Tectonic plates shift, and some can even dive under other tectonic plates. We call the process of one plate moving beneath another subduction.

Oceanic parts of plates, like what we find in the Atlantic, are generally heavier and subduct more easily. That's why new crust which forms under the sea doesn't last as long as crust on land does. So subduction destroys large oceans and reunites continents. For instance, Europe and North America are moving away from each other now, but, in the future, there's a good chance that subduction might start again and close all of the Atlantic!

Think of the continents as being much less dense material than the stuff (the mantle) that they're floating on, like a bunch of air mattresses in a swimming pool. The air mattresses get carried around by the wind and currents in the pool. Sometimes they bunch together, and sometimes they all float separately. Similarly, the continents get shoved around (either by "currents" in the mantle, or the tugging of plates caused at subduction zones--where plates sink).

Over Earth's history, sometimes continents (which are parts of plates) clump together (Pangea, for example), and sometimes they're separate, like today.

Enjoy studying plate tectonics!

Pangaea is not the only supercontinent that Earth has seen throughout its lifetime . Geologists aren't exactly sure how many we've had, but most geologists agree that there have been at least 4 throughout Earth's history. Once plate tectonics started on our Earth, it has continuously pushed and pulled the continents apart. Since plate tectonics is still happening, this means that there will be another supercontinent in the future . Right now, the Atlantic ocean is growing and the Pacific ocean is shrinking. This means that in the future, North America may smash into Asia - some geologists call this continent "Amasia". The west coast of the US and the east coast of China may become a new mountain range like the Himalayas. However, we don't know for certain, and lots of scientists are still researching this.

Tectonic plates are in the earth just below the crust. Their movement causes the crust to move -- this changes the position of the continents, and oceans. Depending which direction the plates move they might cause continents to collide.

Earth scientists model the plate movement to predict how the continents will be positioned in the future. They would all have to move towards each other for another supercontinent to form. Although it would take a long time to make another supercontinent because they only move a few inches per year!

A new supercontinent is forming now. Africa is moving northward into Europe, Australia is moving northwest into Asia, and North America is moving north toward the Arctic Ocean, and in the process colliding with Asia in Siberia and with Europe in the north Atlantic. This leaves out South America and Antarctica, of which South America is moving west and will tear away from North America, and Antarctica is just sitting there over the south pole, but the other continents will become one big continent in the next few tens of millions of years.

Scientists have written about this - a new super-continent like Pangea might form in 250 million years.

There's a wikipedia article about this: Pangaea Ultima