THE GEOLOGICAL TIME SCALE [FULL DETAILS]

THE GEOLOGICAL TIME SCALE [FULL DETAILS]

Credit: THE GEOLOGICAL SOCIETY OF AMERICA

How much do you know about the earth?

The Geological Time Scale is a record of the developmental changes which has taken place over a period of billions of years in the Earth.

It depicts the periods of remarkable developments in life (i.e evolution of life), evolution of oceans, basins and continents.

Have you heard of Vasquez Rock?

It is usually represented in the form: eras (eons), periods, epochs and ages.

The Geological Timescale depicts major occurrences which is mostly global and regional. These occurrences are evident some of which include:

a.      Orogenic  activities ( mountain building activities);

b.     Mass extinctions (as in dinosaurs) and appearance of new species;

c.      Continental drifting evidences;

4. Certain species dominant in some places

5. widespread glaciations around the poles

f.       Sea floor spreading

g.     Evolving of life from iron algae to phytoplanktons and zooplanktons up to modern day vertebrates.

It is important to note that the Geological Timescale is not vain; rather it was constructed via scientific principles / evidences stated below:

1. Stratigraphic correlations;

2.     Earth’s rotation;

3.     Physical Observations from fields (field observations);

4.     Fossil records; correlations of stratigraphy;

5.     Earth’s revolution;

6.     Magnetic (Paleo) orientations and

7.     Radiometric dating

The key to understanding how the earth was formed lies in the understanding the Geological Time scale.

geologic  time  scale  is  a  basic  necessity  while  studying  the  geography  of  the  earth.

TERMINOLOGIES YOU NEED TO UNDERSTAND ABOUT THE GEOLOGIC TIME SCALE

EON: refers to the mega unit comprising duration of half a Billion years (or) more time;

ERA: refers to the duration of several Hundred Millions of years;

PERIOD: refers to Hundreds of Millions of years;

EPOCH: refers to the duration of Tens of Millions of years

AGE: refers to a duration of Millions of years in the earth’s history.

FURTHER SUB-DIVISIONS:

The Eons are further subdivided based on Visible lives present (Phanerozoic eon

) and Invisible lives (Cryptozoic eon).

The two Eons were further subdivided into five Eras:

1. CENOZOIC ERA:           65 mya to the present
2. MESOZOIC ERA:                    245 –66.4 mya (Age of Reptiles &Ammonoids)
3. PALAEOZOIC ERA:       540 – 245 mya
4. PRECAMBRIAN / PROTEROZOIC  ERA:   4500 mya – 540 mya.
5. ARCHAEAN ERA:            4500 mya to 2500 mya

IMPORTANT FACTS TO KNOW:

The oldest era of the earth is the Precambrian. It is the period between the formation of the Earth to the beginning of the Cambrian Period. It is worth noting that the  fossil  record  of  Precambrian period  is  very  poor of which the stromatolites is one of them.

Plate motions and tectonic activities are not clearly known in the Precambrian.

Events of Precambrian period are:

1. Life  appeared for the first time on earth

2. Dry and cold climate to warm and moist conditions prevailed on the earth. The Earth experienced climate variation (i.e. Dry and cold climatic condition to warm and moist condition)

3. Tectonic Plates began to move

4. Enrichment of the atmosphere with oxygen

The Precambrian sub-divided into:

          The Archean Era (about 3960-2500 Mya)

          The Proterozoic Era (about 2500-540 Mya)

ACTIVITIES IN THE ARCHEAN ERA

Extensive Orogenesis

The prokaryotes, bacteria and blue-green algae emerged

Formation of Greenstone belts and banded iron ores

         

          Shallow seas appeared.

