From Big Bang to AtomsEdit
Big Bang, a great explosion that happened around 13.75 ± 0.11  billion years ago , is thought to create our universe. The idea is based on the observation that our universe is expanding, so it was probably a single point at some time in the past if we trace back.
At about 10-6 seconds after the explosion, quarks and gluons combined to form baryons such as protons and neutrons, while anti-quarks and anti-gluons formed anti-protons and anti-neutrons. A small excess of quarks and gluons over theri anti-particles led to a small excess of baryons over anti-baryons. Latter, the universe cooled to a level that it could not produce gluons, quarks, anti-gluons and anti-quarks. This led to a dramatic decrease in the universe mass: matter and anti-matter 'eats' each other, left only 1 of 1010 protons and neutrons survive and none of their anti-particles. That's why the universe now is a matter environment, not an anti-matter one :)
At one second after the explosion, same thing happened to electrons and positrons (positrons are anti-electrons)
A few minutes after the explosion, the temperature was about 109 K. The energy was still so high. Protons and neutrons didn't combine yet. When the universe got cooler, the strong force (a powerful but short-range force) got advantage, combined protons and neutrons together, formed nuclei. After 379,000 years, electromagnetic force (a weak but long-range force) got advantage, making electrons first attached to nuclei. The first atom was born, consisting of a nuclei (protons, neutrons) and one or more electrons.
- , Seven-Year Wilkinson Microwave Anisotropy Probe (WMAP1) Observations: Sky Maps, Systematic Errors, and Basic Results, page39.