GEOLOGICAL TIMESCALE

Dr. P. Sarathbabu M.Sc. B.Ed. Ph.D

Department of Geology

Acharya Nagarjuna University

Geologic time scale:

The time span of earth’s history is about 4,500

million years. It is roughly represented by the column

of sedimentary rocks now present on the earth.

In this record the time elapsed during the formation

of unconformities is missing. The unconformities are

however, important because they subdivide the

geological time into smaller units.

On this basis a standard Geological Time Scale has

been prepared which is used universally for the

correlation of rock formations.

• The geological time scale is subdivided into ‘eons’ and ‘eras’.

• Each eon divided into eras

• Each era comprises a number of ‘periods’, which in turn, are subdivided into ‘epochs’.

• Eon: It is a major unit and extremely long period of time (thousands of years)

• Era: The second major unit of geological time are called ‘eras’

• Period : Each era has been subdivided into smaller units called ‘periods’

• System :A succesionof rocks deposited during a period constitutes a ‘system’

The geological timescale can be

broadly classified into two periods: the

Precambrian super eon and the

Phanerozoic eon.

1 Precambrian

Hadean Eon

Archean Eon

Proterozoic Eon

2 Phanerozoic Eon oPaleozoic Era

oMesozoic Era

o Cenozoic Era

• Archaean era = Azoic era (Zoë = life; Azoic=lifeless)

• Precambrian era = Proterozoic (protero=very early,

meaning an era with very early life,

which is not recorded as fossils)

Primary era = Palaeozoic era (palaeo = ancient or old,

meaning the era with first important life is

recorded as fossils)

Secondary era = Mesozoic era (Mesos=middle,

meaning an era with life, which is neither old

nor recent)

Tertiary era = Cenozoic era (ceno = recent, meaning

an era with recent life)

Geologic Time Scale Eon Era Period Starting Age (Ma)

Phanerozoic

Cenozoic Quaternary

65 Tertiary

Mesozoic

Cretaceous

248 Jurassic

Triassic

Paleozoic

Permian

540

Pennsylvanian

Mississippian

Devonian

Silurian

Ordovician

Cambrian

Precambrian - Proterozoic 2500

Precambrian - Archean 3800

Precambrian – Hadean 4500

http://en.wikipedia.org/wiki/File:Pangea_animation_03.gif

http://en.wikipedia.org/wiki/File:Pangea_animation_03.gif

The Present is the Key to the Past

Thank You