Introduction

The chapter opens by linking back to what you have already studied — the interior of the earth. From the world map you are familiar with, you know that continents cover 29 per cent of the earth's surface, and the remaining 71 per cent lies under oceanic waters. That basic fact is the starting point.

But here is the deeper idea: the positions of the continents and ocean bodies, as they appear on the map today, have not always been the same. In the past, they were arranged differently. And it is now a well-accepted fact that they will not keep their present positions in the future either. The map you see is only a snapshot of a moving picture.

This raises a chain of questions. What were the positions of the continents and oceans in the past? Why and how do they change their positions? And even if we accept that they have changed and are still changing, how do scientists actually know this? How have they determined the earlier positions of landmasses and ocean basins?

These are the questions this chapter sets out to answer. The chapter will explore the evidence and reasoning that let scientists reconstruct where continents and oceans once stood, and understand the forces that keep shifting them.