surface of Mars -- nearly two and a half times the height of Mount Everest. On Earth, you

would need a spacesuit to survive at that altitude - but could there even be a mountain

that tall here on our home planet?

Based on the strength of Earth's gravity and the density and strength of rock, in principle

you could make a single conical mountain that stretched between New York and Chicago and

soared over 45km! That's twice the size of Olympus Mons and definitely dwarfs Everest.

However, there are a couple of reasons why we can't actually have that humongous of a

mountain on Earth:

For one, Earth's crust is made up of continental plates that essentially float in the semi-solid

rock of the mantle below. If you add more weight above the surface, they sink lower

into the earth's hot interior, and when they sink far enough, they soften and basically

melt. For our conical mountain, that gives a new height limit of just 15km.

As well, the powerful collision of two tectonic plates, which creates mountains in the first

place, also fractures and cracks the rock, weakening its structure and exposing it to

erosion.

Over millions of years, freeze-thaw cycles pry at these cracks, while winds claw at the

slopes and streams and glaciers carve deep valleys into the mountainside, all weakening

the mountain's support. This can end badly.

For example, 3,764m tall Aoraki/Mount Cook in New Zealand had its top fall off one night

in 1991, trimming it down to a 3,754m mountain.

Given all the factors that conspire to limit the height of mountains - sinking into the

earth's mantle, fractures, and erosion - I wouldn't bet on our tallest mountains getting

too much taller than they already are. Then again, Mount Everest is still growing, 50

years from now, it could be 30 cm taller than it is today... or it could be a good deal

shorter. We'll just have to wait around to find out. And, who knows? Maybe we'll be on

Mars by then, anyway.