The Big Bang
Many scientists believe that the Universe was created by a huge explosion called the big bang, which occurred 15,000 million years ago.
The First Atoms
Within minutes of the big bang the first atoms, the basis of all matter were formed.
The First Molecules
After about 10,000 years, temperatures of more than 10,000 million degrees forced atomic particles to come together to form the gases hydrogen and helium.
Gases Form Strands
About 700,000 years after the big bang, gases in space started to form into strands.
Gases Form Nebulae
About 1,000 years million years after the big bang, the strands of gases swirled together to form clouds of dust and gas called nebulae.
The First Stars
As the clumps of dust and gas in a nebula were drawn together by their own gravity, the increasing pressure made gases at the center very hot. Once the core reached 10 million degrees, nuclear reactions occurred and the stars were born.
Birth of the First Galaxies
About 1,500 million years after the big bang, the first galaxies were formed as spinning clouds of stars, dust, and gas.
Continually Expanding Universe
Scientists have proved that the galaxies of the universe are moving farther and farther apart. This means that the Universe is getting bigger and bigger.
The Big Crunch
Most scientists believe that the Universe will expand only so far. Once the energy from the big bang is used, it will fall inwards to a Big Crunch.
