The evidence against a global flood is extensive and convincing. Here is some of it:
1. The fossil record, which yields a record of life with a consistent pattern: more and more complex life forms appearing at progressively higher and newer levels. Burials for fish and mammals follows the same pattern of increasing complexity. A global flood theory requires the fossil record to be a somewhat haphazard jumble of odds and ends dumped by the flood, which is not the case.
2. There is no single, consistent, global, sedimentary flood layer.
3. The nature and composition of coal beds are not consistent with young earth and floodwater scenarios.
4. Thick salt bed formed by the slow evaporation of sea water (the Paradox Basin of Utah, where they reach a depositional thickness of 1.5 km with at least 29 separate cycles of salt deposition) is inconsistent with a theory that requires them to have formed in a single year (at a minimum rate of 4 m/day).
5. Typical ocean floors are covered by about 800 m of sediments. Assuming an average deposition rate of 0.01 mm/yr, an 800-meter accumulation would require 80 million years. Young earth creationists would require most of this accumulation to have taken place late in the flood year. The very delicate layering and fine grain size characteristic of these oozes and muds argue strongly against such wholesale and rapid dumping rates.
6. The top 2 km of Mt. Ararat’s 5.2 km height is a volcano built over deformed sedimentary rocks. Young creationists’ model requires that the entire volcanic growth took place very late in the flood year. This volcano had to violate all laws of thermal physics in order to cool completely in a few months in time for the ark to land on it.
7. Grand Canyon geology. For the Grand Canyon to have formed in one year would require massive layers of wet sediments to be deposited and hardened at astounding rates over the course of just a few weeks, leaving them solid enough to be incised into mile-high cliff by receding floodwaters. This could be true of limestone, but not of sandstone and shale, which require major loss of water, compaction and/or chemical cement to become a strong rock—all processes that involve significant amounts of time.
8. The examination of silt levels at the Sumerian cities of Ur, Kish, Shuruppak, Lagash and Uruk (all of which have occupation levels at least as early as 2800 BC) are from different periods (some from 4th millennium and some from 3rd) and do not reflect a single massive flood that inundated them all at the same time. Similarly, the city of Jericho, which been continuously occupied since 7000 BC, has no flood deposits whatsoever. Climatological studies have indicated that the period from 4500 to 3500 BC was significantly wetter in this region, but that offers little to go on.
9. Environmental Evidence:
a. According to Genesis, the sea level rose for 150 days until it covered the tops of the mountains, and then subsided for another 150 days. This is physically impossible. The local sea level can rise several feet an hour during a hurricane, but for the sea level to rise to the 17,000’ peak of Ararat it would have to rise to that height around the entire planet. That would require 620 million cubic miles of additional water weighing 3 quintillion tons. All the oceans of the world would have to triple in volume in only 150 days and then quickly shrink back to normal. Where did the water come from, and where did it go?
b. For the water to reach 17,000’ in 150 days, it would have had to rise at the rate of over 100’ per day, almost 5’ per hour. Even if that was possible, it would have created currents that would have made survival in the ark unlikely.
c. It has long been know that rain clouds cannot possibly hold even 1/10th of 1% of the water required for a flood of this magnitude.
d. If the ark ran aground on the still submerged summit of Mt. Ararat on the 17th day of the 7th month, and the tops of the mountains became visible on the first day of the 10th month, was water receded only 15’ in 75 days. Yet it would have to have receded 17,000 in the next 75 days, because by the first day of the first month, the earth was dry.
e. What did the carnivorous animals eat until their prey populations were reestablished?
f. If the dove flew down into a valley to get an olive leaf (only growing in low elevations), how did it manage to fly back up to 17,000’ to the ark? Doves can’t do that.
g. There are a number of animals that have been confined to local areas since before the Pleistocene Ice Age. If these (the kangaroos of Australia being an example) were to be brought to the ark in Mesopotamia and then released after the flood, it does not seem possible that they would or could migrate back to their previous locations without populating other parts of the world, especially since Australia is an island.
h. A universal flood would mix all salt and fresh water, killing all freshwater fish and some saltwater fish. Those would not have been on the ark.
