The Expanding Earth Model proves that the earth has expanded greatly in the past.  All of the Land Masses would fit together perfectly on a smaller planet.  Scientists don't know what caused this drastic expansion of the earth however this is from the Global Flood and most of the water came from the destruction of Tiament by Planet X.

A conservative estimate would make an increase in the diameter of about 5000 miles (7680 miles to 12,800 miles) and an increase of about 20 Quintillion Tonnes of Water to the earth.

The reason for the Atmosphere being twice as thick before the flood is because the amount of atmosphere is the same as it is now just thinned out so plants and animals do not get as large nor do they live as long.

The Blast Wave from the Micronova that occured at the first pass of Planet X can clearly be seen with the two massive areas of rapid desertification occurring with the Sahara and Gobi joined together and then Australian and Western North America.  If you pause the video at exactly the 1:00 mark you will see precisely where the moon was at the time the blast hit the earth - right between those two arid areas and forming a perfect circle on the face of the earth.

Source Video :

http://www.youtube.com/watch?v=oJfBSc6e7QQ