Where Elements Come From
Explain stellar nucleosynthesis: the Big Bang produced mainly hydrogen and helium; main-sequence fusion builds elements up to iron; and supernovae produce elements heavier than iron and scatter them into space — meaning the atoms in our bodies were forged in ancient stars
What a learner can do afterwards
- States that the Big Bang produced primarily hydrogen and helium, and that all heavier elements were made later in stars
- Explains that nuclear fusion in main-sequence stars converts hydrogen to helium and can continue building heavier elements up to iron
- Explains why elements heavier than iron require supernova explosions to form, and describes how supernovae distribute these elements into interstellar space where they become the raw material for new stars, planets, and life
The lesson
Right after the Big Bang, the universe held almost nothing but hydrogen and helium, the two lightest elements. Every heavier element you know, carbon, oxygen, iron, had to be built somewhere else, much later.
Stars are element factories. In a main-sequence star, gravity crushes the core until hydrogen nuclei fuse into helium. As the star ages, it keeps fusing heavier nuclei together, helium into carbon, carbon into oxygen, and so on, all the way up to iron.
Fusing iron actually costs more energy than it releases, so a star cannot power itself that way. Iron piles up in the core until the star collapses and explodes as a supernova. That explosion is violent enough to fuse iron into even heavier elements, like gold and uranium, and it blasts every element the star ever made out into space.
The gas a supernova scatters becomes the raw material for new stars, new planets, and eventually new life. The calcium in your bones and the iron in your blood were forged inside a star that exploded long before the Sun existed.
Hydrogen and helium came from the Big Bang, stars fused them into heavier elements up to iron, and supernovae made everything heavier and scattered it into space, including the atoms now inside you.
Watch it
Where it sits
This opens up
Nothing builds on it yet.
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.