Relative dating of the pennsylvanian period

The time scale at left is both a reference and a key to the display cases at the museum ­ click on a geologic period to go to that case.

Note that in the United States it is common to break the Carboniferous into two periods, the Pennsylvanian and the Mississippian, as is done in our museum. Andrew Mac Rae for the use of the time scale image and the short essay below.

Earth's history, quite literally, is written on the strata of its rocks, and from observing these layers, geologists have been able to form an idea of the various phases in that long history.

Naturally, information is more readily discernible about the more recent phases, though even in studying these phases, it is possible to be misled by gaps in the rock record, known as unconformities.

Each rock layer that corresponded to a unit of the Geologic Time Chart was identified in a somewhat haphazard manner.

The Paleozoic Era was not identified and included in the developing time chart until 1838, however the Devonian Period of the Paleozoic Era was identified a year earlier in 1837.

Relative time - named subdivisions of the Earth's geology in a specific order (for example, the "Cambrian Period", followed by the "Ordovician Period", and "Silurian Period").

Absolute time is the measurement taken from the same rocks to determine the amount of time that has expired.The Devonian Period of the Paleozoic Era lasted from 417 million years ago to 354 million years ago.It is named for Devon, England where the old red sandstone of the Devonian was first studied.Among the earliest contributions to what could be called historical geology came from the Italian scientist and artist Leonardo da Vinci (1452-1519), who speculated that fossils might have come from the remains of long-dead animals.Nearly two centuries later, stratigraphy itself had its beginnings when the Danish geologist Nicolaus Steno (1638-1687) studied the age of rock strata.

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