Tectonic plates

These are the six continents, as we know them. They are oceans apart. Yet if you look at their shapes… ...they seem to... ...fit together, like pieces of a jigsaw puzzle! Perhaps you have looked at a world map and noticed this before? During the early 20th century, scientists thought that this was a coincidence, and that the continents weren’t moving at all.

But today we know better! This is what we think the Earth looked like about 300 million years ago. All of the Earth’s land mass was connected as one big supercontinent: Pangea. Then, as millions of years passed by, the continents drifted apart… ...and right now they happen to be located in the places where we are used to seeing them. Is this hard to believe for you too, as it was for most scientists a hundred years ago?

How is it possible that something as large, solid, and heavy as a continent, can drift around like this? To understand that, we need to look inside the Earth for a moment. This is what the Earth would look like, if we cut a piece out of it and peeked inside. The crust is a thin layer of solid rock. The crust is floating on top of the mantle, which is a thick viscous layer of hot rock.

The mantle is heated by the Earth’s core, creating convection currents, that cause the mantle to move, really slowly. The crust itself is like a hard rocky shell surrounding the Earth. But it’s broken shell, divided into sections: large plates. Seven really large ones and many smaller ones. We call them: tectonic plates. ...

The tectonic plates follow the movements of the mantle, drifting slowly but steadily, a few centimeters or so in a year. But they drift in different directions. So what happens then, where the plates meet, at the plate boundaries? Well, three different things can happen here. Here, two plates are colliding, forming a convergent boundary.

This is how many of the mountain ranges in the world are formed. The second kind of plate boundary is when two plates move away from one another – a divergent boundary. On land, where the crust is thicker, this creates a canyon with steep edges, a rift valley. On the ocean floor, where the crust is thin, a divergent boundary can rip it open, and magma comes up. The magma is cooled by the water, hardens, and forms a long range of underwater mountains: an ocean ridge.

If instead, the plates are moving past each other, we have a transform boundary. Sometimes plates along a transform boundary get stuck on each other. Pressure and friction builds up between the plates as they try to pass one another, and then suddenly, they jerk free, causing the ground to shake. Just as near the other boundary types, this is a place where earthquakes are common. … Today, there is plenty of evidence for the tectonic plate theory. One of several methods that scientists used to figure this out, was comparing the remains of old plants and animals, fossils.

There are fossil traces found, from the same species, from the same time period, but on different continents. Areas which are now separated by oceans, were once part of the same continuous forests! It is actually possible to find traces from even further back in time, even before Pangea was formed. Because the tectonic plates have apparently been drifting around for billions of years, forming several supercontinents, which have later disintegrated again. So, it’s no coincidence the continents appear to fit together – they really are the pieces of a giant jigsaw puzzle.