wv<br >i G eoogy usesthe scentfcmethodto<br > explain natural aspects of the earth--<br > for example， how mountains form or<br > why oil resources are concentrated in<br > some rocks and not in others. This<br > chapter briefly explains how and why the earth s sur-<br > face， and its interior， are constantly changing. It re-<br > lates this constant change to the major geological<br > topics of interaction of the atmosphere， water and<br > rock， the modern theory of plate tectonics and geo-<br > logic time. These concepts form a framework for the<br > rest of the book. Understanding the "big picture"<br > presented here will aid you in comprehending the<br > chapters that follow.<br >