Geological Time Scale

Geological Time Scale and Namibia

The below geological time scale begins some 4.5 billion years ago and represents the development of the earth, its seas and land masses. The Paleo-Maps cover a period beginning 650 million years ago showing the development of the land masses beginning with the ancient continent of Rodina and continuing through to 50 million years in the future, showing, where it is thought the land mass of Africa, and Namibia, will be situated should tectonic plate movement continue at the present level.

 

Between 4,000 and 2,500 million years ago the early plate tectonic movements in the earth's crust began to form the first land masses. In southern Africa the Kaapvaal Craton stabilized as long ago as 3,000 Ma, and the Zimbabwe Craton had stabilised by 2,600 Ma. By 1,300 Ma ago these two Cratons had connected with the Congo and Kalahari Cratons, and the land mass known as Rodinia was beginning to form.

 

What's in a name: Gondwana derives its name from an area situated in Central India, meaning Land of the Gonds, where a 'tribe' of people known as the Gonds lived. Also in this area of India is a geological feature that was formed in the early Palaeozoic to early Mesozoic eras and is referred to as the Gondwana Beds. During the latter part of the nineteenth century the Austrian geologist Edward Suess, suggested that, on the basis of comparative geological evidence, the continents of Africa - Australia - India and South America had once formed a super continent which he named Gondwana. OK, so if one 'says' Gondwana, it literally means Land of the Gonds Land, or Gonds-Land Land. It would appear that Gondwana is the more correct of the two.

 

Plate-tectonic movement caused the land mass to increase and also move southwards that by the Early Cambrian Period some 500 million years ago Gondwana had grown into a great continent comprising of what is now referred to as Africa - Antarctica - Australia - India - Madagascar - South America - and at one time even included the American State of Florida and part of Southwest Europe, with the southern areas straddling the polar region. From 320 to 270 million years ago the Great Gondwana Ice-Age covered Namibia. Glaciers scoured the ancient rock formations and during the melt floods moved enormous amounts of boulder debris and sediments that in places would settle to be thousand of metres thick . During this time the great inland Gai-As sea covered much of southern and western Namibia and spread into what is now South America. The discovery of Mesosaurus fossils in both Brazil and Namibia have helped to support the theory of Continental Drift . There were later times when vast deserts covered much of Namibia and extensive volcanism. Gondwana began to break about 130 million years ago and the two new continents of Africa and South America began to drift apart. See the below Paleo Maps created by Christopher R. Scotese for a better understanding of the earth's plate movements from 650Ma ago and into the future 50Ma to see an equatorial Namibia.

 

The Air That We Breath: The oldest known of fossils in the world are of the green-blue algae known as cynobacteria that lived at the edges of the ancient oceans as early as 3,500 million years ago. These simple algae increased to be the dominant life force on the planet for most of the Eon of time known as the Proterozoic, and derived their energy from the sun's rays by the process of photosynthesis. 3,000 Ma ago the earth's atmosphere was rich with carbon dioxide and devoid of oxygen, but over a period of 1 billion years the activity of these small algae had increased the atmosphere's oxygen content to about 20% which in turn allowed for more complex life forms to evolve. These algae with their glutinous sheaths as protection grew in colonies and carpeted the sea bed. Grains of sand would cling to the sheath's and eventually block the sun's light from them. The algae's survival response was that of growing up through the layer of grains in order that they could continue with the process of photosynthesizing. This pattern of early life continued over hundreds of millions of years and eventually led to the building of the great carbonate mountain chains. The fossilized remains of these algae 'constructions' are named Stromatolites and represent the some of the oldest of all fossils, and can be found in Namibia.

650 Ma ago

The Super Continent of Rodinia began to form 1,100 million years ago, and by the Late Neoproterozoic (650 million years ago) it was starting to divide into the land masses that would become known as Baltica and Laurentia, with Gondwana positioned in the southern latitudes.

Namibia:  The Otavi Mountain lands were formed (stromatolites and oncolites) by algae growth along with early marine life deposits that laid to depths of up to 5 kilometres. The fossilized Stromatolites and Oncolites that can be found in the area are between 830 to 760 million years old.

356 Ma ago

Early Carboniferous: The super continent of Pangaea began to form as the Palaeozoic oceans between Euramerica and Gondwana began to close. The ice cap at the south polar region grew, and the vertebrates being fish evolved while on the land plants were the dominant life form.

Namibia: As the southerly parts of the super-continent moved further south he ice cap was moving northwards and ice sheets were beginning to form across southern Africa.

306 Ma ago

Late Carboniferous: The continents (of modern) North America and Europe collided with the southern continent of Gondwana to form the western half of Pangaea. Great ice sheets covered much of the southern hemisphere while the vast coal swamps formed in the equatorial regions of Pangaea.

