Goelogic Time Scale - History of Life on Earth

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The Geologic Time Scale is a tabular representation of the major divisions of the Earth’s history. The time intervals are divided and described from the longest to the shortest as EONS, ERAS, PERIODS and EPOCHS. Each period has an approximated time frame and characterized by distinctive features (events and organisms).



The Geologic Time Scale (GTS)
A. Four eras - Precambrian; Paleozoic; Mesozoic; Cenozoic
B. Periods under the Paleozoic era - Cambrian, Ordovician, Silurian, Devonian, Carboniferous, Permian
C. Periods under the Mesozoic era - Triassic, Jurassic, Cretaceous
D. Periods under the Cenozoic era - Tertiary and Quaternary

The Geologic time is divided into four large segments called Eons:
Hadean, Archean, Proterozoic and Phanerozoic.

The Phanerozoic is divided into Eras: Paleozoic, Mesozoic, and Cenozoic.
Extinction events and appearance of new life forms characterized the divisions among Eras.
Smaller divisions, called Periods, characterized by a single type of rock system, make up each Era.
Some Periods are further divided into smaller time frame called Epochs.

CAMBRIAN EXPLOSION is the belief that there was a sudden, apparent explosion of diversity in life forms about 545 million years ago. The explosion created the complexity of multi-celled organisms in a relatively short time frame of 5 to 10 million years. This explosion also created most of the major extant animal groups today.

The start of the Cambrian was characterized by the breaking up of supercontinent Gondwana into smaller land masses opening up new environmental niches where organisms can colonize and specialize.

Memory Aid / Mneumonic Technique to memorize GTS :

Eras: Precambrian, Paleozoic, Mesozoic, Cenozoic:
* Please Pay My Children!

Periods: Cambrian, Ordovician, Silurian, Devonian, Mississippian, Pennsylvanian, Permian, Triassic, Jurassic, Cretaceous, Tertiary, Quaternary:
* Cold Oysters Seldom Develop Many Precious Pearls, Their Juices Congeal Too Quickly.
* Cows Often Sit Down Carefully. Perhaps, Their Joints Creak

Epochs of Cenozoic Era: Paleocene, Eocene, Oligocene, Miocene, Pliocene, Pleistocene, Holocene (or Recent):
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Precambrian Archean, Proterozoic


What are the evidences that suggest that we are entering / have entered a new epoch?

A new proposed Epoch, the Anthropocene.

- derived from the Greek and means the “ recent age of man ”
- interval of geologic time, (2.6 million years ago to the present), characterized as the time in which the collective activities of human beings (Homo sapiens) began to substantially alter Earth's surface, atmosphere, oceans, and systems of nutrient cycling.
- denote the present time interval, in which many geologically significant conditions and processes are profoundly altered by human activities.

These include changes in:
erosion and sediment transport ,
the chemical composition of the atmosphere, oceans and soils,
environmental conditions.

Fossils , Fossil Type and Fosilization
Dating Fossils : Relative Dating and Absolute Dating

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