Timeline of the Universe: 12 Eras from Big Bang to Stars

The universe is about 13.8 billion years old, and it splits neatly into 12 eras: the primordial universe, the particle era, nuclei and atoms, the first stars, galaxies and elements, the solar system, chemical origins, primitive life, complex life, human origins, civilization, and an interstellar era that has not happened yet. The first three eras fit inside the first 380,000 years. The solar system appears only 4.8 billion years ago, and the whole human story sits in the last 6 million years. Squeeze 13.8 billion years into one calendar year and all of civilization takes up the last 30 seconds of New Year's Eve.

The 12 eras at a glance

The cosmic calendar compresses the universe's history into one year. January 1 at 0:00 is the Big Bang and midnight on December 31 is today. The conversion is simple: calendar date = one year × (1 − years ago ÷ 13.8 billion). The dates below use 13.8 billion years (the Planck satellite's 2018 result is 13.787 ± 0.020 billion years).

To convert any year yourself, use the cosmic calendar calculator.

1. Primordial universe: the first instant

The primordial universe covers the first 10⁻³² seconds or so: the Planck epoch, the separation of gravity, grand unification, inflation and reheating. During inflation space stretched by a factor of about 10²⁶. Then the inflaton field decayed, its vacuum energy turned into particles and radiation, and a hot universe began.

The closer you get to the start, the more the picture rests on theory rather than direct observation. Inflation is the leading framework, not a settled fact.

2. Particle era: quarks, protons and neutrons

The particle era starts around 10⁻¹² seconds and ends a few tens of seconds in. Quarks move freely in a hot soup, get confined into protons and neutrons at about 10⁻⁶ seconds, neutrinos decouple at about 1 second, and electrons and positrons annihilate at about 10 seconds.

Matter survived because for every billion particle–antiparticle pairs there was one extra matter particle. Why is still an open question.

3. Nuclei and atoms: light elements and the first light

The nuclei and atoms era begins at 3 minutes, when about 25% of the mass turned into helium, with traces of deuterium and lithium. Alpher, Bethe and Gamow worked this out in Physical Review in 1948, the famous "αβγ paper".

About 380,000 years later electrons were captured by nuclei and the universe turned transparent. That light is the cosmic microwave background. Arno Penzias and Robert Wilson found it by accident at Bell Labs in 1965 while trying to get rid of antenna noise, and won the 1978 Nobel Prize in Physics. COBE measured its near-perfect blackbody spectrum in 1990 and found temperature ripples of one part in 100,000 in 1992, the seeds of galaxies.

On the calendar this whole era fits between Jan 1 and Jan 4. Recombination at 380,000 years lands at 0:14 on New Year's morning. After it come the dark ages: no stars, only neutral hydrogen slowly cooling.

4. First stars: the dark ages end

About 150 million years after the Big Bang, around Jan 4 on the calendar, the first stars lit up. Gravity gathered gas into dark matter halos, and the stars that formed may have been hundreds of times the Sun's mass. Their light re-ionized the hydrogen, the first supernovae scattered heavy elements, the first black holes formed, and quasars shone by about 700 million years.

Exact dates are uncertain. In 2024 the James Webb Space Telescope confirmed a galaxy, JADES-GS-z14-0, at redshift 14.32 (Carniani et al., Nature, 2024), about 290 million years after the Big Bang. That is earlier than older models expected.

5. Galaxies and elements: stars as forges

From about 1 billion years after the Big Bang (12.8 billion years ago, Jan 27), the galaxies and elements era begins. Galaxies grew through collisions, and the Milky Way is a barred spiral.

Stars forge the elements: three helium nuclei fuse into carbon, carbon burning makes oxygen, fusion stops at iron, and gold, platinum and uranium come from neutron star mergers. The element forges page shows where each one comes from.

6. Solar system: our corner

The solar system starts forming about 9 billion years after the Big Bang, roughly 4.8 billion years ago (Aug 27). The oldest solids in the solar system are 4.567 billion years old (Connelly et al., Science, 2012); the Sun ignited around then, on Sep 2 of the calendar. Jupiter grew fast, and about 4.5 billion years ago a body called Theia hit the young Earth and its debris became the Moon. The Late Heavy Bombardment around 4.1 billion years ago brought water, and by 4 billion years ago the surface had cooled enough for rain to fill the first oceans.

