How was Mount Everest formed? A mountain made by colliding plates

Mount Everest was formed by a collision between continents. India, once an island continent far to the south, drifted north on its tectonic plate and ran into Asia about 50 million years ago. Neither landmass could sink, so the crust between them crumpled, stacked and rose into the Himalayas. The rock at Everest's summit is limestone that formed on a seafloor about 450 million years ago, which is why it holds the remains of sea creatures, 8,849 m up.

In short

• Everest is made of old ocean-floor and continental rock that the India–Asia collision pushed up and stacked in slabs, not of volcanic rock.
• Its official height, 8,848.86 m, comes from a joint China–Nepal survey announced on 8 December 2020; earlier figures differ because of methods and snow.
• It still rises a few millimeters a year as India keeps pushing north, while erosion and gravity wear it down.

How did India's collision with Asia build the Himalayas?

The story starts with the breakup of Pangaea. India was then part of the southern supercontinent, Gondwana, beside Africa, Antarctica and Australia, and an ocean, the Tethys, lay between it and Asia. As the note on plate tectonics explains, ocean floor can sink under a continent but continents themselves are too light to sink.

The steps, with dates from the U.S. Geological Survey's account of the Himalayas:

When	What happened
About 450 million years ago	Limestone forms on a shallow seafloor from the shells and skeletons of sea animals; this rock will become Everest's summit
About 200 million years ago	Pangaea breaks apart, and India begins moving north
About 80 million years ago	India is about 6,400 km south of Asia, moving north at about 9 m a century, fast for a plate
About 50 to 40 million years ago	The Tethys ocean floor has sunk beneath Asia, and India hits Asia; its advance slows by about half
The last 10 million years	Most of the Himalayas' and Tibet's height is built
Today	India is still moving north into Asia at a few centimeters a year

When the two continents met, the edge of India was driven under Asia and the rock between them was sliced into great slabs that were pushed over one another along low-angle faults, like a rug rucked up against a wall. The crust under the Himalayas and Tibet is now about twice its normal thickness, roughly 70 km, and that thick, light root is what holds the mountains up, the way a thick block of wood floats higher in water than a thin one. The same squeeze lifted the Tibetan Plateau to an average of more than 4,500 m.

Everest is not a volcano. There is no subduction of ocean floor at the Himalayas today, so no volcanoes form there; the mountains are pushed-up rock, not erupted rock.

Why are there sea fossils on top of Everest?

The summit is made of the Qomolangma Formation, an Ordovician limestone that runs from the top down to about 8,600 m. Limestone forms in the sea, and samples from near the summit contain fragments of trilobites, crinoids (relatives of sea stars) and tiny shelled crustaceans called ostracods, according to geologists' analyses summarized on Wikipedia. Below it is a band of yellowish marble, the Yellow Band that climbers cross, and below that older, more strongly heated rock.

How the seafloor got up there, in three steps:

1. The limestone formed on the floor of a shallow sea, at roughly sea level or a little below, about 450 million years ago.
2. It lay on the northern edge of India's continent, where the Tethys Sea met the land, and was buried under later sediment for hundreds of millions of years.
3. The collision lifted it to 8,849 m. Over about 50 million years, that is an average of 8,849 m ÷ 50,000,000 years, about 0.18 mm a year.

The real uplift was faster than that average, because erosion removed a great deal of rock as it rose, and most of the height came late. But the arithmetic makes a point: a fraction of a millimeter a year, kept up for tens of millions of years, is enough to put a seabed at the top of the world.

Why do different sources give different heights?

