Geological Time Scale

Origin of organisms on earth in various time period.

1. GEOLOGICAL TIME SCALE

2. The total life span of the earth from the time of its origin is called Geological time. The geological time scale is a record of the life forms and geological events in earths history. Aim of time scale by studying earth layers and fossils worldwide. Radio active dating helped determine the absolute divisions in the time scale and it helps understand the evolution of earth

3. Available evidence indicate that the age of earth is about 5 billion years. Change of earth classified the following manner 1. Changes Occur Suddenly: Catastrophism a. Catastrophism : the principle that states that all geologic change occurs suddenly. b. Supporters of catastrophism thought that Earth’s features, such as mountains and seas, formed during sudden events called catastrophes. 2. Changes Occur Gradually: Uniformitarianism a. About 250 years ago, James Hutton established a principle that is now known as uniformitarianism . b. Uniformitarianism : the idea that the same geologic processes that shape Earth today have been at work throughout Earth’s history. c. The principle also states that the average rate of geologic change is slow and has remained relatively constant over time.

4. The largest portions are called “ eons ” Eons are divided into “ eras ” Eras are divided “ periods ” Periods are divided into “ epochs ”

5. Earth’s 4.6-billion-year history is divided into four eons: Hadean , Archean , Proterozoic , Phanerozoic The Hadean , Archean , and Proterozoic eons together are called Precambrian time . Precambrian time makes up almost 90% of Earth’s history. The Phanerozoic Eon, the present eon, is divided into three eras: the Paleozoic , Mesozoic, and Cenozoic . The periods of the Cenozoic , the present era, are further divided into epochs.

6. Geological time scales consists of 7 major eras Azoic Archaeozoic Proterozoic Palaeozoic Mesozoic Coenozoic Psychozoic

7. The geological time scale. Image by Jonathan R. Hendricks.  This work is licensed under a  Creative Commons Attribution- ShareAlike 4.0 International License

8. No many changes were observed in the eons of Hadean , Archean and Proterozoic . But the Phanerozoic eon is divided into many eras Mesozoic Coenozoic Psychozoic

9. It is the era of ancient life. It had duration of about 370 million years (Starting about 600 & ending by 230 million years ago). This era was age of higher invertebrates, fishes and amphibians. The Palaeozoic era is divided into many periods Periods are

10. The rocks were documented and discovered first in this period. Duration is 75 million years Its was started the melting of glaciers and rise the sea level Fossils of this period is Algae, fungi, bacteria, protozoan, sponges, coelenterates, annelids molluscs echinoderms, The primitive arthropods are plenty and predominant constituted about 50% of total fauna This painting is a 1997 illustration of an assortment of Cambrian era creatures by D.W. Miller.

11. Duration is 65 million years. The first vertebrates Ostracoderms appear during this period. Fossils of Algae, Corals gastropods & branchiopods are dominant. The corals, snails, clams, Nautilus and echinoderms made their appearance during this period. Ordovician Period fossils

12. Duration is 35 million years. The Land Plants (ferns) & Air breathing invertebrates appeared in this period. Placoderms and Sea lilies were predominant. Silurian period fossils

13. Duration is 45 million years. It is described as Age of fishes. Ostraderms are predominant in this period. First land vertebrate amphibians & Ammonites group of Cephalapods were appeared . Land Plants are predominant. Ammonites fossils Fish fossils

14. Duration is 25 million years. It has dense forests, coal, oil, gas, lead, zinc, gold, silver, gypsum and rock salts are formed during this period. Salamander like amphibians appeared Sharks and Sea lilies were predominant. Sea lilies fossils Other fossils from Mississippian period

15. Duration is 25 million years. It has dense insects, few dragon flies with longer wing span (30 inches). In addition the amphibians are high and dominant. First reptiles namely stem reptiles appeared. Mississippian and Pennsylvanian periods are together called Carboniferous period because of rich formation of coal on this earth . Dragon fossils First Millipedes

16. During this period greater changes of Climate and topography Climate very cold and drier Dense of hard wood plants and freshwater fish New genera of beetles dragon and may flies were appeared. Also first appearance of reptiles during this period.

17. It is called period of middle life (between Primitive Palaeozoic & advanced Coenozoic animals). Duration of this era is 150 million years. Reptiles are predominant during this period. Hence it is called Golden age of Reptiles . Era witnessed the rise and fall of reptiles and the origin of birds and origin of mammals. It has three period

18. It is first period of Mesozoic era. Duration of this period is 60 million years. Climate was very harsh and dry Dinosaurs and Pterosaurs originated during this period Egg laying mammals was originated Some of the primitive amphibians are extinct during this period.

19. It is second period of Mesozoic era. Duration -30 million years The climate was warm and humid. Dinosaurs multiplied and dominated Toothed birds and insectivores appeared Archaeopteryx, the fossil connecting link was discovered. Archaeopteryx- connecting link between reptiles and birds

20. It is third period of Mesozoic era. Duration -60 million years Dinosaurs and toothed bird become extinct Morden birds and Archaic mammals a re originated.

21. The C enozoic era represented up to the present . It is age of Mammal. Man appeared during this era. It has two periods namely 1. Tertiary 2. Quaternary The Giant Mammals of the Cenozoic Era

22. Era Traditional Periods New Periods Epochs Cenozoic Era Quaternary Period Neogene Period Holocene Epoch Pleistocene Epoch Tertiary Period Pliocene Epoch Miocene Epoch Paleogene Period Oligocene Epoch Eocene Epoch Paleocene Epoch

23. Period Epoch Continental Positions New Mammals N e o g e n e Pliocene Africa closes off the Mediterranean Sea North and South America join at Panama The Geography of the earth similar to today First hominids-human ancesters Miocene Africa is pushing into Europe-forms the Alps Arctic becomes covered with ice Horses,camels,and rhinos Beaver-like animals many apes and other primates

24. P a l e o g e n e Oligocene Australia separates from Antarctica India crashes into Asia-forms Himalayans Antarctica is covered by glaciers Sea levels are low Dogs, cats, and pigs toothed whales Eocene Europe and North America separate Bats Elephant ancestors Whales Eohippus-the first horse Paleocene Europe is joined with North America Australia is joined with Antarctica India a land unto itself Atlantic Ocean is forming The condylarths -ancestors of modern hoofed herbivores Rodents The first Primates

25. https://www.digitalatlasofancientlife.org/learn/geological-time/geological-time-scale / https:// www.wahpeton.k12.nd.us/ourpages/auto/2015/8/20/53494933/U2%20L4%20Notes.pdf https://www.fossils-facts-and-finds.com / Reference

26. Thank you For any Clarification Contact; Dr . T. RAMESH Assistant Professor of Zoology PG & Research Department of Zoology Vivekananda College Tiruvedakam [phone] [email protected]