Sequences of Fossils in Sedimentary Rock Layers
K-Pg Asteroid Strike
The Tanis K-Pg Event Site
More Findings from the Tanis Site
Other Dinosaur Finds: Tracks, Eggs and Feces
Location of Dinosaur Fossils in the Rock Layers: Is a Recent Global Flood Credible?
More on Paleosols and Vertebrate Burrows
Closing Thoughts on Significance of the Tanis Site
Sequences of Fossil in Sedimentary Rock Layers
When canal builders surveyed the rocks of Britain in the early 1800s, they noticed that certain fossils only appeared in certain layers, and that the order of these fossils from layer to layer was typically the same all over the country. The same tendency of a well-defined sequential order in fossilized species has been found to hold all over the world. For instance, rock layers containing trilobites are found below, never above, layers containing modern clam species. Rocks with horse fossils are found above, never below, rocks containing dinosaur bones. Well before Darwin published his Origin of Species in 1859, it was realized that this pattern of fossils showed that the sedimentary rock layers were not the result of a single, year-long global Flood. Rather, these layers were deposited over many years, and the species of plants and animals alive at any one time changed from one age to another.
Fossils which have a wide geographic distribution but a relatively short time of appearance in the rocks are called “index fossils”, since they are useful in determining the relative ages of the rocks in which they occur:
The index fossils shown here were all sea creatures, so this rigorous ordering cannot be the result of, say, fleet-footed clams getting buried in higher rock layers because they ran to higher ground as the Flood-waters rose while the plodding trilobites were left behind to be buried first.
At all levels of rocks there are fossils of animals that are big and small, skinny and fat, so this sequence is not a result of hydrodynamic sorting during one big Flood. Rather, the order of their world-wide appearance in the rock layers reflects their actual temporal appearance, then disappearance, across the times of deposition in the sedimentary rocks in which they are found. As noted in Simple Evidences for Old Earth, geologists find many features that cause them to believe that these deposition times extended over millions of years. These features include angular unconformities, and thick limestone layers and caves in the midst of the rock layers.
In any given locality, it is often possible to identify several distinct rock layers (“formations”), with their characteristic fossils. A sequential set of perhaps five to fifty formations might be conceptually grouped together in a “period”. The geologic time spanned by a period is typically tens of millions of years, as determined by various physical markers . The end of some periods are marked by widespread extinctions of species, with the subsequent appearance or expansion of different types of species.
Here is a list of the geological periods that span the past half billion years:
A number of clearly identifiable animal forms, such as arthropods and mollusks and primitive jawless fish, first appear in the Cambrian period. Fossils of jawed fishes are evident in the Silurian period. Many varieties of fish flourished during the Devonian (the “Age of Fishes”). During the Devonian, too, the first tetrapods (amphibians, at this point) appeared. A number of tetrapod-like fishes and fish-like tetrapod fossil intermediates are known from this time, illustrating the evolutionary development of amphibians . Reptiles first appeared in the Carboniferous period. They were effective herbivores and carnivores, and became the dominant animals on land and in the oceans and the skies during the Mesozoic era (the “Age of Reptiles”), comprising the Triassic, Jurassic, and Cretaceous periods. Dinosaurs, including familiar names such as stegosaurus, triceratops, and tyrannosaurus, ruled every continent during the Jurassic and Cretaceous periods.
Mammals arose during the Mesozoic era, but were overshadowed by the dinosaurs. A sequence of fossil intermediates between distinctive reptilian and mammalian jar and ear structures supports a gradual evolutionary transition between reptiles and mammals. Most early mammals were small insectivores or omnivores. They stayed in burrows during the day, presumably hiding from reptile predators, and crept out at night to feed. ( The rest of this article on dinosaur fossils goes on for many pages. To see other articles on this blog, look for recent titles listed along right-hand side of screen, or go here for listing of articles by topic. )
K-Pg Asteroid Strike
Dinosaurs abruptly vanish from the fossil record on every continent at the end the Cretaceous, along with some 75% of all land and sea plant and animal species. With the exception of some sea turtles and crocodiles, no tetrapods weighing more than 25 kilograms (55 lb) survived. This catastrophe is known as the K-Pg or K-T extinction event: “K” and “Pg” are abbreviations used for the Cretaceous and Paleogene periods. It is dated to about 66 million years ago. Before around 2000 when a nomenclature change was agreed on by the geology research community, the geological stratigraphic range that we now term the Neogene and Paleogene periods was called the “Tertiary”, and the upper boundary of the Mesozoic era was thus known as the “K-T” boundary, but current nomenclature is K-Pg.
