The gradual movement of tectonic plates has resulted in the formation of orogenic mountain ranges. These mountain ranges have developed on border zones where two tectonic plates have slowly collided. The process has taken millions of years.

When two tectonic plates collide, their edges are folded. This creates a series of folded mountains. As tectonic plates continue their movement to this day - albeit at a relatively slow pace of a couple of centimeters per year - all orogenic mountain ranges are still developing, and will continue to grow taller over time. 

When the age of a folded or orogenic mountain range can be measured in tens of millions of years, the mountain range is called a young orogenic mountain range. Examples of such mountain ranges include all the well-known mountain ranges of Central and Southern Europe: the Alps, the Pyrenees, the Apennines, the Carpathian Mountains, and the Balkans. 

The American Cordillera is the longest chain of orogenic mountain ranges in the world. The Cordillera consists of many different mountain ranges, such as the North American Rocky Mountains and the South American Andes.

The young mountain ranges of the American Cordillera were formed approximately 60 million years ago. When most people think of mountains, they usually visualize something along the line of the vistas of the Rockies and the Andes: tall mountains with sharp peaks and steep slopes. These are the features common to all young orogenic mountain ranges.

When the age of a folded mountain range is measured in hundreds of millions of years, it is considered an old orogenic mountain range. An excellent example of this kind of a mountain range is found on the border of eastern Europe and Asia. This mountain range, the Ural Mountains, was formed over 300 million years ago. Another example of an old orogenic mountain range are the Appalachian Mountains of the eastern United States.

Old orogenic mountain ranges have been subject to external or exogenous processes for hundreds of millions of years. These processes, such as ice, water, weathering, and erosion, have transformed the looks of these mountain ranges significantly. As a result, old orogenic mountain ranges are characterized by their low mountains and gentle slopes.

In the beginning of a mountain range's formation, the mountains are subject to wear through processes like erosion and weathering. These processes wear out the exterior layers of the mountains, which consist of weaker types of rock than the interior layers. After hundreds of millions years of wear, only the strongest, central parts of the mountains are left.

The picture on the right shows the Appalachian Mountains, which are an old orogenic mountain range in the eastern United States. Exogenous processes have worn down the peaks until they have become flat and round.