Where did the elements that make up our bodies come from?
Unraveling 13.8 billion years of cosmic history
About 13.8 billion years ago, the universe began as a "Big Bang" — an extremely hot and dense fireball.
"Big Bang"
Birth of the universe. Temperature exceeds 10^32 degrees
Formation of Protons and Neutrons
Temperature drops to 10 billion degrees, quarks combine
Start of Nucleosynthesis
Nuclei of hydrogen, helium, and lithium are created
Recombination Era
Electrons bind to nuclei, light can travel freely
75%
Hydrogen (H)
Most abundant element in the universe
24%
Helium (He)
Second most abundant element
<1%
Lithium (Li)
Produced in trace amounts
Key Point: Only light elements (H, He, Li) were created in the Big Bang. Heavier elements were born elsewhere.
A few hundred million years after the Big Bang, hydrogen gas accumulated and "the first stars" were born. In the cores of stars, nuclear fusion reactions continuously create new elements.
4H → He + Energy
Main reaction in main-sequence stars (like the Sun)
3He → C, C + He → O
Occurs in red giants. Produces carbon and oxygen
C + C → Ne, Na, Mg
Occurs in massive star cores
Si + ... → Fe
Final stage. Reaction stops at iron
The Iron Wall: Elements heavier than iron cannot be created by normal nuclear fusion. Iron has the most stable nucleus.
When a massive star reaches the end of its life, a spectacular event called a supernova explosion occurs. In this explosion, elements heavier than iron are created rapidly.
Massive stars (8+ solar masses) undergo gravitational collapse and explode
Elements produced: Fe, Ni, Co, Zn, Cu, etc.
White dwarf absorbs matter from companion star and explodes
Elements produced: Fe, Ni, Si, S, etc.
Scattered as Stardust: Heavy elements created in supernovae are scattered into space, becoming material for the next generation of stars and planets. Earth and our bodies are composed of elements born from these "stellar deaths."
To create elements heavier than iron, a special process called neutron capture is required.
Slow neutron capture inside red giants. Has time for β-decay, so many stable isotopes are formed.
Elements produced:
Sr, Y, Zr, Ba, Pb, etc.
Instantaneous capture of many neutrons during supernovae or neutron star mergers. Creates heavy elements rapidly.
Elements produced:
Au, Pt, U, Th, Eu, etc.
In 2017, humanity made a historic discovery. The observation of a neutron star merger revealed where precious metals like gold and platinum are created.
Observed on August 17, 2017
First multi-messenger astronomy observation in human history
16,000
16,000× brighter than a nova
10 Earths
Amount of gold produced
130M ly
Distance from Earth
The Origin of Gold Jewelry: The gold jewelry you wear is made of atoms created billions of years ago when neutron stars collided.
Elements born from 13.8 billion years of cosmic history. Which element is most like you?
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