ACTIVITIES IN THE PROTEROZOIC ERA

Eukaryotic cells and multicellular lives emerged

The Earth experienced warm and moist conditions

The Earth experienced Dry and Cold climate

Soft-bodied marine invertebrates (Earliest known fossils) e.g. Annelids, Sponges, Sea anemones emerged

THE PALAEOZOIC ERA (540 mya - 245 mya)

This is divided into six periods namely:

         

Permian    (about 286  -  245  mya)

Carboniferous    (about 360  -  286   mya) - First coal appeared

Devonian      (about 408  -  360  mya) – This is the age of fish

Silurian    (about 438  -  408  mya)

Ordovician  (about 505  -  438  mya) - This is the age of Graptolites

Cambrian    (about 540  -  505  mya) – This is the age of trilobites. More lives

emerged on Earth in this Period

ACTIVITIES IN THE CAMBRIAN PERIOD

          Sea transgression

          Mild climate

         

          Shelled Marine invertebrates appeared

Brachiopods, sponges, Trilobites, Gastropods, echinoderms, radiolarians, 

appeared

          Floating, Swimming, crawling, clinging and burrowing sea animals appeared

Also evident were: sea cucumbers, starfish, jelly fish, and water scorpions

Plants in existence were only algae (land plants were absent)

THE  ORDOVICIAN PERIOD

ACTIVITIES IN THE ORDOVICIAN PERIOD

Regression of shallow seas

Mild climate

First vertebrates emerged (jawless fishes) while invertebrates dominated

Southern Continents formed a single land mass known as Gondwana Land

First fungi emerged

Marked by high sea levels rise resulting in transgression

Mollusks, cephalopods, crustaceans, corals, bryozoans, graptolites, trilobites, brachiopods and echinoderms, were present and dominated the marine environment.

THE SILURIAN PERIOD

ACTIVITIES IN THE SILURIAN PERIOD

Shell-forming sea animals were in abundance

Vascular Plants appeared on earth

Continents were flooded and flat

Mild climate with stable and warm temperature

Land scorpions, eurypterids and Sea lilies, were predominant

Arthropods dominated the continent

Evolution of modern group of Algae and Fungi

Mass extinction of marine organisms

THE DEVONIAN PERIOD

ACTIVITIES IN THE DEVONIAN PERIOD

Migration of Fishes into the open seas

Folding and mountain-building activities took place

Violent volcanic eruptions and crustal movements

Greater percentage of the land was submerged

Appearance of amphibians and Lunged fishes. This is the age of fishes, rays and sharks

Primitive vascular plants went into extinction while modern day seed producing vascular plants appeared

THE CARBONIFEROUS PERIOD

ACTIVITIES IN THE CARBONIFEROUS PERIOD

Strictly known for coal deposits, Grit stones, and lime stones

Earth experienced highest  atmospheric oxygen levels ever seen on earth

Prominenet fauna were the winged insects

First land vertebrates appeared

Sea invertebrates like Corals, Crinoids, Bryozoans, Foraminifers, Brachiopods, Cephalopods, and Blastoids were in dominance

First Reptiles laid eggs with shells

Prominent flora was Sigillaria

THE PERMIAN PERIOD

ACTIVITIES IN THE PERMIAN PERIOD

Is known for worldwide continental uplift and orogenic movements.

           

Land masses amalgamated into the super continent (Pangaea) - thereby creating the Appalachians.

           

            Palaezoic Plants and invertebrates went into extinction

         

          Extinction of all Trilobites, Blastoids and Graptolites went into extinction

Mass extinctions occurred in this period

           

            Spiriferid brachiopods, ammonoids, foraminifers and bivalves were prevalent

          Cone-bearing Gymnosperms appeared.

MESOZOIC ERA

This is subdivided into three periods viz:

         

Cretaceous            (about 144  -  66.4  mya) - The youngest period in the Mesozoic era

         

          Jurassic                 (about 208  -  144  mya)

Triassic                 (about 245  -  208  mya) – The oldest period in the Mesozoic era

ACTIVITIES IN THE TRIASSIC PERIOD

Appearance of Primitive Mammals

Emergence of the Continents

Terrestrial deposition starts

Marine Invertebrates reduced in population (mass extinction)

Archosaurs occured on land as dinosaurs, Pterosaurs in the air while Ichthyosaurs, Nothosaurs  in  oceans

Formation of red beds

Global climate and ocean circulation was altered

Formation of Gypsum and Salt

Climate was arid

Lizards, modern conifers, first turtles, dinosaurs, cycadeoids, and mammals appeared