There may be multiple factors that drove this mass extinction, including massive volcanic eruptions in the Deccan Traps in the Indian subcontinent. It is generally agreed, though, that a key driver was the large Chicxulub asteroid strike in the Yucatan area of Mexico. This impact was massive enough carve a crater some 110 miles (180 km) wide and to send up a giant cloud of incandescent debris to the northwest which probably incinerated the surface of western North America. What seems to have wreaked havoc worldwide was the dust sent into the atmosphere, which shut down photosynthesis for months or years thereafter. There were hundreds of feet of calcium sulfate (gypsum) rocks where the asteroid struck; when those rocks were vaporized by the impact, the result was a fine aerosol of sulfuric acid which blocked the sun and caused acid rain.
A large amount of melted rock was ejected into the atmosphere, and rained down in the form of small glassy blobs (tektites) hundreds and thousands of miles away from the impact site. Tektites from this asteroid have been found at various sites, though with time and water exposure the original glassy material often decomposes into clay. Some asteroids are relatively rich in the element iridium, which is nearly absent from rocks on earth. An iridium-rich layer of dust (transformed into a clay layer) has been found in many locales around the world at sites which are dated by other means to around 66 million years ago. The Ir-rich clay typically lies above the clay derived from the tektite ejecta; the millimeter-sized ejecta would have mainly fallen out of the towering impact blast cloud within 1-2 hours, whereas the Ir-rich dust settled over a longer timeframe. The clay layer formed by the decomposed and compacted fallout from the impact is also referred to as “tonstein”.
Below is an example from the K-Pg boundary visible near Dogie Creek, in eastern Wyoming. The K-Pg boundary layer here has two intervals. The black arrow points to the contact of the two intervals. The lower interval contains visible spherules which have all the characteristics of Chicxulub impact spherules, but these have been altered to goyazite (hydrous strontium aluminum phosphate) in their rims. The upper interval contains shocked quartz and a high concentration of iridium. The pollen in the boundary layer consists almost entirely of fern spores.
Above the Ir-rich K-Pg layer, worldwide, no dinosaur fossils have been found.  While many dinosaurs in the Americas may have died in conflagrations immediately associated with the asteroid impact, presumably the worldwide extinctions were due to herbivores starving due to the shutdown of photosynthesis, followed by carnivores starving for lack of prey. With the removal of dinosaurian competitors, mammals diversified and enlarged during the Cenozoic to become the dominant land animals. For instance, a fairly complete set of fossils documents the evolution of modern grass-eating horses from early Cenozoic twig-nibblers that were about the size of a fox.
The lush Mesozoic stands of angiosperm and gymnosperm terrestrial plants vanish at the K-Pg boundary. In many places on the planet, ferns were practically the only plants growing for many years after the K-Pg event. This shows as a “fern spike” in the sediments at or above the boundary. Ferns have been observed in modern times to be among the first plants to become established following volcanic eruptions that destroyed all local vegetation. The figure below for a New Zealand site, on the other side of the globe from the Yucatan impact site, depicts the relative abundance of spores and pollen from different types of plants below and above the K-Pg boundary. This boundary is identifiable by a spike in Ir and in Co, which are more common in asteroids than on the earth’s surface. Below the boundary, gymnosperms (mainly conifers) dominate, along with some angiosperms (flowering plants or trees), with relatively little sign of ground ferns. Immediately after the K-Pg event, ground ferns and then tree ferns proliferate, while other types of plants nearly disappear for some time. The sudden replacement of other pollens by fern pollens is observed world-wide, and typically in rock layers that sit atop hundreds or thousands of feet of prior sediments. These features are consistent with slow accumulation of these sediments over many years as plant ecosystems on the land wax and wane. They are not consistent with these all these sedimentary layers being laid down rapidly in the middle of a year-long worldwide Flood.
