A faint glow fills the entire universe – the “afterglow” of the Big Bang. The glow was created when the first atoms formed – 380,000 years after the Big Bang. But the glow isn’t smooth – it has tiny ripples and bumps. That’s because the universe itself wasn’t smooth – there were slight differences in the density of matter. Without those differences, we wouldn’t exist.

The denser regions had a slightly stronger gravitational pull, so they drew in the material to make the first stars and galaxies.

The first stars were born in as little as a hundred million years. They were made almost entirely of hydrogen and helium, which were created in the Big Bang.

The stars probably were quite heavy, so they burned out in a hurry. They forged heavier elements in their cores, then blasted them into space when they died. Some of those elements were incorporated into later generations of stars. Those stars created more heavy elements and flung them into space as well, and so on. The heavier elements are the ingredients for planets and everything on them – including us.

Galaxies began to form about four hundred million years after the Big Bang, as stars and gas clouds clumped together. More stars and galaxies are being born today, but not as many. In fact, most of the stars and galaxies that will ever be born have already taken shape. So the universe may face a cold, dark fate, and we’ll talk about that tomorrow.

Script by Damond Benningfield