10^-43 seconds
Known as the Planck Era, this is the closest that current physics can get to the absolute beginning of time. At this moment, the universe is thought to be incredibly hot, dense and turbulent, with the very fabric of space and time turned into a roiling morass. All the fundamental forces currently at work in the universe - gravity, electromagnetism and the so-called strong and weak nuclear forces - are thought to have been unified during this stage into a single "superforce".
10^-35 seconds
The so-called Grand Unification Era, at the end of which the superforce begins to break apart into the constituent forces we see today. Around this time so-called inflationary energy triggers a dramatic burst of expansion, expanding the universe from far smaller than a subatomic particle to far larger than the cosmic volume we can see today. In the process, the primordial wrinkles in space-time are smoothed out.
10^-32 seconds
The energy dumped into the universe by the end of inflation leads to the appearance of particles of matter via Einstein's celebrated equation E=mc^2. Initially a mix of matter and antimatter, most of the particles annihilate each other in a burst of radiation, leaving behind randomly scattered pockets of matter.
10^-11 seconds
The so-called Electroweak Era, when the last two fundamental forces still unified with one another - electromagnetism and the weak nuclear force - finally split, leaving the universe with the four separate forces we observe today.
10^-6 seconds
As the universe continues to expand, it becomes cool enough to allow the familiar particles of today's matter, protons and neutrons, to form from their constituents, known as quarks.
200 seconds
At a temperature of one billion degrees celsius, protons and neutrons start to come together to form nuclei, the charged cores of atoms. Within 20 minutes, the temperature of the universe has become too cold to drive the process, which ceases with the formation of the nuclei of hydrogen and helium, the simplest and most common chemical elements in the universe. The formation of all the other elements - including the carbon, oxygen and nitrogen needed for life - will emerge with the first massive stars millions of years later.
300,000 years
The universe has cooled to about 1,000C - cool enough for electrons to pair up with nuclei to form the first atoms. By the end of this so-called Recombination Era, the universe consists of about 75% hydrogen and 25% helium. With the electrons now bound to atoms, the universe finally becomes transparent to light - making this the earliest epoch observable today.
200m years
Small, dense regions of cosmic gas start to collapse under their own gravity, becoming hot enough to trigger nuclear fusion reactions between hydrogen atoms. These are the very first stars to light up the universe.
0.5bn - 1bn years
The force of gravity starts to pull together huge regions of relatively dense cosmic gas, forming the vast, swirling collections of stars we call galaxies. These in turn start to form clusters, of which one - the so-called Local Group - contains our own Milky Way galaxy.
9bn years
The force of gravity trying to slow the cosmic expansion begins to lose out to the anti-gravitational effect of "dark energy", a mysterious force which has been accelerating the cosmic expansion ever since.
9.1bn years
A region of gas and dust from exploding stars in the Milky Way galaxy starts to collapse under its own gravity, forming a small star surrounded by a disk of rocky material and gas. Swarms of giant chunks of debris form within the disc, collide and merge - forming the Earth, moon and other planets.