A geological map of Montana is shown below, showing surface exposures of rocks from various eras.
The Precambrian (mainly Proterozoic) sedimentary layers in the western part of Montana can be 35,000-50,000 feet thick. Paleozoic rocks are up to 10,000 feet thick, though these layers have been eroded away in most places and also buried under later sediments. Sedimentary layers that are relatively younger (Mesozoic, Cenozoic) are exposed in the eastern part of the state, again through erosion. During the Mesozoic era, highlands in the western part of the state were eroded down and about 5000 feet (1500 m) of sedimentary rock were deposited across the eastern half of the state. These include formations that are famed for dinosaur fossils, such as the Hell Creek formation at the very top of the Cretaceous in eastern Montana, and the Morrison formation at the top of the Jurassic in south-central Montana and in states to the south. Up to 4000 feet (1200 m) of sedimentary rock deposited during the Cenozoic, as mountain-building uplifts in western Montana contributed more sediment to be deposited in the flat lowlands in the east that were then near sea level. Much of the Cenozoic rock has since eroded away, as this area of the High Plains became elevated well above sea level.  The K-Pg boundary in Montana would typically be found at the interface between the green (Mesozoic) and yellow (Cenozoic) color-coded areas in the map above.
Here are some of the identifiable formations within these sedimentary layers in southeast Montana. The Hell Creek Formation is highlighted with a blue box. Many dinosaur fossils have been recovered from Hell Creek layers, including a Tyrannosaurus rex and a hadrosaur which preserved some flexible tissue within their femurs. We have discussed these specimens in “ Dinosaur Soft Tissue “. The K-Pg Ir-spike boundary is typically found between the Hell Creek and Fort Union formations or within the upper portion of the Hell Creek formation. 
Here is a photo of the K-Pg boundary layer between the Hell Creek and the overlying Fort Union Formation at Mud Buttes, in southwest North Dakota, just across the border from eastern Montana. There is a lower pinkish boundary clay, formed from low-angle ejecta from the asteroid strike. Above that is a 1-cm-thick ( 0.4 inch) pinkish clay layer (low angle ejecta), overlain by a 3-cm-thick (1.2 inch) orange layer containing altered spherules, derived from high angle ejecta that arrived at this site later. The top portion features shocked quartz and the maximum concentration of iridium. A small burrow has been dug into the top portion, presumably by a worm or insect. This 2-inch thick layer of clay and spherules marks the day, probably the very hour, when the age of reptiles ended and the era of mammals began.
The Tanis K-Pg Event Site
Maverick paleontologist Robert DePalma has identified and excavated an unusual site at the top of the Hell Creek Formation in eastern Montana. He has operated mainly on his own, without the usual support from large institutions. His colorful story is told in a recent New Yorker feature article by Douglas Preston, and summarized in a Wikipedia draft article . DePalma has published or presented several notable findings in the past, including the first amber-trapped insect from the Hell Creek, and a tyrannosaur tooth embedded in a hadrosaur tail, indicating that tyrannosaurs were indeed hunters rather than merely scavengers.
The site, which DePalma has dubbed “Tanis” (evoking the ancient Egyptian site in “Raiders of the Lost Ark”) appears to contain deposits from tsunamis caused by the K-Pg asteroid impact. Thus, the fossils in these sediments were entombed on the very day of the impact. DePalma has published some key findings in a recent PNAS article, with a set of highly respected co-authors, including Walter Alvarez. Walter Alvarez, along with his father Luis, proposed back in 1980 that the K-Pg extinctions (then called K-T) were due to a large impactor, whose Ir signature might be observable in the K-Pg boundary layer. What follows are several figures from that PNAS paper, and from its Supplement .
