Passage II

Himalayan Garnets

[1]

When geologist, Elizabeth Catlos, began gathering garnets in the Himalayan Mountains in the late 1990s, most scientists had a fairly rigid understanding of the mountain range’s history. [A] It was commonly held that the Himalayas had formed approximately 55 million years ago when India drifted north on a layer of semimolten rock, collided with Asia. The collision forced one tectonic plate into the other, crumpling the land where the plates met. The resulting mountain range, one of the longest in the world, stretches 1, 500 miles across six countries and features many impressive mountains. Although the Himalayan range was thought to have remained relatively unchanged over these tens of millions of years, Catlos was surprised to discover that some of the garnets she had collected formed less than that many years ago. [B]

[2]

Garnets are gemstones with a crystal structure. They are formed many miles beneath the surface of the earth, where high pressures and temperatures allows them to crystallize. These gemstones are really good in geologic dating. [C] Resistant to chemical change after they crystallize, scientists can analyze the gemstones to determine the temperature and pressure of the earth when the garnets formed Such analyses are possible because garnets also contain monazite, a rare mineral that is easily dated. This allows scientists to identify the garnets’ approximate age. And the earth’s conditions when the gemstones formed.

[3]

The dating of Catlos’s garnets, as well as analysis of the pressures and temperatures encoded in their structure, indicates that they were not formed by a single collision, as was previously thought. Rather, it seems that India has continued to push northward into Asia. According to new estimates, the mountain range as we know it today most likely underwent major changes as recently as five million years ago. Incredibly, as one of Catlos’s colleagues notes, “Geologically, the present Himalayan range front was formed just yesterday.” [D]