Appearance of first mammals and crocodiles

Orogenic activities still continued in some parts

Ceratitic ammonoids were in abundance

Pangaea was still in existence (intact)

ACTIVITIES IN THE JURASSIC PERIOD

Pangaea broke up into Gondwanaland and Laurasia

Dinosaurs that eat green plants existed

Gymnosperms abounded

Palm-like cycads and Ferns abounded

There was a hyper increase in the Atmospheric CO₂

First frogs appeared, also flying reptiles, birds, salamanders, crocodiles, were present

Sponges, starfish, crinoids were abundant   

Various types of Dinosaurs were in dominant

Sea  urchins  were  ubiquitous

THE CRETACEOUS PERIOD

ACTIVITIES IN THE CRETACEOUS PERIOD

Belemnites, Marine Pelecypods, sponges and bivalves were common

Appearance of first primates

Chalk deposits were present

New types of insects evolved

Flying reptiles and toothed birds (Primitive birds) were present

Angiosperms were present

Formation of Rocky Mountains

Various types of dinosaurs were on the land

Various types of crocodiles were on the land

Modern flowering plants were present new types of insects.

Gondwanaland broke up

Echinoids, Ammonites were all over

CENOZOIC ERA (RECENT LIFE)

THIS ERA IS SUBDIVIDED INTO TWO:

Quaternary Era (The age of man)

            Tertiary Era (The age of mammals)

Periods under the Tertiary era:

          Pliocene                (about 05-02 Mya)

          Miocene                (about 25-05 Mya)

          Oligocene                       (about 38-25 Mya)

          Eocene                  (about 55-38 Mya)

          Paleocene              (about 65-55 Mya)

THE PALEOCENE PERIOD

ACTIVITIES IN THE PALEOCENE PERIOD

            First large mammals and Modern  plants appeared

                  

          Alpine orogeny and Himalayan orogeny

THE EOCENE PERIOD

ACTIVITIES IN THE EOCENE PERIOD

            Reglaciation took place in the South Pole

            Appearance of first grasses

          Moderate climate

          Formation of marginal seas

           

            Mammals dominated

THE OLIGOCENE PERIOD

ACTIVITIES IN THE OLIGOCENE PERIOD

Mammals  and  modern  flowering evolved 

First elephants appeared

Carnovires were well pronounced

Warm climate

THE MIOCENE PERIOD

ACTIVITIES IN THE MIOCENE PERIOD

Glaciation took place in Southern Hemisphere

Basaltic flows were evident

Bird families are now distinct

Moderate climate

Grasslands extended

Apes appeared

Modern mammals are now distinct

Horses were assorted

Volcanic activities took place

Bird families became distinct

THE PLIOCENE PERIOD

ACTIVITIES IN THE PLIOCENE PERIOD

Appearance of Homo habilis

Beginning of Ice Age

Uplift of the Continent / Mountain building

Huge carnivorous animals were dominant

Hominids (I.e humans like primates) appeared

Cool (but) dry climate

Seas were restricted

Appearance of a lot of the present generation of mammals and mollusks

QUATERNARY ERA (THE AGE OF MAN)

This is subdivided into:

PLEISTOCENE PERIOD                    (about 1.6-0.01 Mya)

HOLOCENE PERIOD            (about 10000 - recent)

THE PLEISTOCENE PERIOD

ACTIVITIES IN THE PLEISTOCENE PERIOD

Known as Ice age

Modern Humans evolved

Deserts were formed

Advancement and retraction of ice

Many large mammals went into extinction

Climate was Glacial

A lot of Human populations were destroyed by volcanic eruptions

Beginning of Human Stone Age

Mass extinctions of mammals as a result of ice and anthropological activities

HOLOCENE PERIOD

ACTIVITIES IN THE HOLOCENE PERIOD

Drastic habitat changes

Human civilization was sporadic

Agricultural activities increased with crude implements

Paleolithic lifestyle starts (This is subdivided into Lower, Middle, and Upper periods), Mesolithic, and Neolithic

PLEASE NOTE THESE

Copper Age           (about 3500 BC)

Bronze Age           (about 2500 BC)

Iron Age                (about 1200 BC)