Figure 1 (above) depicts and reconstructs the event site and its sediments. Frame (A) shows the location of the Tanis site, and its position relative to the interior seaway at the time. (B) shows a side photo of the site, with and without lines which trace out the sediment beds. As shown in (C), there was a regular sort of river flowing mainly eastward, toward the finger of ocean (Western Interior Seaway, WIS) which was present east of the Tanis site. The river channel was incised into bedrock, and a “point-bar” sandy deposit was present along one side of the channel. Such point bars are commonly observed on the inside of the loops of meandering rivers today. This point bar deposit is shown in yellow. The event deposit is shown in magenta. This deposit is about 1.5 m (4.5 ft) thick. Analysis of its layers indicates that it resulted from two massive flood waves which rolled up the river channel from the ocean. As these waves receded, they left a mass of dead fish amongst the sand and mud sediments. (See Figure S23 in the Supplement for a mash-up of these fish remains, oriented in the direction of flow). Here is the original caption for this Figure 1, slightly edited:
Original Figure 1 caption: Map of the Tanis study locality. (A) Tanis within a regional context (large map) and on a national map (Inset). Black dots in Inset are previously documented KPg tsunami localities; star denotes Tanis. Kf, Fox Hills Formation; Kh, Hell Creek Formation; Kp, Pierre Shale; Qor, Holocene; QTu, Quaternary and Upper Tertiary; Tp, Slope Formation. (B) Photo and interpretive overlay of an oblique cross-section through Tanis, showing the contact between the angled point-bar sandstone and the gray Hell Creek bedrock. (C) Simplified schematic depicting the general contemporaneous depositional setting for the Event Deposit (not to scale). The Event Deposit (1) covers the slope of a prograding point bar of a meander (2), which incised into the Hell Creek bedrock during the late Cretaceous. Location of the densest carcass accumulations (3) along the slope; location of KPg boundary tonstein directly overlying the Event Deposit (4); location of KPg tonstein overlying the adjacent overbank (5); location of Brooke Butte (6), the closest KPg outcrop to Tanis.
Rivers erode material in steeply-sloping highlands, and deposit some of this material in the flatter alluvial plains downstream. Periodic local flooding of rivers helps move material out of the river bed and onto the surrounding floodplain. The Hell Creek Formation was deposited in such an alluvial setting . DePalma et al. observe that the (relatively small) Tanis event deposit is much different than the usual Hell Creek formation sediments:
In modern fluvial depositional environments, as with the Hell Creek Formation, major high-energy depositional events or hydrological surges are related either to massive storms or to river flooding. The sedimentological features at Tanis, particularly the large-scale bidirectional flow, high runup, thick deposit, and draped sediment package of relatively even thickness, are incompatible with storms and river flooding and do not ally with other common terrestrial or marginal-marine depositional mechanisms such as tidalites. The depositional mode and sedimentology at Tanis compare most favorably with an inundation surge, with the physical characteristics of a tsunami that could have emanated from the impact site up the WIS or, alternatively, due to a more localized seiche. The large inland-directed surge complex at Tanis, incompatible with either river flooding or storm deposits, was a rare and unusual occurrence in the Hell Creek Formation.
Figure 2 (not shown here) in the paper displays many details about the layers and sublayers which comprise the event deposit.
The Chicxulub asteroid impact generated giant tsunamis, which left traces around the Caribbean and Gulf of Mexico areas. A normal tsunami would take at least 18 hours to travel along the surface of the water from the point of impact to the Tanis site. However, the millimeter-sized ejecta from the Chicxulub asteroid strike would have nearly all finished falling by 1-2 hours after the impact. Thus, the water surges that deposited the sediments at Tanis could not have come from a tsunami rolling all the way up the interior seaway. The preferred explanation at this point is that the massive earthquake resulting from the impact led to the water surges in the vicinity of the Tanis site. This type of seismic water surge is called a seiche.
The timing for the seismic waves to propagate through the earth to reach the Tanis area works out to match the timing of the ejecta falls. The phenomenon of a far-distant earthquake causing a substantial water surge has been observed on occasion. For instance, the large 2011 earthquake in Japan caused a 1.5 m (5 ft) seiche in a Norwegian fjord some 5000 miles away.
