Where the iron in a rock comes from
1 min 41 s. The words are spoken and shown in the picture; the player can also show them as subtitles.
For the Earth and Space Sciences Regents. Topic: Stellar nucleosynthesis in massive stars, with the past questions on it.
What Dr. Mars says (the words of the video)
Where does the iron in a rock come from?
Dr. Mars taps a rock rich in iron.
Iron's chemical symbol is F e.
Iron like this was made in stars before Earth formed.
Dr. Mars follows the iron back to a massive star.
Fusion joins the nuclei, or centers, of light atoms into heavier ones.
All stars, our Sun too, first fuse hydrogen into helium at the center.
A massive star continues: each stage makes a heavier element.
Each new stage forms a layer inside the one before.
In this star, each stage is shorter than the one before.
Hydrogen to helium: millions of years. Silicon to iron: one day.
The layers end at a core of iron, at the center.
Then the iron core collapses: it falls inward.
The star explodes and spreads its elements into space.
Earth later formed from gas and dust that held elements like these.
Check yourself! Which part of this star formed last: A, B, or C?
Think: where does each new stage form?
Answer: C! The iron core formed last, at the center.
Dr. Mars traced the iron in his rock back to a star like this.
Dr. Mars. Free practice for the New York Earth and Space Sciences Regents.