  Big-Bang nucleosynthesis (BBN) represents one of the earliest phenomena that
can lead to observational constraints on the early Universe properties. It is
well-known that many important mechanisms and phase transitions occurred before
BBN. We discuss the possibility of gaining insight into the primordial Universe
through studies of dark matter in cosmology, astroparticle physics and
colliders. For this purpose, we assume that dark matter is a thermal relic, and
show that combining collider searches with dark matter observables can lead to
strong constraints on the period of freeze-out before BBN.