Below are sections A-E of Figure S1 in the Supplement. Section A shows the upper surface of the Event-Deposit, topped by an Ir-rich K-Pg claystone layer (“Tonstein”) which is a little over 1 cm (0.4 inch) thick, and then a carbonaceous shale layer rich in fern spores (“fern spike”). Section B shows a similar stratigraphic section from a nearby site (Mud Buttes, S.D) where the K-Pg boundary is also exposed . That site also shows the K-Pg tonstein layer, and the fern-spore-rich carbonaceous shale. However, the formation just below the tonstein at Mud Buttes is an ordinary paleosol (i.e. a soil layer, which has been buried under later sediments). The “TP” arrows in the profile point to “Terrace Paleosols” on the upper surface of the Tanis point-bar sandy deposit. These are relatively flat spots on the sandbar where enough soil developed to support some local small animal life. Among these structures are found burrows made by vertebrates (shown in section C), and by invertebrates such as insects (D). The oxidized walls of these burrows indicate that they had exposed to the air for a considerable time before the event surge came and filled them with sediment.
The original caption for this Figure S1 is: The Event-Deposit forms a drape of relatively even thickness, sharply overlying the angled point-bar slope, and is capped by a thin layer of tonstein overlain by a fern spore-dominated horizon (A), indistinguishable from Mud Buttes (B), and common for the Western Interior. Terrace paleosols (TP) underlying the Event-Deposit bear abundant pedogenic structures such as (C) vertebrate burrows, (D) invertebrate ichnofossils, and (E) oxidation halos, indicating prolonged subaerial exposure and occupation prior to inundation. Tunnels of insect burrows (D) are filled with sediment contiguous with the basal Event-Deposit and bear reddened oxidized walls, indicating subaerial exposure and open chambers up until the time of inundation.
What about all the millimeter sized spheroids from the asteroid impact that we see in other K-Pg sites? It turns out that these particles were raining down during the two water surges which laid down the event deposit. After the first surge (which deposited “Unit 1” of the event deposit) had receded or was receding, there was a brief time when it presented a soft wet silty surface to the sky. At that point, a number of ejecta spheroids came whizzing in at terminal velocity and thunked into the soft sediment near the top of the Unit 1 layers, warping the layers of existing sediment as they buried themselves several centimeters deep in their “craters”. These craters where quickly filled in by sediments in the second water surge, which laid down the Unit 2 layers. Figure 4 from the paper, shown below, has a cross-section (“E”) illustrating such an impact. The spherule is still visible (black arrow). In addition to these impacted spherules, some ejecta particles were concentrated in a few particular levels of Unit 2 sediments. This figure shows where these “lenses” of ejecta were found. Section A of this figure (with zoomed-in views in B and C) shows one of these lenses. Section D is a thin section micrograph.
More Findings from the Tanis Site
A great number of fishes were swept inland with the tsunami surges, and died as they were caught up in the silt-laden water and stranded in shallow, receding waters. As some of these fish were frantically pumping water through their gills, they took in many of the ejecta spheroids which were raining down into the water at the time. These spheroids can be seen in X-ray sections of the gill sections of these fish, as shown in Figure 6 of the main paper. Figure S15 in the Supplement (shown below) shows some of these spheroids which were visible in fish gills, in the field excavations. Section A of this figure shows DePalma pointing to a paddlefish fossil imprint which is being unearthed. We added a red arrow pointing to the gill region, just behind the curved jaws. Section E below is a view zoomed in on this gill region, clearly showing the spheroids concentrated there.
The DePalma PNAS paper notes that some tektites were trapped in amber in blobs along tree trunks. Being thus protected from chemical contact with the environment, these tektites were preserved in a relatively unchanged state.
In a 2017 presentation Robert DePalma described another intriguing finding: a mammal burrow which had been dug down into the Tanis event deposit from above, with bones of the mammal still in it. 
A long-standing controversy in the extinction of the dinosaurs is the “3-meter problem”. This is the observation that fossil remains of dinosaurs have not generally been found in the three meters (ten feet) of late Cretaceous rock just below the K-Pg boundary. This has led to speculation that dinosaurs had already died out before the K-Pg event. However, at least one dinosaur fossil has been found a mere 13 cm below the K-Pg boundary, so it seems that this 3 meter dearth of fossils does not reflect actual extinction.
