Geologic Time Scale
regional scale, the smallest
stratigraphic is a single stratum or layer
which is called a bed. These beds are
grouped together into members. All
beds in the member have the same
lithology.
Scientists have spent the last few centuries putting
together this geologic time scale.
Geologic Time Scale
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It is a system of chronological dating that
relates the rocks on our planet to time.
The development of this has required
extensive work in both relative and absolute
dating of rocks.
It has required stratigraphic correlation of
lithologies, feces, and fossils located all across
our planet.
It has required international cooperation
among scientists of all backgrounds working
to develop a standardized system for
recognizing, defining, and naming time
intervals of the past.
Its purpose is to relate the rocks we see on
Earth in the present to time intervals that
transpired in the past.
The formal geologic time scale used by
scientists is known as the International
Chronostratigraphic Chart.
International Chronostratigraphic Chart
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It includes not just names of the time intervals
but also their absolute ages, measured in
millions of years and determined from
absolute dating methods.
It is produced by a collaborative academic
organization known as the International
Commission on Stratigraphy. The commission
revises the chart almost every year, and
sometimes, multiple times a year. The changes
aren’t merely to improve the aesthetics, but
incorporates new information, data and
knowledge into the chart.
The golden spikes that is present on this chart
are actually a real thing. In geology, golden
spikes are driven into strata to mark the
boundaries between time intervals. These also
mark the location of the Global Stratigraphic
Section and Point for a boundary.
This chart deals with both rock and time.
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Stratigraphic Unit
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It is a volume of rock which can be
traced laterally across a region.
Each stratigraphic unit receives a
name. Some units can be traced
laterally across a local region or area.
Others can be correlated across the
globe.
There is a hierarchical system for
naming, organizing and assigning
stratigraphic units. On a local or
Chronostratigraphic
Unit
Eonothem
Erathem
System
Series
Stage
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Eon (longest)
Era
Period
Epoch
Age (shortest)
Chronostratigraphic Unit
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Geochronologic Unit
It corresponds to Geochronological
Units or time intervals.
These are bodies of rock that exist
today.
Geochronologic Unit
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It is a time interval that transpired in the
past.