The C in E = MC²

Ever since high school I've wondered what the speed of light has to do with Einstein's formula

Solving the equation for C, you get

Take Energy, divide by Mass, and the square root of the result is the speed of light. How can that be?

I just realized (at age 71) that the answer is in a web page I put up a couple of years ago - Why a Rock is Heavy.

It is well known from Einstein's Relativity that when a particle with mass moves faster and faster, it's mass increases. The quarks that make up protons and neutrons in an atomic nucleus are moving at nearly the speed of light.

98.5% of the weight of matter is from the energy of motion of the quarks inside protons and neutrons.

This says that most mass is CAUSED by quarks moving near the speed of light (through the Higgs Field). The speed of light has EVERYTHING to do with E = MC².