EPOCH OF RECOMBINATION

Immediately after the Big Bang, the Universe was extremely hot and dense. Under these conditions, atoms could not exist, and the matter was distributed as a highly ionised plasma. As the Universe expanded however, its density and temperature dropped until after about 380,000 years the conditions were such that ions and electrons could 'recombine' to form atoms ( mostly hydrogen and helium). This is known as the 'epoch of recombination'.