I don't want to give the impression that we aren't pretty sure the first generation of stars were just hydrogen and helium. As shown here, primordial clouds have been found that are just hydrogen and helium, no higher elements. (It also discusses in detail the difficulty of trying to catch glimpses of that earliest generation of stars.) We'll probably see a lot more when the next generation of infrared space telescopes are launched around 2018.
The universe starts to become less opaque relatively early, about when it's 380,000 years old, but doesn't get to less than 10% opaque till it's about a billion years old. So it's a gradual thing. The important thing is that supernovas are essentially to spreading the elements that are "cooked" in stars out to the rest of the universe. Annnnd that's essential to Coincidence Two.
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