# Timeline of the universe

The timeline of the universe begins with the Big Bang, 13.799 ± 0.021 billion years ago, and follows the formation and subsequent evolution of the Universe up to the present day. Each era or age of the universe begins with an "epoch", a time of significant change. Times on this list are relative to the moment of the Big Bang.

## First 20 minutes
### Planck epoch

* c. 0 seconds (13.799 ± 0.021 Gya): Planck epoch begins: Big Bang occurs in which ordinary space and time develop out of a primeval state described by a quantum theory of gravity or "Theory of everything". All matter and energy of the universe is contained in a hot, dense point (gravitational singularity)

### Grand unification epoch

* c. 10$^{−43}$ seconds: Gravity separates and begins operating on the universe—the remaining fundamental forces stabilize into the electronuclear force, also known as the Grand Unified Force or Grand Unified Theory (GUT), mediated by (the hypothetical) X and Y bosons which allow early matter at this stage to fluctuate between baryon and lepton states.

### Inflation

* c. 10$^{−35}$ seconds: inflation, expands the universe by a factor of the order of 10$^{26}$ over a time of the order of 10$^{−33}$ to 10$^{−32}$ seconds. The universe is supercooled from about 10$^{27}$ down to 10$^{22}$ kelvin.
* c. 10$^{−32}$ seconds: Cosmic inflation ends.$^{:193}$ The familiar elementary particles now form as a soup of hot ionized gas called quark–gluon plasma;

### Quark epoch

* c. 10$^{−12}$ seconds: Electroweak phase transition: The weak nuclear force is now a short-range force as it separates from electromagnetic force, so matter particles can acquire mass and interact with the Higgs Field. The quark–gluon plasma persists (Quark epoch). The universe cools to 10$^{15}$ kelvin.

### Quark-hadron transition

* c. 10$^{−6}$ seconds: As the universe cools to about 10$^{10}$ kelvin, a quark-hadron transition takes place in which quarks become confined in more complex particles—hadrons.$^{:305}$

### Lepton epoch

* c. 1 second: Lepton epoch begins: The universe cools to 10$^9$ kelvin. At this temperature, the hadrons and antihadrons annihilate each other, leaving behind leptons and antileptons – possible disappearance of antiquarks. Gravity governs the expansion of the universe: neutrinos decouple from matter creating a cosmic neutrino background.

### Photon epoch

* c. 10 seconds: Photon epoch begins: Most leptons and antileptons annihilate each other. As electrons and positrons annihilate, a small number of unmatched electrons are left over – disappearance of the positrons.
* c. 10 seconds: Universe dominated by photons of radiation – ordinary matter particles are coupled to light and radiation.
* c. 3 minutes: Primordial nucleosynthesis: nuclear fusion begins as lithium and heavy hydrogen (deuterium) and helium nuclei form from protons and neutrons.
* c. 20 minutes: Primordial nucleosynthesis ceases

## Matter era
### Matter and radiation equivalence

* c. 47,000 years (z = 3600): Matter and radiation equivalence
* c. 70,000 years: As the temperature falls, gravity overcomes pressure allowing first aggregates of matter to form.

### Cosmic Dark Age

* c. 370,000 years (z = 1,100): The "Dark Ages" is the period between decoupling, when the universe first becomes transparent, until the formation of the first stars. Recombination: electrons combine with nuclei to form atoms, mostly hydrogen and helium. Ordinary matter particles decouple from radiation. The photons present during the decoupling are the same photons seen in the cosmic microwave background (CMB) radiation.
* c. 10–17 million years: The "Dark Ages" span a period during which the temperature of cosmic microwave background radiation cooled from some 4,000 K (3,730 °C; 6,740 °F) down to about 60 K (−213.2 °C; −351.7 °F).

### Reionization

* c. 100 million years: Gravitational collapse: ordinary matter particles fall into the structures created by dark matter. Reionization begins: smaller (stars) and larger non-linear structures (quasars) begin to take shape – their ultraviolet light ionizes remaining neutral gas.
* 200–300 million years: First stars begin to shine: Because many are Population III stars (some Population II stars are accounted for at this time) they are much bigger and hotter and their life cycle is fairly short. Unlike later generations of stars, these stars are metal free. Reionization begins, with the absorption of certain wavelengths of light by neutral hydrogen creating Gunn–Peterson troughs. The resulting ionized gas (especially free electrons) in the intergalactic medium causes some scattering of light, but with much lower opacity than before recombination due the expansion of the universe and clumping of gas into galaxies.
* 200 million years: The oldest-known star (confirmed) – SMSS J031300.36−670839.3, forms.
* 300 million years: First large-scale astronomical objects, protogalaxies and quasars may have begun forming. As Population III stars continue to burn, stellar nucleosynthesis operates – stars burn mainly by fusing hydrogen to produce more helium in what is referred to as the main sequence. Over time these stars are forced to fuse helium to produce carbon, oxygen, silicon and other heavy elements up to iron on the periodic table. These elements, when seeded into neighbouring gas clouds by supernova, will lead to the formation of more Population II stars (metal poor) and gas giants.
* 320 million years (z = 13.3): HD1, the oldest-known spectroscopically-confirmed galaxy, forms.
* 380 million years: UDFj-39546284 forms, current record holder for unconfirmed oldest-known quasar.
* 600 million years: HE 1523-0901, the oldest star found producing neutron capture elements forms, marking a new point in ability to detect stars with a telescope.
* 630 million years (z = 8.2): GRB 090423, the oldest gamma-ray burst recorded suggests that supernovas may have happened very early on in the evolution of the Universe

### Galaxy epoch

* < 1 billion years, (13 Gya): first stars in the central bar portion of the Milky Way are born,
* 2.6 billion years (11 Gya): first stars in the thick disk region of the Milky Way are formed.
* 4 billion years (10 Gya): Gaia Enceladus merges into Milky Way.
* 5 or 6 billion years, (8 or 9 Gya): first stars in the thin disk region of the Milky Way are formed.

