Is "Mount Everest is the tallest mountain on Earth" true?
Everest gets crowned tallest mountain on Earth in basically every geography unit, measured proudly from sea level to summit. That measurement is accurate as far as it goes; it's just not the only way to measure a mountain. Count how far a peak actually rises from its own base, ocean floor included, and Hawaii's Mauna Kea, mostly submerged, actually climbs even higher than Everest does. "Tallest" depends entirely on where you start counting from.
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What you were taught
Mount Everest is the tallest mountain on Earth
What we know now
Everest is the highest mountain above sea level, but Mauna Kea in Hawaii is taller when measured from its base on the ocean floor. The difference depends on how "tallest" is defined.
Was "Mount Everest is the tallest mountain on Earth" taught in school?
Yes — and not as a joke question on a quiz. This geography claim showed up in textbooks, worksheets, and classroom posters through the 1980s, which is why so many people still remember it as settled fact long after the science moved on.
Is "Mount Everest is the tallest mountain on Earth" true?
No. Everest is the highest mountain above sea level, but Mauna Kea in Hawaii is taller when measured from its base on the ocean floor. The difference depends on how "tallest" is defined. If you want the primary citation, start with USGS - How Do Mountains Form?
When was this understanding updated?
The evidence had largely shifted by around 1983. Schools don't flip overnight, though — plenty of classrooms kept teaching the older version for years after researchers had already moved on.