The universe started with the Big Bang approximately 13 BILLION years ago.
This establishes that we are talking about a LONG time.
The point here is to get you to start thinking in big numbers so that the earth's age can make sense.
The Big Bang is now well accepted among Cosmologists and Astronomers as being the event that initiated the universe.
No scientist will even hazard a guess as to what caused the Big Bang or what came before it.
All scientific research starts from the nanoseconds AFTER the Big Bang.
Cosmologists think they know what happened after the Big Bang - except for the first 10-to-the-MINUS-43rd-power seconds. During this period, called Planck time, space and time itself, the fundamental forces of nature and the laws of physics were still forming. After this time, cosmologists can apply knowledge of fundamental forces and laws to describe what happened next.
Hubble - The mirror on the Universe, Robin Kerrod, Firefly Press, 2003.
For a look at photos from the Hubble telescope, like the one below, look here: http://hubblesite.org/gallery/ Hubble Gallary>.