There is the possibility that strange matter was formed early in the evolution of the Universe. While such a scenario requires some fairly lucky coincidences, it produces some interesting results and in any case cannot be ruled out.
Witten's model of this process begins with the assumption of a first order phase transition in the early Universe from a high temperature state of quasi-free light quarks to a state of hadronic matter. Low temperature bubbles of hadronic matter will form as the Universe expands, then grow as they absorb energy from their surroundings. At some point the lower energy `bubbles' will percolate, and soon after it is the high energy regions that form bubbles. As the Universe continues to expand, the high energy free quark bubbles continue to give off energy.
This release of energy may take two forms. If it comes from evaporation, i.e. the release of hadrons into the low temperature region, then the bubbles will continue to shrink until they disappear. If instead they loose energy via neutrino emission, the baryon number inside the bubble will remain constant while energy is released. The bubbles will continue to shrink in size, increasing the baryon density. Eventually the excess baryons inside will produce a pressure to resist further contraction.
These lumps now contain between 80% and 99% of all the baryon excess in the Universe, but are only about 1 cm in radius. The density of these lumps of hot quark matter would be about g/cm . They would not have been incorporated into stars or or planets. In order for these lumps to survive, they could not be composed of normal matter, but instead would be composed of quark matter. From the models of bulk matter it is clear that this would be strange quark matter. The large mass contained in these objects makes them a good candidate for dark matter, and in fact they have certain properties consistent with many particle physics explanations of dark matter. This comes with the important caveat that it requires some conspiracy in many QCD parameters. It also assumes that the loss of energy from the hot bubbles proceeds primarily via neutrino emission and not evaporation, which is highly suspect.