Africa: The long voyage of an ancient continent.

25/05/2020

Africa is a very old continent indeed, but it was not immune to change, and looked completely different in the past. Read about continents, life and ice ages in Africa, in this introduction for "geodummies" and everybody who is interested in the nature of Africa. 

Text: Kathelijne Bonne

It is Africa Day today, I just discovered. That requires immediate action, especially as Africa is my favorite continent. There seems to be a 'day' for everything, we can hardly keep up with it. Floating on this new hype of days-to-commemorate-something, I take this opportunity to talk on the natural history of Africa. 

Africa's natural history is incredibly diverse and fascinating, just as any other aspect of the continent itself. 

What is Africa, geologically speaking? 

It is a continent, one large single block of land areas, surrounded by oceans. Africa has come a very long way. It has been a single entity since Cretaceous times, the very warm period of geological time when sea levels were very high, and dinosaurs still roamed the Earth. Africa has been 'alone' since then, (since about 100 million years ago, in the middle of the Cretaceous). 

Before, Africa was connected to other continents. Through the action of plate tectonics, i.e. the phenomenon responsible for the 'moving of continents', the other landmasses that were once connected to Africa, drifted away, one by one. 

Africa was thus connected to South America, southern Europe, India, Madagascar and Antarctica. It formed one huge landmass, better known as the supercontinent named Gondwana. Africa lay right in the middle of Gondwana. I am tempted to say it was the heart of Gondwana, but it doesn't sound scientific. None of Africa's vast stretches of coastline that are so appreciated today, existed then. Without any interruption, the plateaus of Africa ran into the juxtaposed landmasses. 

Gondwana existed for an enormous time-span of almost 500 million years. You must know, continent movements seem to undergo cycles. Sometimes they are all united into one supercontinent, as was the case with Gondwana. And during other times, the continents are spread across the globe, like today. Imagine what it would mean to humankind, if all these continents would join again. And it will happen.

The Earth with Gondwana, 420 million years ago (image: Fama Clamosa / CC BY-SA 4.0)
The Earth with Gondwana, 420 million years ago (image: Fama Clamosa / CC BY-SA 4.0)

The birth of Gondwana

How did Gondwana come to existence? Before the end of the Precambrian (~540 million years ago), there were many small continents distributed across the globe. They steadily moved - or drifted - towards each other. I quickly add here a note on how life forms were at that time, so you can get a feel of the incredible time spans we talk about. Life was nothing like today, to say the least. At that time (end of the Precambrian, and start of the Phanerozoic) there was only life in the seas. 

But it was an exciting time because life forms suddenly became more complex, animals evolved and diversified rapidly. There was no life on the land yet. 

The land areas of Gondwana, and Africa, still remained barren for quite a long time. 

Let's return to the smaller continents that moved towards each other. As one small continent joined the other, the landmass gradually became bigger. As such, Africa itself consists of three, maybe four, separate, ancient continents that merged together. Some parts of these ancient blocks lie at the surface and you can walk on them in many parts of Africa. They are known as the West African, Congo and Kalahari 'shields'. More small continents joined and the landmass became bigger. 

High mountains and huge river systems

The 'collisions' to form the supercontinent Gondwana obviously unfolded very slowly, but when enough time passes, it leads to the formation of mountains. Many collisions had led to the formation of Gondwana. Therefore, this supercontinent was crisscrossed by huge mountain chains. These mountains were much greater and stretched over much larger areas than any mountain chain today. In some scientific papers, researchers refer to it as the Trans-Gondwana mountain system. 

Furthermore, great rivers swept across the supercontinent, and slowly but steadily the great mountains weathered down, eroded, and the landscape became smoother and less dramatic. 

Great Carboniferous ice age

Long times passed, and finally, after about 400 million years ago, also the land became occupied by life and the planet became green. Nevertheless, Africa, as a part of Gondwana, lay in a very southern position, near the South Pole. And during Carboniferous times, our planet was plagued by an ice age. Signs and traces of this great ice age can be found in many places of Africa, India and South America. In another article, I will explain how important these traces have been for the science of geology. But here I leave it as a side-note. 

All bad weather eventually passes, and warmer climates dominated the scene after the Carboniferous ice age. 

Fractures and rift systems

Later (during the Mesozoic Era), long fault lines started to fracture the continent of Gondwana. These fractures deepened, forming large depressions, sometimes occupied by lakes, similar to the lakes in the East African Rift valley today. Such fractures are lines along which continents will break apart. And so it happened. 

Gondwana broke apart along the lines that are now the coastlines of Africa and the other continents. 

Madagascar, India and Antarctica got disconnected from Africa first, during the Jurassic Period. Then, a bit later, the South American continent broke away, moving westward. The Indian and Atlantic oceans steadily became wider, separating the once united continents, which slowly moved to their current positions. Africa was now alone as a continent and living creatures started their own, separate evolution. 

Craddle of humankind

But Africa's journey doesn't stop here. Many things happened on each of the continents since then. The Earth and life are in a constant flux, and nothing stays the same. Today, a new great rift system is actively forming, creating the incredible natural environment and landscapes of East Africa. Coincidence or not, that part of Africa is also the cradle of humankind. 


Check out our separate category on Africa, to see the other articles we have on African topics.