The Aravalli Range is a textbook example of an ancient orogenic belt. Formed during the Precambrian era, it was once a towering range as high as the modern Himalayas. Over hundreds of millions of years, the forces of denudation (weathering and erosion) have worn it down to its present-day status as a series of low hills and ridges. In contrast, the Himalayas, Alps and Rockies were formed during the much later Alpine Orogeny. Geographically, the Aravallis are crucial for India as they act as a barrier against the expansion of the Thar Desert toward the fertile Indo-Gangetic plains.