### Acceleration

* 8.8 billion years (5 Gya, z = 0.5): Acceleration: dark-energy dominated era begins, following the matter-dominated era during which cosmic expansion was slowing down.

## Epochs of the formation of the Solar System

* 9.2 billion years (4.6–4.57 Gya): Primal supernova, possibly triggers the formation of The Solar System.
* 9.2318 billion years (4.5682 Gya): Sun forms – Planetary nebula begins accretion of planets.
* 9.23283 billion years (4.56717–4.55717 Gya): Four Jovian planets (Jupiter, Saturn, Uranus, Neptune) evolve around the Sun.
* 9.257 billion years (4.543–4.5 Gya): Solar System of Eight planets, four terrestrial (Mercury, Venus, Earth, Mars) evolve around the Sun. Because of accretion many smaller planets form orbits around the proto-Sun some with conflicting orbits – early heavy bombardment begins. A large planetoid strikes Mercury, stripping it of outer envelope of original crust and mantle, leaving the planet's core exposed – Mercury's iron content is notably high.
* 9.266 billion years (4.533 Gya): Formation of Earth-Moon system following giant impact by hypothetical planetoid Theia (planet). Moon's gravitational pull helps stabilize Earth's fluctuating axis of rotation.
* 9.271 billion years (4.529 Gya): Major collision with a pluto-sized planetoid establishes the Martian dichotomy on Mars
* 9.3 billion years (4.5 Gya): Sun becomes a main sequence yellow star: formation of the Oort cloud and Kuiper belt
* 9.396 billion years (4.404 Gya): Liquid water may have existed on the surface of the Earth
* 9.7 billion years (4.1 Gya): Resonance in Jupiter and Saturn's orbits moves Neptune out into the Kuiper belt causing a disruption among asteroids and comets there. As a result, Late Heavy Bombardment batters the inner Solar System. Meteorite impact creates the Hellas Planitia on Mars, the largest unambiguous structure on the planet.
* 10.4 billion years (3.5 Gya): Earliest fossil traces of life on Earth (stromatolites)
* 10.6 billion years (3.2 Gya): Martian climate thins to its present density: groundwater stored in upper crust (megaregolith) begins to freeze, forming thick cryosphere overlying deeper zone of liquid water – dry ices composed of frozen carbon dioxide form
* 10.8 billion years (3 Gya): Beethoven Basin forms on Mercury – unlike many basins of similar size on the Moon, Beethoven is not multi ringed and ejecta buries crater rim and is barely visible
* 11.6 billion years (2.2 Gya): Last great tectonic period in Martian geologic history: Valles Marineris, largest canyon complex in the Solar System, forms – although some suggestions of thermokarst activity or even water erosion, it is suggested Valles Marineris is rift fault.

## Recent history

* 11.8 billion years (2 Gya): Olympus Mons, the largest volcano in the Solar System, is formed
* 12.1 billion years (1.7 Gya): Sagittarius Dwarf Spheroidal Galaxy captured into an orbit around Milky Way Galaxy
* 12.7 billion years (1.1 Gya): Copernican Period begins on Moon: defined by impact craters that possess bright optically immature ray systems
* 12.8 billion years (1 Gya): Interactions between Andromeda and its companion galaxies Messier 32 and Messier 110. Galaxy collision with Messier 82 forms its patterned spiral disc: galaxy interactions between NGC 3077 and Messier 81; Saturn's moon Titan begins evolving the recognisable surface features that include rivers, lakes, and deltas
* 13 billion years (800 Mya): Copernicus (lunar crater) forms from the impact on the Lunar surface in the area of Oceanus Procellarum – has terrace inner wall and 30 km wide, sloping rampart that descends nearly a kilometre to the surrounding mare
* 13.175 billion years (625 Mya): formation of Hyades star cluster: consists of a roughly spherical group of hundreds of stars sharing the same age, place of origin, chemical content and motion through space
* 13.2 billion years (600 Mya): Whirlpool Galaxy collides with NGC 5195 forming a present connected galaxy system. HD 189733 b forms around parent star HD 189733: the first planet to reveal the climate, organic constituencies, even colour (blue) of its atmosphere
* 13.6–13.5 billion years (300-200 Mya): Sirius, the brightest star in the Earth's sky, forms.
* 13.7 billion years (100 Mya): Formation of Pleiades Star Cluster
* 13.780 billion years (20 Mya): Possible formation of Orion Nebula
* 13.792 billion years (7.6 Mya): Betelgeuse forms.
* 13.8 billion years (Without uncertainties): Present day.