The First Three Minutes
Section 5 of 6
The Origin of the Elements
Part 4: The Origin of the Elements
Now the oldest thread in the course closes. We have watched the elements being made in three different cosmic foundries, across three modules:
- The first three minutes made the light nuclei: hydrogen, about a quarter helium, a trace of lithium. The raw material of everything.
- Stars (Module 3) fuse hydrogen and helium into carbon, oxygen, and on up to iron — the elements of rock, water, and life — over their long lives.
- Supernovae and neutron-star mergers (Module 4) forge and scatter the heaviest elements, the ones built by rapid neutron capture in the most violent deaths.

Quick check
A water molecule is . Where and when were its hydrogen and its oxygen made?
The hydrogen is primordial — made in Big Bang nucleosynthesis in the first three minutes, nearly as old as the universe. The oxygen was forged much later, by fusion inside a star and scattered when that star died. The two atoms in the same molecule were made about thirteen billion years apart, in entirely different cosmic environments.