50. million. years.

The hills are alive? How islands came to rise atop the Himalayas
Dan Vergano, USA Today, September 29, 2008

Home to hundreds of the world's loftiest mountains, including Everest, the Himalayas take their name from a Sanskrit word meaning "the Abode of Snow." But parts of these lofty mountains were once sun-kissed isles glistening in a now-vanished sea.
That's according to an upcoming study that highlights this geological reminder of impermanence on Earth.

"The islands are actually tipped on their sides," says the University of Houston's Shuhab Khan, lead author of the study scheduled for release in the October Geological Society of America Bulletin. "So you can walk — it's incredible — from the bedrock to the seafloor sediment of these islands."

What scraped the islands off the seafloor and lifted them up to the top of northern Pakistan was the collision between the continental crusts of India and Asia. Khan and his colleagues show the collision that built the Himalayas came 50 million years ago in their analysis, which ties together satellite maps, field geology, mineralogy, chemistry and magnetic dating data from the Kohistan-Ladakh bloc, the one-time archipelago dating to the time of the dinosaurs.

The collision of India with Asia continues to this day, with the Indian subcontinent essentially diving beneath the Asian one, lifting up the Tibetan plateau. Geologists have long agreed the Kohistan bloc islands represent the contact point between the two continents, but until now they weren't certain how they made their journey to the Himalayas. . . .

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