"And cells, in turn, are made of molecules and molecules are made of atoms. Dig even deeper and pretty soon you’ll find yourself at the level of electrons and quarks. These are the particles that have traditionally been considered to be the end of the line, the fundamental building blocks of matter."

To me, the so-called "the end of the line" is a philosophical question not a physics question. For the simple reason that, we can never know, if something is really indivisible, or if we are unable to divide it because of our insufficient technology. We can never know this. The story of physics makes this clear. Each generation of physicists with new techology available to them take pride in showing that the previous generetion was lying, and that it is their atoms which are the real "end of the road". Then comes the next generation with a better technology...