1. The Big Bang occurred approximately 13.7 billion years ago, when the universe (which was nothing, just a point of infinite density at the time) exploded, exerting energy in all different directions and creating time and space. In a fraction of a second after the Big Bang, the universe grew rapidly to more than a thousand times the size of the sun.
2. After one second, the universe was a very hot swirling mass dominated space full of quarks (basic particles) and energy. The universe was very dense and opaque. The basic particles were formed from energy by Einstein’s equation E=mc^2.
3. After 500000 years, the universe had cooled down to a temperature of 3000 Kelvin. The protons, neutrons and electrons, joined together to form the first two types of atoms, hydrogen and helium.
4. After 1 billion years, the hydrogen and helium atoms began to form dense pockets of gas throughout the universe. The pockets of gas are known as protogalaxies ( a contracting swirling cloud of gas, which will eventually form a galaxy).
5. After 2 billion years, the protogalaxies gathered together into clusters of protogalaxies. Within the protogalaxies were gas concentrations which went on to give birth to the first generation of stars. Some of these first generation stars evolved into blue giants (stars which create bigger atoms by nuclear fusion and are known as “fast fusing”). When the blue giants near the end of their life cycle they merge into the “red giant stage”, which is followed by a supernova (death of a star). The supernovae exerted space with heavier atoms which allowed the existence of heavy planets.
6. After 5 billion years, all the first generation stars had reached the end of their life cycles and the centre of our current solar system (the sun) , had formed from the nova debris into a sun.