The geological time scale outlines Earth's history divided into eras, including the Precambrian, Paleozoic, Mesozoic, and Cenozoic, each containing various periods and epochs characterized by significant biological developments. Key highlights include the rise of trilobites and early aquatic life in the Paleozoic, the dominance of reptiles in the Mesozoic, and the emergence of mammals and flowering plants in the Cenozoic. The Quaternary era, the most recent, features two epochs marked by glaciation and the rise of modern humans.

1. Geological Time Scale
1
Geological Time scale :
Era Age in
millions
Major division
Or
Period
Epochs
Quaternary
1.8 Holocene
3 – 1.8 Pleistocene
Tertiary
5.3 – 3
Neogene
Pleiocene
23 – 5.3 Miocene
34 – 23
Paleogene
Oligocene
56 – 34 Eocene
65 – 56 Palaeocene
Mesozoic
65 – 145 Creataceous
145 – 200 Jurassic
200 – 253 Trassic
Paleozoic
OR
“Ancient life “
253 – 299 Permian
299 – 359 Carboniferous
359 – 418 Devonian
418 – 443 Silurian
443 – 488 Ordovisian
488 – 582 Cambrian
Proterozoic 500 – 1600
Archaeozoic 1600 – 3800
Azoic 4200 – 4600
Azoic and Archaeozoic Era : Azoic was used as early as 1846 by a geologist named Adams. Due to the controversy
over evolution, "Azoic" was replaced, by 1900, in most usages by the term "Archaean" or "Archaeozic".
Proterozoic Era : The first advanced single-celled, eukaryotes and multi-cellular life. stromatolites reached their
greatest abundance .
Palaeozoic Era : The Paleozoic Era comes from the Greek palaios "old" and zoe "life", meaning "ancient life".
 Cambrian : abundance of trilobites., marine algae
 Ordovician : abundance of trilobite's, Graptolites, tebrates, marine algae.
 Silurian : Graptolites disappear at the end: first fishes ; probably first land plants appears.
 Devonian : abundance of corals, Brachiopoda ; first amphibians and lung-fishes ; shark .
 Carboniferous : Many non-flowering plants: first repltils appear.
 Permian : trilobites disappear at the end of this period.
Mesozoic Era : The Mesozoic Era is an interval of geological time from about 252 to 66 million years ago. It is also
called the Age of Reptiles.

2. Geological Time Scale
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 Trassic : Ammonites, reptiles and amphibia abundant , Arid climate. Gymnosperms dominant and declined towards
the end.
 Jurassic : Ammonites abundant, first birds, flowering plants. Continent fairly high.
 Cretaceous : Gaint reptiles and ammonites disappear at the end. Flowering plant become numerous. First bird and
snakes appearance.
Tertiary or Cenozoic Era : This “Modern life Era” is the “age of mammals”.
 Palaeogene : It is divided into 3 epochs.
 Paleocene – Himalaya-I uplift, folding in Rockies Mountain, Appearnce of Angiosperm. Rise of archaic
mammals.
 Eocene – climate became warmer, rise of flowering plants.
 Oligocene – Alps, Himalaya – II uplift, Archaic mammals extinct.
 Neogene : It is divided into 2 epochs.
 Miocene – Andes, Himalaya – III uplift, cooler climate, appearance of grasses,
 Pliocene – Himalaya – IV uplift, volcanic activity, origin of man, evolution of horse, elephant, camels almost
like modern species.
Quaternary Era : It is recent Era divided into 2 epochs.
 Pleistocene : Periodic glaciation, rise of herbs, Extinction of mammals ; first human social life.
 Holocene or Recent : climate warmer, end of last ice age. Rise of modern man.