2. Geologic Time Scale
A record of the life forms and
geological events in Earth’s
history.
Scientists developed the
timescale by studying rock
layers and fossil worldwide.
Radioactive dating helped
3.
4. • GIVING TIME A NAME
• The largest sections are
called “eons”.
• “Eons” are divided into
“eras” (the 2nd largest
section).
•“Eras” are divided into
“periods”.
• ‘Periods’ are
divided into ‘epochs”
5. Eons
• Largest, most general
division
of time.
• 2 Eons
• The eons are: Cryptozoic
(Precambrian) eon and
Phanerozoic eon.
• Precambrian and
Phanerozoic eon both
consists of three eras as
shown in the figure.
All life forms were long
assumed to have
originated, and
therefore, all earlier
rocks were grouped
together.
Started when
Precambrian time ended
by which conditions
were set for the
explosion of life.
6. Eras
• Each Eon is broken up
into Eras.
Major eras in Earth’s
history:
• Archean (4600 mya -
2500 mya)
• Proterozoic (2500 mya -
540 mya)
• Paleozoic (540mya -
250mya)