10. There would not have been enough room in the ark to accommodate two of all the species then in existence. Fossil evidence around the globe shows that there was an abundant animal population in every continent. Plus, they had one week to get 42,000 on board. Even if God brought them to the ark, that’s a traffic jam that would take more than one week to unsnarl.
11. Assuming 21,000 species of amphibian, reptile, bird, and mammals, we’re assuming at least 42,000 on board. Of the 8 caretakers, each would have to visit 2637 cages a day for feeding and cleaning. If each person worked a 12-hr shift, each cage would get 3 2/3 minutes of care a day.
12. To cover mountains 6 miles high would require 8 times more water than we have on the planet. Where did it come from and where did it go? That much additional water, if created specially for the purpose, would have altered the earth’s weight and disturbed the earth’s orbit around the sun, as well as the moon’s orbit around the earth.
13. Though there are accounts of a great flood around the globe, the differences between them are too extensive to allow confident claims that they must be narrative reflections of the same event. Flood stories are entirely lacking in Africa, occur only occasionally in Europe, and are absent in many parts of Asia. They are widespread in America, Australia, and the islands of the Pacific.
Derek Kidner says, “In themselves, these verses [Gen. 7.19-24] are not decisive for or against a localized flood: even the whole heaven (19) is likely, on the analogy of these chapters, to be the language of appearance (Paul uses similar speech hyperbolically in Col. 1.23). The concern of the story is to record the judgment which man brought on his whole world, not to dilate on geography. The very fact that a single word in Hebrew normally serves for either ‘country’ or ‘earth’ reflects a practical rather than theoretical interest.”
(- Derek Kidner, Genesis, InterVarsity Press, 1967, p. 91)
Kidner continues:
“If we possessed no physical clues to the early history of the earth and of the primitive distribution of mankind, it would have to be left an open question whether such expressions in the flood story as "the earth", "all the high mountains under the whole heaven", and "all flesh", in Genesis 7:19, 21, were to be understood in their modern or ancient sense. As it is, the various geological data that have been thought to favor a strictly universal flood have been successfully found wanting, in the opinion of most experts, and little reasonable doubt remains (although some would dispute this) that the events of Genesis 6-8 must have taken place within a limited though indeed a vast area, covering not the entire globe, but the scene of the human story of the previous chapters. Some opinions confine this to Mesopotamia, others envisage a still larger tract; there is certainly room for further investigation.
“But it also appears, from the distribution and generally accepted dating of human remains, that certain branches of mankind had been settled in countries far beyond the specific Old Testament horizon since the Paleolithic age, and unless this world population was drawn back into the vicinity of Mesopotamia before the Flood, or unless the paleontological data needs drastic reinterpretation, it seems to follow that the destruction of life was, like the inundation of the earth, complete in the relative and not the absolute sense. By "relative" we mean related to the area of direct Old Testament interest. The record neither affirms nor denies that man existed beyond the Mesopotamian Valley. Noah was certainly not a preacher of righteousness to the peoples of Africa, of India, of China or of America—places where there is evidence of mankind many thousands of years before the flood. The emphasis in Genesis is upon that group of cultures from which Abraham eventually came. The language of this story is in fact the everyday language normally used in Scripture, describing matters from the narrator's own vantage-point and within the customary frame of reference of his readers.
"Whether this is the right assessment of the evidence or not, we should be careful to read the account whole-heartedly in its own terms, which depict a total judgment on the ungodly world already set before us in Genesis—not an event of debatable dimensions in the world we may try to reconstruct. The whole living scene is blotted out, and the New Testament makes us learn from it the greater judgment that awaits not only our entire globe, but the universe itself (2 Peter 3:5-7).”
(- Derek Kidner, Genesis, InterVarsity Press, 1967, p. 93-95)