Mount Everest, also known as Sagarmatha or Chomolungma, is the world’s highest peak. Its physical composition holds a surprising secret, as it is not solely made of the hard, volcanic, or continental rocks one might expect. Instead, the layers that form its bulk tell an ancient story of a tropical marine environment.
The Main Geological Layers
The structure of Mount Everest is not a single uniform mass but a stack of distinct geological units, or strata, thrust over one another. The lowest sections are composed primarily of high-grade metamorphic rocks, forming the base of the massif. These rocks, part of the Rongbuk Formation, include gneiss and schist that were intensely altered by heat and pressure deep within the Earth’s crust.
Metamorphic rocks like gneiss and schist were originally sedimentary or igneous rocks that recrystallized due to the forces of mountain building. They show characteristic banding and foliation, demonstrating the squeezing they endured. Interspersed with these basal layers are intrusions of igneous granite, which formed when magma cooled and solidified within the surrounding rock.
Moving upward, a distinctive feature known as the Yellow Band slices across the mountain’s face. This band, highly visible to climbers, is a layer of metamorphosed sedimentary rock, including dolomite and marble. It gets its color from iron oxides, which stain the calc-silicate minerals a yellowish-brown hue. This intermediate layer sits roughly between 24,600 and 26,000 feet, marking a clear transition in the mountain’s composition.
The summit pyramid, the top 1,000 feet of Everest, is composed of the Everest Formation, also known as the Qomolangma Formation. These rocks are predominantly gray limestone and shale, which are types of sedimentary rock formed from the accumulation and cementation of particles. The presence of these specific rock types at the apex of the planet provides the greatest clue to Everest’s surprising origin.
Evidence of Marine History
The existence of limestone and shale at the mountain’s peak is highly unusual for a continental mountain range and points directly to its past as a seafloor. Limestone, in particular, often forms in warm, shallow marine environments from the calcium carbonate remains of ancient sea life. This geological context suggests that the materials forming the summit were deposited in a vast ocean.
Specific evidence for a marine past is preserved within the summit rocks in the form of fossils. Geologists have collected samples of the gray limestone containing the remains of ancient sea creatures. These fossils include fragments of crinoids, which are marine animals related to starfish, as well as brachiopods and trilobites.
The presence of these marine organisms, dating back to the Ordovician period approximately 450 million years ago, confirms the oceanic origin of the summit rocks. The sedimentary layers of the Everest Formation were once accumulated debris and skeletal remains on the floor of the ancient Tethys Ocean. Finding these remnants of tropical sea life at the highest point on Earth demonstrates the dynamic nature of the planet’s surface.
Formation through Tectonic Collision
The mechanism for lifting ancient ocean floor materials nearly 30,000 feet into the atmosphere is the process of plate tectonics. Mount Everest and the entire Himalayan range are the result of a continental collision that began approximately 50 million years ago. This event started when the Indian tectonic plate began moving northward, eventually crashing into the Eurasian plate.
Before the collision, the Tethys Ocean separated the two landmasses, and the sediments accumulating on its floor would ultimately become the rocks of Everest. When the continents met, the Indian plate, carrying relatively light continental crust, was unable to subduct fully beneath the Eurasian plate. Instead, the compressional force caused the crust to buckle, fold, and thicken.
This collision forced the ocean floor sediments—the future Everest Formation—to be scraped up and thrust high into the air. Geologists refer to this uplifting mechanism as thrust faulting, where huge slices of rock are pushed up and over adjacent layers. The complex, folded layers of rock visible on the mountain are scars from this persistent geological squeezing.
The continental collision did not end millions of years ago; the Indian plate continues to push into the Eurasian plate at a rate of roughly 4 to 5 centimeters per year. This ongoing tectonic activity means that Mount Everest is still actively rising, growing a few millimeters taller each year. The mountain’s composition is therefore a direct record of the geological forces on Earth, transforming an ancient ocean bottom into the world’s highest peak.