The Himalayan range, topped by 29,035-foot Mount Everest, the tallest mountain in the world, is one of the largest and most distinct geographic features on the earth's surface. The range, running northwest to southeast, stretches 1,400 miles; varies between 140 miles and 200 miles wide; crosses or abuts five different countries—India, Nepal, Pakistan, Bhutan, and the People's Republic of China; is the mother of three major rivers—the Indus, Ganges, and Tsampo-Bramhaputra; and boasts over 100 mountains that exceed 23,600 feet.

Formation of the Himalayas

Geologically speaking, the Himalayas and Mount Everest are relatively young. They began forming over 65 million years ago when two of the earth's great crustal plates—the Eurasian plate and the Indo-Australian plate—collided. The Indian subcontinent moved northeastward, crashing into Asia, folding and pushing the plate boundaries until the Himalayas were eventually over five miles tall. The Indian plate, moving forward about 1.7 inches per year, is being slowly pushed under or subducted by the Eurasian plate, which obstinately refuses to move. As a result, the Himalayas and the Tibetan Plateau continue to rise about 5 to 10 millimeters each year. Geologists estimate that India will continue moving northward for almost a thousand miles over the next 10 million years.

Peak Formation and Fossils

As two crustal plates collide, heavier rock is pushed back down into the earth's mantle at the point of contact. Meanwhile, lighter rock such as limestone and sandstone is pushed upward to form the towering mountains. At the tops of the highest peaks, like that of Mount Everest, it is possible to find 400-million-year-old fossils of sea creatures and shells that were deposited at the bottom of shallow tropical seas. Now the fossils are exposed at the roof of the world, over 25,000 feet above sea level.

Marine Limestone

The peak of Mount Everest is made up of rock that was once submerged beneath the Tethys Sea, an open waterway that existed between the Indian subcontinent and Asia over 400 million years ago. For the great nature writer John McPhee, this is the most significant fact about the mountain:

When the climbers in 1953 planted their flags on the highest mountain, they set them in snow over the skeletons of creatures that had lived in the warm clear ocean that India, moving north, blanked out. Possibly as much as twenty thousand feet below the seafloor, the skeletal remains had turned into rock. This one fact is a treatise in itself on the movements of the surface of the earth. If by some fiat I had to restrict all this writing to one sentence, this is the one I would choose: The summit of Mt. Everest is marine limestone.

Sedimentary Layers

The sedimentary rock layers found on Mount Everest include limestone, marble, shale, and pelite; below them are older rocks including granite, pegmatite intrusions, and gneiss, a metamorphic rock. The upper formations on Mount Everest and neighboring Lhotse are filled with marine fossils.

Main Rock Formations

Mount Everest is composed of three distinct rock formations. From the mountain base to the summit, they are: the Rongbuk Formation; the North Col Formation; and the Qomolangma Formation. These rock units are separated by low-angle faults, forcing each one over the next in a zigzag pattern.

The Rongbuk Formation includes the basement rocks below Mount Everest. The metamorphic rock includes schist and gneiss, a finely banded rock. Intruded between these old rock beds are great sills of granite and pegmatite dikes where molten magma flowed into cracks and solidified.

The complex North Col Formation, which begins about 4.3 miles up the mountain, is divided into several distinct sections. The upper section is the famous Yellow Band, a yellow-brown rock band of marble, phyllite with muscovite and biotite, and semischist, a slightly metamorphosed sedimentary rock. The band also contains fossils of crinoid ossicles, marine organisms with skeletons. Below the Yellow Band are alternating layers of marble, schist, and phyllite. The lower section is composed of various schists made of metamorphosed limestone, sandstone, and mudstone. At the bottom of the formation is the Lhotse detachment, a thrust fault that divides the North Col Formation from the underlying Rongbuk Formation.

The Qomolangma Formation, the highest section of rock on the summit pyramid of Mount Everest, is made of layers of Ordovician-age limestone, recrystallized dolomite, siltstone, and laminae. The formation starts about 5.3 miles up the mountain at a fault zone above the North Col Formation, and ends at the summit. The upper layers have many marine fossils, including trilobites, crinoids, and ostracods. One 150-foot layer at the bottom of the summit pyramid contains the remains of microorganisms, including cyanobacteria deposited in shallow warm water.