In the PNAS article, DePalma et al. report the finding of a ceratopsian hipbone at the top of the event deposit (see Figure S29 in the Supplement). The owner of the hipbone had died some time before the Tanis water surges, yet this find suggests that dinosaurs were still alive around the time of the K-Pg event.
The New Yorker article claims that far more dramatic dinosaurian remains have been found in the lowest level of the Tanis event deposit:
At the bottom of the deposit, in a mixture of heavy gravel and tektites, DePalma identified the broken teeth and bones, including hatchling remains, of almost every dinosaur group known from Hell Creek, as well as pterosaur remains, which had previously been found only in layers far below the KT boundary. He found, intact, an unhatched egg containing an embryo—a fossil of immense research value. The egg and the other remains suggested that dinosaurs and major reptiles were probably not staggering into extinction on that fateful day. In one fell swoop, DePalma may have solved the three-metre problem and filled in the gap in the fossil record.
DePalma says that these results will be disclosed in future refereed publications. The purpose of the April, 2019 PNAS article was just to describe the geological setting of the Tanis deposits.
Other Dinosaur Finds: Tracks, Eggs and Feces
Many traces of dinosaurs besides their bones have been found in Mesozoic rocks. Tracks made by dinosaurs walking on soft ground have been discovered in various parts of the world, including sites close to Montana. Here is a track of dinosaur footprints in the Hell Creek Formation at a site in South Dakota, along the eastern border of Montana  :
The tracks below were found in the Morrison Formation at Dinosaur Ridge in central Colorado, south of Montana. The Morrison Formation is late Jurassic, dating to about 150 million years ago, some 80 million years younger than the Hell Creek. As might be expected from this time difference, the species of dinosaurs found in the Morrison (e.g. Stegosaurus, Brontosaurus/Apatosaurus, and carnivorous Allosaurus) differ from those commonly found in the Hell Creek (e.g. Triceratops and carnivorous Tyrannosaurus).
Dinosaur Eggs and Nests
Fossilized dinosaur eggs and nests have been found in various locations, including the Two Medicine formation in northwestern Montana. These finds include eggs with embryos in them, and nests with young hatchlings. The Two Medicine Formation, which is up to 2000 ft (600 m) thick, is dated to about 71-83 million years ago, or a few million years before the Hell Creek Formation in eastern Montana. Here is a clutch of fossilized Troodon eggs in a nest found in the Two Medicine Formation.
Fossilized Dinosaur Dung (Coprolites)
Fossilized feces are called coprolites. It takes unusual conditions for the relatively soft feces on the ground to become mineralized, but it does happen. It requires the feces to be deposited intact on the ground, and then covered over by sediment. If a dinosaur evacuated its intestines while being swirled away in a global Flood, the fecal matter would disintegrate.
Analysis of coprolites gives valuable information on animal diets. Dinosaur coprolites have been found in many locales, including Montana’s Two Medicine Formation. This 18 inch (44 cm) long specimen from the Frenchman Formation in southwest Saskatchewan (just north of Montana) is attributed to Tyrannosaurus rex :
Location of Dinosaur Fossils in the Rock Layers: Is a Recent Global Flood Credible?
The Rise of Modern Young Earth Creationism
By 1840, nearly all practicing geologists (many of them devout Christians) concluded that the earth was far older than the 6000 year age indicated by a literal interpretation of the Genesis chronology. Features in the sedimentary rock layers such as angular unconformities could not have formed as part of a year-long global Flood.
From about 1860 to 1960, nearly all Christians in Europe and North America, from the most liberal to the most conservative, were reconciled to an earth that was many millions of years old. Fundamentalist Protestants mainly subscribed to the “gap” theory, whereby a gap of millions or billions of years was held to interpose between Genesis 1:1 and 1:2. This interpretation, popularized by the Schofield Bible notes, accommodated a very old earth, while allowing for recent creation of the human race. W.B. Riley, editor of The Christian Fundamentalist and president of the Anti-Evolution League of America, stated in the 1920’s that there was not “an intelligent fundamentalist who claims that the earth was made six thousand years ago; and the Bible never taught any such thing”.
