There are so many realities that we take for granted the presence of the sky above us, the rising and setting of the sun and the matter present in this universe including the landmass and the oceans.
If you were asked, how many continents are in our world today, you will not hesitate to reply, Seven. But two hundred years ago, the shape of earth was not the same. All continents were joined together, as one big landmass. The scientists refer to it as PANGAEA - 'PAN' means 'whole' and 'GAEA' refers to the Greek goddess of the earth. The reason, why scientists including Archaeologists and Anthropologists, know this to be a fact is, because they have studied rock formations and flora (plants) and fauna (animals) of the different continents. They found for instance, that animals and plants found in India, are also found in Eastern Africa.
The elephants and dinosaurs are prime example. With the large oceans separating the areas, there is-no other way, the animals could have crossed from one place to another. And mountains on the eastern coast of America are made of the same type of rock found in Scotland and Scandinavian countries. So, the scientists presume that once upon a time, these places were joined together, and then because of the pressure of heat under the surface of the earth, Pangaea broke up and the oceans currents caused the broken pieces, to drift away in different directions.
The continents are still moving today but so slowly, approximately two centimeters a year, that we don't see any significant difference. Although the continents may look like one big piece of land on a map, but they are actually made up of many tightly joined pieces called plates. Sometimes when the heat under the surface of the earth makes the plates move, the land on top of the plates moves as well, causing earthquakes and tidal waves. At such a time, many towns and cities are destroyed and many islands and coastlines disappear under water.
When the disturbance is over, you may see that the geographical terrain of the place may change. Scientists believe that changes in the earth's surface may be the reason, why some animals became extinct i.e., disappeared for ever. For example, if a major earthquake destroys all the trees in the area, animals which used to eat leaves from trees will face two choices, either to adapt to eating grass or to slowly die out. This may have happened to the dinosaurs or it may have been that a major earthquake or a crashing meteorite killed all the dinosaurs in one stroke. Nobody knows for sure. It is still a mystery, why they became extinct.