Mount Everest isn't the Earth's tallest mountain
Mount Everest is the tallest mountain above sea level, but if we're talking sheer height here, base to summit, then the tallest mountain is Mauna Kea on the Island of Hawaii.
Here's how it breaks down:
Everest stands 29,035 feet above sea level. Mauna Kea only stands 13,796 feet above seal level, but the mountain extends about 19,700 feet below the Pacific Ocean. Over half of it is submerged.
That puts the total height of Mauna Kea at about 33,500 feet - nearly a mile taller than Everest.
Mauna Kea is actually an inactive volcano on the big island of Hawaii. It is about a million years old, created when the Pacific tectonic plate moved over the Hawaiian hotspot - a plume of liquid magma from deep inside Earth. It last erupted about 4,600 years ago.
You can tell just how giant Mauna Kea really is in the graphic below:
The summit is an astronomer's paradise: it has low humidity, clear skies, and lots of distance from any light pollution.It offers what's arguably the best view of the observable universe, and right now the summit is host to 13 telescopes.
Construction of a 14th telescope recently inspired mass protests on the mountainside by native Hawaiians who consider Mauna Kea sacred ground. The controversy has split the astronomy community in two and brought the construction of the telescope to a grinding halt. It's unclear when the building will resume.
If you climb Mauna Kea, then you'll have technically scaled the tallest mountain on Earth. You just majorly cheated by starting more than half way up the mountain.