Cosmologists have pegged the time of first attraction between helium nuclei and electrons at about 15,000 years after the Big Bang, with the second electrons needed to complete the atom being brought at around the 100,000 year mark.
HOW???
@phoghat: I'm not even remotely an expert, but I'd guess they arrive at that figure through their estimations of the size and temperature of the universe at that given point combined with the electrical charge of the helium nuclei. 15,000 years is probably around when the universe was cool and big enough for the helium nuclei to attract electrons without interference from photons. However, once that first electron was in place, the charge of the now unstable atom was considerably less, meaning it took a while longer for the universe to get big and cool enough for the second electron to be attracted.
Again, not an expert, and I could be very, very wrong.
08/23/09
I'm sure John Carter and Dejah Thoris will look favorably upon their quest.
08/23/09
...just kidding..
08/22/09
HOW???
08/22/09
Again, not an expert, and I could be very, very wrong.