Distinguish among eons, eras, periods, and epochs, using specific examples.

In a particular context, “epoch” can refer to a particular point of time characterized by a particular event/series of events.

While “era” refers to a period of time characterized by events in a chronological order.

Thus, an “era” can encompass more than one “epoch”.

“Period” can refer to a short interval of time or a very long interval of time.
For example:

“Eon” refers to an indefinitely long time. Eon is presumed to consist of at least 2 eras.

Eras, Eons, Epochs and Periods are the division and subdivisions of geological time scale based on the changes in the  geography, geology, climate and other characteristics of the earth.

The sequence of the various divisions depends on the length of each unit of time relative to each other.

sequence of time period is as follows:

Eons > Eras > Periods > Epochs

1.Eons-The longest division of time scale which lasts for billion of years.

            Geologists recognised three major Eons as:  

                                               Phanerozoic Eon (570-present)

                                               Proterozoic Eon (2500-570 mya)

                                                Archean Eon (3800-2500 mya)

2.Eras-eras are the subdivision of Eons which froms the second longest division of time scale. Eras can lasts for tens to hundreds miliion of years.

                  These are recognised as:

                           Coenozoic Era (66 mya-present)

                            Mesozoic Era (66-240 mya)

                             Paleozoic Era (240-570 mya)

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3. Periods- Subdivion of time scale which is relatively shorter in time length.

periods can last for tens to  million of year

Geologists have divided eras into periods-

Coenozoic Era

                               Quaternary-(present)- Evolution of humans

                                Tertiary- Mammals diversified

Mesozoic Era

                               Cretaceous-extiction of dinosaurus

                               Jurassic-Dinosaurus diversified

                               Permian- age of mammals

Paleozoic Era

                              Pennysylvian-First reptiles

                              Mississipian-seed ferns

                              Devonian-first amphibians

                              Slurian-first land plants

                              Ordovician - metazoan diversification

                              Cambrian-first fishes

4.Epochs- subdivision longer than an age but shorter than a period .

                  Epoch can last for tens of million years.

phylogenetic tree is the tree of life or evolution tree. it shows the different branches of evolution. the sequence goes like tissues - coelom - backbone - endoskeleton - segmentation

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