝orˈēən, sī– [key] [from the Silures, ancient tribe of S Wales, where the period was first studied; named by the British geologist R. I. Murchison], third period of the Pal...

Ordovician period

(Encyclopedia)Ordovician period ôrdəvĭshˈən [key] [from the Ordovices, ancient tribe of N Wales], second period of the Paleozoic era of geologic time (see Geologic Timescale, tablegeologic timescale, table) fr...