7. Chemical origins: raw materials for life

Between 4 and 3.8 billion years ago, chemical origins assembles the raw materials: amino acids, nucleotides, lipid membranes, the RNA world, self-copying molecules and finally protocells. In 1953 Stanley Miller made amino acids with an electric-spark experiment simulating early Earth, the starting point of the field.

How life began is still an open question, and each step is a candidate explanation. On the calendar this is around Sep 17.

8. Primitive life: 3 billion years of microbes

Primitive life begins about 3.8 billion years ago (Sep 22). The last common ancestor of all living things, LUCA, lived around 3.7 billion years ago. Bacteria and archaea split by 3.5 billion years ago, and microbial mats left stromatolite fossils.

Cyanobacteria began oxygenic photosynthesis about 3 billion years ago. The Great Oxidation Event around 2.4 billion years ago, on Oct 29 of the calendar, put oxygen in the air and killed off many anaerobes. Mitochondria arrived through endosymbiosis about 2 billion years ago, and cells with nuclei about 1.8 billion years ago. For most of this era, life stayed single-celled.

9. Complex life: from multicellular to dinosaurs

Complex life starts about 640 million years ago (Dec 15) with multicellular organisms. In the Cambrian explosion about 540 million years ago (Dec 17), eyes, shells and predators appear. Plants reach land about 470 million years ago and tetrapods about 370 million years ago.

The Permian extinction about 250 million years ago wiped out some 96% of marine species (Dec 25). An asteroid impact about 66 million years ago ended the age of dinosaurs (Alvarez et al., Science, 1980; Dec 30). The mass extinctions page covers each of the big five.

10. Human origins: the last few hours

Walking upright begins about 6 million years ago, which is around 20:11 on Dec 31, and starts the human origins era. The oldest well-dated stone tools are about 3.3 million years old (Harmand et al., Nature, 2015, Lomekwi, Kenya), and fire use goes back about a million years. Fossils from Jebel Irhoud in Morocco put the earliest Homo sapiens at about 300,000 years ago (Hublin et al., Nature, 2017), at 23:48. Humans spread out of Africa about 70,000 years ago and painted caves by about 40,000 years ago. For more on the different species, see the hominins page.

11. Civilization: the last 30 seconds

Farming begins about 12,000 years ago, which is 23:59:32 on the calendar, and starts the civilization era. Writing follows about 5,200 years ago (23:59:48), then bronze, iron, paper and printing. The scientific revolution is around 1600, the industrial revolution around 1760, and the first computers in 1946.

In 1969 Apollo 11 landed humans on the Moon. Carl Sagan proposed the cosmic calendar in The Dragons of Eden (1977).

12. Interstellar civilization: not yet

The interstellar civilization era is the only one of the twelve that has not happened. What has really happened is the 1969 Moon landing and Voyager 1 entering interstellar space in 2012 (Stone et al., Science, 2013). Mars bases, starships and Dyson spheres are still ideas.

Walk the timeline in a game

Cosmos Era is a hard sci-fi idle game that follows these same eras. In the game you start from a singularity and click your way up to interstellar civilization, unlocking different resources in each era. Game lore is labeled separately from real science, and the interstellar part is all marked as game lore. The full knowledge tree is on the cosmos tree page.

FAQ

How many eras are in the timeline of the universe?

There is no single standard. This article uses the 12 eras of the Cosmos Era encyclopedia: primordial universe, particle era, nuclei and atoms, first stars, galaxies and elements, solar system, chemical origins, primitive life, complex life, human origins, civilization and interstellar civilization. The last one has not happened.

When was the particle era?

From about 10⁻¹² seconds to a few tens of seconds after the Big Bang. Quarks were confined into protons and neutrons, and most electrons and positrons annihilated. On the cosmic calendar it does not get past Jan 1, 0:00.

When do humans appear on the cosmic calendar?

Using 13.8 billion years, human ancestors from 6 million years ago appear around 20:11 on Dec 31, modern Homo sapiens (300,000 years ago) at 23:48, and farming and civilization in the last 30 seconds.

How do we know the universe is 13.8 billion years old?

Mainly from measurements of the cosmic microwave background. The Planck satellite's 2018 result is 13.787 ± 0.020 billion years, usually rounded to 13.8.

Where does the solar system fall on the cosmic calendar?

The solar system starts forming around Aug 27, the Sun ignites around Sep 2, and the earliest life on Earth shows up in late September. Sagan used an older, larger age in 1977, so his dates differ slightly.

Next steps

To try it yourself, play the game. To convert any other year, use the cosmic calendar calculator.