How stars build the elements

Science · Space Exploration · ages 12-14

Name ______________________ Date ____________

In a main-sequence star's core, hydrogen fusion produces which element?
- Carbon
- Helium
- Iron
Which two elements did the early universe mainly produce?
- Hydrogen and helium
- Carbon and oxygen nuclei
- Silicon and iron nuclei
Every element heavier than iron must be made in a supernova.
Circle one: True False
How can material ejected by a supernova become part of a new planet?
- It mixes into gas and dust that later form a planetary system
- It stays sealed inside the remnant and becomes a planet without leaving
- It changes entirely into light that later turns directly into a planet
Why can't fusing iron into heavier nuclei power a massive star?
- Iron nuclei cannot take part in any nuclear reaction
- Gravity disappears whenever iron reaches a star's centre
- It takes energy instead of releasing energy
A Sun-like star will build an iron-rich core during its later stages.
Circle one: True False
Order one possible history: (1) Big Bang, (2) a supernova ejects stellar material, (3) a massive star's later burning builds an iron-rich core, (4) a planet forms using some ejected material.
- 3, 1, 2, 4
- 1, 2, 3, 4
- 1, 3, 2, 4
A classmate says, 'Ordinary chemical reactions on Earth created the carbon nuclei in my body.' Which correction fits the lesson?
- Carbon nuclei cannot survive in living cells, so the body contains none of them
- Those nuclei formed in earlier stars, before the Solar System existed
- Volcanoes create new carbon nuclei whenever chemical reactions release carbon gas

Answer key

For grown-ups. Fold this page away before handing over the rest.

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Helium · Main-sequence core fusion converts hydrogen into helium and releases energy. Later nuclear-burning stages are different.
Hydrogen and helium · Early nuclear reactions produced mainly hydrogen and helium, with traces of lithium. Carbon, oxygen and iron formed later.
False · Neutron capture builds elements beyond iron in several settings, including aging stars and neutron-star mergers. A supernova is not required in every case.
It mixes into gas and dust that later form a planetary system · Ejected material can mix into clouds between stars. Some enriched clouds later form stars and planets.
It takes energy instead of releasing energy · A process that takes energy cannot supply the energy a star needs. This does not mean iron nuclei can never undergo nuclear changes.
False · A Sun-like star can produce carbon and oxygen through helium fusion, but does not build an iron core. Much more massive stars can reach later burning stages.
1, 3, 2, 4 · The Big Bang precedes stars. In this path, later stellar burning precedes the supernova, and the planet forms using material already ejected.
Those nuclei formed in earlier stars, before the Solar System existed · The carbon nuclei in your body formed in earlier stars. Ordinary chemical reactions rearrange atoms rather than create carbon nuclei.