The young earth theory falls apart when you look at the theory and evidence in toto and when one uses it for predictability.
When people want to find diamonds, fozzil fuels and minerals they use old earth theory because it works. One has great difficulty predicting with the young earth theory.
Young earth theory hypothesizes that the Grand Canyon was created in a very short time by a large amount of rapidly flowing water. YET proponents often point to the rapidly formed canyon that was created shortly after the eruption of Mt. St. Helens. These are some of the things one would expect to find from a rapidly formed canyon:
large number of large boulders, especially at the end of the canyon (downstream) (rapidly flowing water breaks off rock in larger pieces)
mostly rough edged rocks (no time to be worn smooth)
an extremely large delta (no time to be eroded away)
evidence of a large amount of water at the beginning of the canyon (upstream)
The Grand Canyon is lacking these pieces of evidence.
Another piece of damaging evidence is that there were two volcanic eruptions that caused lava to flow into the canyon and created large natural dams. If the canyon was formed in a very short amount of time, the amount of water flowing through the canyon would not have allowed the dams to form. Not only were the dams large enough to form large lakes but they were eroded to what are now a series of rapids.
Also, think about the amount of water that would be needed to form the Grand Canyon in a very short amount of time. The Niagara Falls has a tremendous amount of water flowing over it and it is not eroding very rapidly. Of course, now its flow is requlated by a Canadian-US group. But, if there was that much water to rapidly form the Grand Canyon it would have left much more evidence than just the Grand Canyon.
If Noah's flood did occurred there would be more than one Grand Canyon. The places where I would look would be China, Brazil, Australia, India and probably Central Europe. But when you look at those locations you see that other forces of nature than water were prominent in there formations. Northern China, for instance, was greatly shaped by winds depositing dust over a tremendously large amount of time.
The YET does not account for the formation of the Hawaiian Islands. The islands were formed as that area of the earth moved over a hot spot. The western Islands are older than the eastern islands. An a new island, Lo'ihi, is starting to form at the bottom of the ocean. Scientist estimate that the new island will reach the surface in 50,000-200,000 years. If YET is correct there should be only one or two Hawaiin islands of the same age.
The YET does not account for the formation of the series of caldera volcanoes in Western United States (From Washington to Wyoming). Yellowstone National Park is in the youngest of the calderas. This series was formed as the North American plate moved over a hot spot. The hot spot is now under Yellowstone National Park.
Now here is something interesting. The Grand Canyon and this series of calderas are relatively close together. Now if a large amount of water was in the area to form the Grand Canyon, these caldera's would show some evidence of this water. They don't. Now, if you hold to the YET and the hypothesis that the Grand Canyon was formed by large amount of water in a very short amount of time, you'll have to say that the caldera series was formed after the Grand Canyon was formed.
So, here's a scenario: A huge lake forms over western US and then rapidly drains to form the Grand Canyon. Then the continental plate rapidly moves 700 miles but stops periodically to allow a caldera to blow. Ok, but here's another piece of evidence to consider, the successive ash layers from each caldera eruption don't support this scenario.
Ok, new scenario: A huge lake forms over western US and then rapidly drains to form the Grand Canyon. Then the continental plate rapidly moves 700 miles but stops periodically to allow a caldera to blow, the ash to settle and to allow plant and animal life to firmly reestablish before the next caldera blows.
Now add the formation of the Hawaiian Islands, the rise and fall of the North American inland sea, the cratering of the moon, and other major geological and biological events. The Yough Earth Theory falls apart under the weight of evidence in toto.
For those who need to know, in toto means: completely or in total