Older Than Earth

Chapter I · The beginning

The first three minutes §

The universe is 13.787 billion years old, give or take 20 million.

• 13.787billion years, ± 20 million
• 5%of everything is atoms
• 200 Myruntil the first stars

About 75% of ordinary matter stayed hydrogen, and about 25% became helium. A pinch of lithium seasoned the mix. Everything heavier — every atom of carbon in you, every atom of oxygen — came later, and this page follows each of them home.

Your atoms are the 5%: ordinary matter is less than one twentieth of everything there is. The rest is dark matter and dark energy, and neither ever became you.

1. 0–1 sNeutrons and protons freeze out at one to six.
2. ~100 sDeuterium survives; helium assembly begins.
3. ~3 minOne quarter of all mass is helium now.
4. ~200 MyrDarkness ends; the first stars switch on.

The first stars switched on about 200 million years after the Big Bang.

Chapter II · First light

The quiet forges §

The first stars were furnaces with no metal in them — hydrogen, helium, a whisper of lithium. In their cores, and in the red giants that followed, three helium nuclei learned to stick together as carbon.

That step should barely happen. It works only because carbon has a resonance at exactly the right energy — and Fred Hoyle told the Caltech lab it had to be there before they found it.

In 1957 four physicists — Margaret Burbidge first among them, with Geoffrey Burbidge, William Fowler, and Fred Hoyle — showed how stars forge the elements. Their paper still underlies every origin story on this page, including yours.

Most of the carbon and nitrogen in you — the backbone of your DNA — breathed out of aging stars like these, on slow winds, billions of years before the Sun existed.

Chapter III · Cataclysms

The violent forges §

Your oxygen was forged in massive stars and freed when they exploded.

Massive stars live fast — millions of years, not billions — and die as supernovae, fusing oxygen, sodium, magnesium, phosphorus, sulfur, chlorine, potassium, and calcium in their final burning and their blast.

Your iron was forged in both kinds of supernovae. Collapsing massive stars make it, and so do exploding white dwarfs — the embers of quiet stars, reignited.

Chapter IV · Collisions

When dead stars collide §

On 17 August 2017, detectors on Earth heard two neutron stars spiral into each other in the galaxy NGC 4993 — and telescopes watched the gold being made.

It was the first concrete proof that such smashups are the birthplace of half of the elements heavier than iron, including gold and platinum — the observing team's own words.

One collision forged about 10,000 Earth-masses of heavy elements.

That same merger made some ten Earth-masses of gold and platinum. Your gold was most likely forged the same way: in a flash like that one, billions of years before the Sun.

Chapter V · Assembly

You, assembled §

About 63 of every 100 atoms in you are hydrogen. Most of it is primordial: born in the first minutes, before the first stars existed.

A 70-kilogram body holds about 7 octillion atoms. That number is computed on this page from the reference table in the previous chapter — and the calculator below runs it for your own weight.

• Oxygen65%
• Carbon18%
• Hydrogen10%
• Nitrogen2.6%
• Calcium1.3%
• Phosphorus0.6%
• Everything else2.5%

Bars under 1% are drawn at a 3 px floor; the labels carry the exact values.

Earth is 4.54 billion years old, and life has left traces for at least 3.48 billion of them. The solar system itself condensed 4.567 billion years ago — so nearly every atom in you is older than the Sun.

The nitrogen in our DNA, the calcium in our teeth, the iron in our blood, the carbon in our apple pies were made in the interiors of collapsing stars. We are made of starstuff.

Summary

In short §

Are we made of stardust?

Partly: about 37 of every 100 atoms were forged in stars; about 63 are primordial hydrogen, older than the stars.

How many atoms are in the human body?

About 7 octillion in a 70-kilogram adult — run your own weight through the calculator above.

Where does gold come from?

Most likely from colliding neutron stars: one 2017 merger made some ten Earth-masses of gold and platinum.

How old is the universe?

13.787 billion years, give or take 20 million.

What is the oldest thing in me?

Your hydrogen: most of it is 13.8 billion years old.

Lookup

Find your element §

Element name Find it

Pick a name to see where it was forged.

• H
• He
• Li
• C
• N
• O
• Na
• Mg
• P
• S
• Cl
• K
• Ca
• Fe
• I
• Au

Cinema

Play the universe §

Check yourself

Five questions §

Score: 0/5

1. Chapter I

   What did ordinary matter become in the first minutes?

   About 75% became helium and 25% stayed hydrogen75% of ordinary matter stayed hydrogenAbout half became carbon and half stayed hydrogenAbout 99% became iron within the first hour

2. Chapter II

   How old is the nearby star HD 140283 dated?

   14.46 billion years old4.46 billion years, younger than the Earth14.46 million years, practically newborn140 billion years, ten times the universe

3. Chapter III

   Where was your oxygen forged?

   in the Big Bang's first minutesin merging neutron starsforged in massive starsin the Earth's core

4. Chapter IV

   How much heavy-element matter did the 2017 neutron-star merger forge?

   about 10 Earth-massesabout 10,000 Earth-masses of heavy elementsabout 10,000 Sun-massesno heavy elements at all

5. Chapter V

   How many of every 100 atoms in you are hydrogen?

   26 of every 1009 of every 10097 of every 10063 of every 100

Share my score

Evidence

Sources and method §

Every number on this page comes from a published source or a calculation shown beside it. Amounts in you assume a 70-kilogram reference adult with average composition; real bodies vary.

The universe

• Planck Collaboration 2020 — the age, 13.787 ± 0.020 billion years. Paper VI, cosmological parameters
• NASA / Planck — ordinary matter 4.9%, dark matter 26.8%, dark energy 68.3%. Content of the universe
• E. Wright, UCLA — Big Bang nucleosynthesis: 25% of mass into helium, in the first minutes. Tutorial
• NASA StarChild / WMAP — the first stars, about 200 million years in. When did the first stars form?

The stars

• Burbidge, Burbidge, Fowler & Hoyle 1957 — elements forged in stars. About the B2FH paper
• Hoyle 1953/54, Dunbar et al. 1953 — carbon's 7.68 MeV resonance, predicted then found. Triple-alpha review
• Bond et al. 2013 — HD 140283 at 14.46 ± 0.80 billion years. Nearby ancient star
• NASA Hubble 2013 — that star sits 190.1 light-years away, in Libra. Birth certificate of the oldest known star
• Johnson 2019, Science 363, 474–478 — the six origin channels behind the table.

You

• Body-composition table (after Emsley 2011) — mass fractions and the 70 kg reference. Composition of the human body
• StatPearls / NCBI — about 60% of an adult is water. Insensible fluid loss
• NIH Office of Dietary Supplements — 3 to 4 grams of iron, most in hemoglobin. Iron fact sheet
• Connelly et al. 2012, Science — the solar system at 4567.30 million years. Absolute chronology
• Patterson 1956 — Earth at 4.54 billion years, from lead in meteorites. How the age is measured
• Djokic et al. 2017, Nature Communications — life's traces back 3.48 billion years. Earliest signs of life on land

The collision

• Kasliwal et al., Science 2017 — the GW170817 kilonova paper. doi:10.1126/science.aap9455
• Caltech GROWTH team 2017 — first proof of the merger forge; 10,000 Earth-masses. Strike gold
• E. Berger (Harvard/CfA) 2017 — some ten Earth-masses of gold and platinum. First neutron-star merger seen
• Estimates vary: up to ~100 Earth-masses of gold in some models. Gravitational-wave astronomers hit mother lode

The words

• Carl Sagan, Cosmos episode 1 (1980), as transcribed.