Namibia: was near to the South-Pole experiencing the 'Dwyka' Ice-Age that lasted from 320 to 270 million years ago. Glaciers scoured the land's rocky surface as they moved to the sea carrying rock debris with them. As the Ice-Age ended the sea level rose. Sediments were deposited on the 'Dwyka" rocks. Mud-stones and shale beds were formed. Fossils of this period that have been found in Namibia are those of ancient fish and shell fish. Glossopteris plants were spreading along the banks of rivers and delta

255 Ma ago

Permian: Gondwana moved northwards. The climate warmed. In the northern and southern hemisphere large deserts covered western Pangaea. Reptiles were spreading across the land, but at the end of the Palaeozoic 99% of life perished. There was an extinction event.

Namibia: The great lake Gai-As covered an area stretching from the Karoo in South Africa across southern Namibia (Karasburg - Keetmanshoop) and into what is now Brazil. The first land reptiles to return to the water were Mesosaurus and they swam in this great inland sea. In the north of Namibia there were great forests of Cordaites trees similar to those that can be seen at the Petrified Forest .

Mass Extinction

Event

250 million years ago the life forms on earth were subject to the greatest, known of, extinction event. 95% of marine life forms died, 70% of land creatures died and plant life forms suffered equally. It is thought that as the northern continent of Laurasia collided with Gondwana to form Pangaea that great land upheavals and marine regressions were experienced. A dramatic increase in 'greenhouse' gasses such as methane all contributed to the mass extinction of the ancient flora and fauna.

Triassic Period: The Archosaurs dominated the food chain and were the ancestors of the Dinosaurs, modern day crocodilians, and birds.

195 Ma ago

Early Jurassic: South-East Asia moves northwards and The Great Tethys Ocean separates the 'new' northern continents from Gondwana. On land the Dinosaurs were beginning their rule across Pangaea.

Namibia: The ancient rocks of the Omingonde Formation were beginning to be covered over by the deposits know as the Etjo Formation. Early dinosaurs such as the Ceratosauria that left their tracks at Otjihaenamaparero and Massospondylus that left its tracks on top of the Waterberg Plateau wandered

 

Namibia: The Etjo Formation was being deposited on top of the Omingonde Formation

152 Ma ago

Late Jurassic: The super continent of Pangaea began to separate in the Middle Jurassic period. By the Late Jurassic the Central Atlantic Ocean was between the north west African coast and the eastern seaboard of North America.

Namibia: Is part of great desert that covers most of Gondwana

94 Ma ago

Late Cretaceous: It was in this period that the South Atlantic Ocean opened as the continents of Africa and South America moved away from each other. Africa also was moving northwards. Antarctica and Australia were still joined. India separated from Madagascar and began to move northwards on a collision course with Eurasia.

North America was connected to Europe.

Namibia: The Mesosaurus fossil finds in eastern Brazil and southern Namibia played an important role in helping to prove the theory of Continental Drift.

Today

A Modern World: Presently has well defined climatic zones, and we are in the latter stages of leaving an Ice-Age. Global warming is a natural progression. The addition of so called 'greenhouse gases may accelerate the warming.

Namibia: It appears that Namibia will experience a dryer climate and increased desert areas. The new 'Buzz-Word' is Global Warming.

 

The continents are once again drifting together and a new Pangaea will eventually be formed.

50 Ma into the future

The Future: Should 'continental drift' continue at the present rate, the above is a projection of what the earth may look like in 50 million years time. The Atlantic Ocean widens. Africa moves northwards and collides with Europe closing the Mediterranean Sea. Australia collides with South-East Asia, while California slides northwards towards Alaska.

Namibia: Lays on the Equator and could be covered with tropical rain forests. (some wait)

 

Plate tectonic maps and Continental Drift animations by C.R. Scotese, PALEOMAP Project. (www.scotese.com)

In geological terms the earth's time scale is divided into four Eons, beginning with the Hadian, Archaean, Proterozoic and the latter being the Phanerozoic Eon in which we live can be seen below to be the shortest in time span of the four Eons. The word Phanerozoic is derived from the Greek and means "clear evidence of life".

Each of the Eons is divided into Eras, which in turn are sub-divided into Periods and then into Epochs.

 

As stated above, early life began in the seas about 3,500 million years ago in the Archean Era, but it was not until the Paleozoic Era, about 570 million years ago that a profusion of marine invertebrates developed such as cephalopods, corals, gastropods, trilobites and worms. The early fish were invertebrates having their bodies within 'armour casings'.  The first vertebrates appeared about 500 million years ago and fish evolved into creatures having a bone skeletal frame and became the dominant vertebrate. About 410 million years ago certain species of fish developed into amphibians and began to colonize the land. It was about 360 million years ago that the early reptiles evolved and they in turn began to displace the amphibians as the dominant land species.

 

Note: The time scale used is as determined by the  International Committee on Stratigraphy (ICS)

Acknowledgements and further reading:  E1,  E2, G1, G2, G3, M2, W1, W2

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Geological Time Scale

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