The Big Bang occurs and about 5 microseconds later there is a phase transition in the cosmological evolution. As the energy density falls in the course of expansive cooling, the "critical" energy density of Quantum Chromodynamics (QCD) is reached, at about 1GeV per cubic Fermi, at which free quarks and thermal gluons neutralize their strong-interaction "colour" fields, in binding to composite "quark atoms": our familiar protons and neutrons. This so-called colour confinement phase transition is the consequence of the self-energy of an isolated colour charge (as carried by quarks and gluons), which diverges at falling density, getting infinite in vacuum. The bound state creation is, thus, not the result of mutual attractive binding forces, but of a confining, repulsive vacuum. The familiar protons/neutrons thus receive their mass, not from an approximate sum of their (quark) constituent masses--as is the case in all other known bound states--but predominantly from trapped vacuum energy density prevailing at confinement time. This is the first composite structure in the universe: remarkably unfamiliar! However, the confinement transition between quarks and protons has recently become accessible to laboratory experiments, in collisions of relativistic nuclear projectiles which re-create primordial cosmic evolution energy densities.