This all changed with the 1961 publication of Whitcomb and Morris’s The Genesis Flood, which promoted a young (6000 year old) earth. The book claimed that the entire surface of the world was scoured by a global Flood about 4500 years ago, which covered the highest mountains and deposited stupendous amounts of sediments. As described in Exposing the Roots of Young Earth Creationism, the scientific picture in Genesis Flood was largely lifted from a bogus Noahic Flood geology devised by Adventist George McCready Price. He, in turn, was driven to devise this Flood geology due to his adherence to a cult prophetess who claimed that God showed her visions of a literal worldwide Flood.  Although this Flood geology was contradicted by many clear evidences of an ancient earth , Young Earth (YE) creationism was enthusiastically embraced by many conservative Protestants, particularly in North America. Something like 20%-40% (depending on how the questions are phrased) of Americans believe that the earth and its plants and animals were formed less than 10,000 years ago. Citizens who care about science literacy are naturally concerned about this outcome.
Organizations such as Answers in Genesis and Creation Ministries International currently publish books, journals, magazines and web articles to promote YE creationism. The evidences for a young earth presented by these groups seem convincing to eager laymen, though these evidences fall apart upon close inspection.
When young Christians who have been told that a young earth view is an essential part of the faith eventually realize that that view is based squarely on falsehood, the impact on their faith can be devastating. Geology and biology professors report disillusioned YE creationist students coming to their office in tears. YE creationism also skews the dialog between believers and nonbelievers. Besides providing insufficient grounds for faith, it provides unnecessary grounds for skepticism. Scientifically literate people will be unable to give the gospel a fair hearing, if they are told that a recent, sudden creation is an essential part of Christianity .
What Would Flood Geology Deposits Look Like?
In Flood geology, the main sedimentary rock layers were all laid down in a roughly one-year Flood, which occurred about 4500 years ago, and about 1500 years after the creation of the world. For forty days, the Flood waters rose upon the earth from rainfall and from subterranean water sources, until all dry land was covered. The waters stayed above the highest mountains for 150 days, and then started to slowly recede. Some months later appreciable dry land appeared.
Where the rock layers are many thousands of feet or meters deep, the rate of deposition must have been very high. Arguably the sea level may have sloshed back and forth during the first forty days, occasionally exposing the surface of the sediments and leading to variable deposition rates, but something like a foot an hour (24 feet per day) would be a typical average rate for the Flood year to account for the mile-thick thickness of sedimentary rock layers in many areas of North America to accumulate in one year. After the first 40 days, there was no exposure of any dry land for at least 150 days. In Eastern Montana, where the sedimentary rock layers are more like 4 miles thick, the average deposition rate for a year would be some 100 ft (30 m) per day.
Some general chronological groupings of fossil-bearing sedimentary rocks recognized by geologists include the Precambrian formations, and the Paleozoic (540-250 M years ago), Mesozoic (250-66 M years ago), and Cenozoic (66 Mya–present) eras. YE creationists often acknowledge the existence of these general groupings, although they dispute the ages assigned to them. They typically assign the Paleozoic and Mesozoic layers to deposits from the Flood. There is not unanimity on where the Flood deposits start and end. In western Montana, the Precambrian rocks are up to 35,000-50,000 ft (up to 10 miles) thick. There seems to be no reasonable way these could have deposited in the scant 1500 years that the earth existed before the Flood. Likewise, in eastern Montana there are some 4000 ft (1.2 km) of Cenozoic sediments overlying the Mesozoic layers. Again, this seems difficult to account for unless the Flood activity is extended well into the Cenozoic layers.
After the first, say, 1000 feet (300 m) of sediment have been deposited for hundreds of miles in every direction, it would be safe to assume that all terrestrial vertebrates have been eliminated from that region, by being swept away or buried. Thus, in that region, we would not find evidences higher up (in the middle of thousands of feet of rock layers) of soil formation, or of large vertebrates digging burrows, laying eggs in nests, or defecating on the ground. But that is just what we do find. We have described the evidences for large animals, especially dinosaurs, doing all these activities, living out their normal life activities on a more or less dry land surface.
