FILE PHOTO: A panoramic view of Earth
Credit: Reuters Photo
If a continuous land mass is a continent, we would legitimately wonder why Great Britain or New Zealand or even Japan are not continents… So, the definition gets modified a bit: A large, continuous land mass
Hmm… ok… but what’s ‘large’ (it’s one of those unclear words that your composition teacher won’t like, I assure you)? Japan has 14,125 islands. That sounds pretty large, doesn’t it? Well, actually, no… All those islands only cover 378 sq kms. And continuous? What about all those island countries in our neighbourhood, like Sri Lanka? The thing is, continents are defined more by convention than by any strict criteria. (For example, some people even club Asia and Europe together and talk about Eurasia) Cultural similarities come into it as well as other things. Great Britain does not have distinctive geological or cultural features that would define it as a separate continent.
But maybe this ambiguous definition is a good thing; because over the millennia, the continent that your descendants live on just might change even if the people don’t move!
It was in the early years of the 20th century that scientists began to theorise that continents, land masses, could have moved around. The earth is around 71% water and these land masses get pushed around. How do we know this? Well for one thing, look at a map. Doesn’t the east coast of South America look like it could almost fit into the west coast of Africa if it were a jigsaw puzzle? Then there’s the distribution of ancient fossils (e.g. Mesosaurus fossils on separate continents), rocks, and mountain ranges across continents that are eerily similar. Coal deposits in Pennsylvania are similar in composition to those across parts of Europe. And so are the cultural artifacts. People in East Central Africa (around Tanzania) apparently used grinding stones like the ones your grandmother would have used.
It is now believed that 320 to 195 million years ago, a single land mass — a super continent existed where almost all the land on earth was joined together. Scientists call this Pangaea. Surrounding it was a sea called Panthalassa. Like many terms we use today, ‘Pangaea’ comes from the Greek. Pan means ‘all’ and Gaea means the ‘earth’. Pangaea likely never included all of the continents at any one time so if you look at a map of Pangaea, you’ll find significant areas missing. It’s interesting to see how the east coast of Africa seems to have been joined to the west coast of India until it probably broke off around 200 million years ago and drifted north bumping into the rest of the Asian continent around 50 million years ago. (A collision that caused the Himalayas to bump out).
Pangaea existed for more than 100 million years and during that time, species could and did travel over land and then evolve in their new habitats to adapt to local conditions. Maybe that’s why the African elephant is so different from the Asian one?
How then did Pangaea split up? Earth’s outer crust is made up of large plates of rock. These float on weaker layers of partially melted rock on the earth’s mantle below. Heat from the earth’s core heats up the layer of rock above and this heat rises upward and pushes the cooler rock downward creating a churning that moves the layers. Much churning later, pieces of land move. About 80 million years ago, North America separated from Europe, Australia began to drift away from Antarctica, and eventually, India broke away from Madagascar and collided with Eurasia.
The plates are still moving at an approximate rate of 5 inches per year. Playing around with models and creating likely scenarios, scientists believe that over time, the Pacific Ocean will close up and Australia, North America, Africa, and Eurasia will come together in the Northern Hemisphere. We’ve already given that new super continent a name — “Amasia.” In time to come, there’ll be just 3 continents: Antarctica, South America and Amasia.
For now, though, we have 7 continents: Asia, Africa, North America, South America, Antarctica, Europe, and Australia in order of size. Antarctica doubles in size every winter as the ice hardens and land area increases. Our world is just fascinating, isn’t it? We change and so does our planet.