The Big Bang Theory
The Big Bang is the creation of our universe. Everything was compressed into a very, very small area. We never knew if there was something before it. This event took place 10-20 billion years ago!
After compressing together so tight a the little particles begin to expand. The expansion starts very, very small making up the universe. After Millions of years earth was soon forming.
Current day the universe is still expanding. Due to the big band theory. All other galaxies appear to be moving AWAY from us ( as if propelled by a previous force a ). Oxygen has been going up since the past, letting more living things live rather than die for lack of oxygen.