Everest's height depends on what is measured and how. The main surveys:

Year	Who measured	Height	Measured
1856	Great Trigonometrical Survey of British India	29,002 ft, about 8,840 m	Snow top, from stations in the plains up to 240 km away
1952–54	Survey of India	8,847.73 m, rounded to 8,848 m	Snow top, by triangulation
1999	American expedition led by Bradford Washburn	8,850 m	Rock, using GPS on the summit
2005	Chinese Academy of Sciences and State Bureau of Surveying and Mapping	8,844.43 m	Rock, beneath about 3.5 m of snow and ice
2020	Nepal and China, jointly	8,848.86 m	Snow top, by GPS and China's BeiDou system, with gravity measurements

Three things explain the differences. First, whether the survey measures the rock or the snow and ice on top of it, which differ by several meters. Second, what "sea level" means under a mountain thousands of kilometers from any sea: surveyors use the geoid, an imagined sea surface shaped by Earth's gravity, and better gravity measurements shift the answer. Third, the mountain itself moves: Nepal's 2019 survey was partly to check whether the April 2015 Gorkha earthquake had changed its height. The 2020 figure, 8,848.86 m, is the snow-top height both countries agreed to use.

Is Mount Everest still growing?

Yes, slowly. India is still pressing into Asia, and GPS stations on the mountain show its summit moving northeast by a few millimeters to a few centimeters a year and rising by a few millimeters a year. Published rates differ; a figure often cited is about 2 mm a year upward, and the 2024 study described below puts the part added by river erosion at about 0.16 to 0.53 mm a year.

A few millimeters doesn't mean Everest will tower over everything in a few million years. Take 2 mm a year:

1. In a human lifetime of 80 years: 80 × 2 mm = 16 cm.
2. In 10,000 years: 20 m.
3. In 1 million years: 2,000 m, which would make it nearly 11 km high.

That doesn't happen, because uplift isn't the only process. Glaciers, rivers and landslides strip rock off the Himalayas, and very high mountains are weighed down by their own mass, so the crust spreads and sinks. Earthquakes can lower parts of the range as well as raise them. Over long times, uplift and wearing-down roughly balance, so the Himalayas stay near their height while their rocks are constantly replaced.

Still argued

Why Everest stands about 250 m higher than its neighbors is debated. A 2024 study in Nature Geoscience by Han and colleagues proposed that about 89,000 years ago the Arun River captured another river system and began cutting a deep gorge near Everest. Removing that much rock lightened the crust, which rebounded upward, and the authors suggest this explains about 15 to 50 m of Everest's extra height and part of its recent uplift rate. A formal comment challenging the study, a Matters Arising, was published in the same journal on 31 July 2026. The idea is plausible physics; how much it explains is unsettled.

Is Everest really the tallest mountain on Earth?

It is the highest above sea level, but "tallest" can be measured three ways, and each gives a different winner, according to NOAA's National Ocean Service.

Measure	Winner	Figure	Why
Highest summit above sea level	Mount Everest, Nepal and China	8,848.86 m	The highest point of land above the sea's surface
Tallest from base to peak	Mauna Kea, Hawaii	More than 10,210 m, of which 4,207 m is above sea level	It starts on the deep floor of the Pacific
Summit farthest from Earth's center	Chimborazo, Ecuador	6,268 m above sea level, but more than 2,072 m farther from the center than Everest's summit	Earth bulges at the equator, and Chimborazo is one degree south of it

Mauna Kea is a volcano built by the Hawaiian hotspot, so it is a different kind of mountain altogether, as the note on how volcanoes form explains. And the deepest point of the ocean floor, the Challenger Deep, is so far down that Everest would fit inside the Mariana Trench with about 2 km of water above its top.

Check yourself

• Without looking back: why did India's collision with Asia build mountains instead of one continent sinking under the other?
• How did limestone full of sea creatures end up at 8,849 m?
• Why have surveys of Everest's height given different answers?

Sources

• The Himalayas: two continents collide, in This Dynamic Earth — U.S. Geological Survey
• Understanding plate motions, in This Dynamic Earth — U.S. Geological Survey
• What is the highest point on Earth as measured from Earth's center? — NOAA National Ocean Service
• Recent uplift of Chomolungma enhanced by river drainage piracy — Han and others, Nature Geoscience, 2024
• Mount Everest — Wikipedia