Comparing Flood Geology Expectations to Reality for Eastern Montana Rock Layers
The figure below shows what Flood geology would predict for the rock layers in eastern Montana. As noted earlier, the Paleozoic rock layers there are up to 10,000 ft thick. These deposits extend for hundreds of miles in all directions. After the first thousand feet or so of Flood sediments had deposited, surely all large terrestrial animals in the region were dead. Also, after the initial stage (first 40 days) of the Flood, no land was exposed for at least 150 days, and probably much longer.
Therefore, within the Mesozoic rock layers, there cannot be any evidence of large land animals performing their normal activities on the ground, such as walking around, making nests and laying eggs, defecating, or digging burrows. But, as noted above, that is exactly what we find in these rock layers. This completely invalidates Flood geology. There are many other lines of evidence which further disprove Flood geology and a young earth.
The general pattern of skeletal fossils likewise does not match expectations from a global flood. If great walls of water swept across the entire North American continent, sweeping away all terrestrial plants and animals, nearly all of these plants and animals should have been buried in the very lowest Paleozoic rock layers. The upper Paleozoic and the Mesozoic layers, thousands of feet above, should be essentially devoid of plant and animal fossils. But that is not what we actually find.
There are no terrestrial animal fossils at all in the lowest Paleozoic layers (e.g. Cambrian, Ordovician, Silurian), and when these fossils do appear in the higher layers, they are not all jumbled together as expected from a great Flood. YE creationists invoke mechanisms such as ecological zones or hydrodynamic sorting to explain the observed ordering of animals, but these fail to account for the fossils which are actually there. See The Grand Canyon, Monument to an Ancient Earth for a complete discussion of how the YE creationist attempts to explain the observed fossil order and geographical distribution in terms of a global Flood do not succeed. Although hippopotami and some dinosaurs are both large, swamp-dwelling animals, their fossils are never found buried together.
More on Paleosols and Vertebrate Burrows
Geologists can distinguish soils from plain sand or silt deposits by various physical and chemical characteristics. It typically takes many years to develop deep soils with characteristic soil horizons. Yet just such soils (paleosols) are found in the midst of thousands of feet of sedimentary rock layers (see here, here, and here). Here is an example of a well-developed paleosol (the brownish layer across the middle of the photo) in the Morrison Formation which dates to about 150 million years ago and extends over Colorado, Wyoming, and southern Montana. In this layer are whitish fossilized burrows made by vertebrates. All this simply could not happen under the raging sea while many feet per day of sediment are raining down, and thus the existence of these paleosols and burrows invalidate the notion that the sedimentary rock layers were deposited during a recent worldwide Flood.
Only a long sequence of events can account for this formation. Thousands of feet of sediments were deposited, covered by more sediments, to turn them into rock. Then this formation was lifted above sea level by plate tectonic motion, and the rocks eroded down. Erosion formed a layer of soil, and some animals lived there and dug burrows. Later this area got covered with water again, and more thousands of feet of sediment were deposited, and eventually turned to rock. Once again, this area was raised out of the sea and the solid rock eroded down to the present level.
Closing Thoughts on Significance of the Tanis Site
The K-Pg asteroid impact led to a catastrophic set of extinctions, killing off nearly all the large reptiles which had dominated land and sea. These extinctions in turn cleared the way for the rise of mammals, including primates and ultimately humans. Most sites which preserve a record of the K-Pg impact show only a snapshot, only a thin layer of ejecta and dust fallout. The deposit at the Tanis has been described as more like a high definition video recording – – it furnishes a unique record of the events of that asteroid strike as they unfolded minute by minute at that site, and it provides a diverse sampling of the flora and fauna which were alive on that very day.
The observations from the Tanis site reinforce the general pattern of physical evidence which is consistent with an old earth, not a young earth. The Hell Creek Formation lies atop many thousands of feet of prior sedimentary rocks, with thousands of feet of additional Cenozoic sediments on top of it. At the Tanis site, most of the Cenozoic rocks have eroded away, exposing the top of the Hell Creek Formation, where the event deposit is found.
As noted above, the state of the burrows found in the point bar just below the event deposit shows that the surface of the point bar was exposed to the atmosphere (subaerial exposure) for considerable time before being inundated with the event deposit:
Composition and structure of the Event Deposit and subjacent point bar imply an abrupt inundation of a paleosurface that was subaerially exposed for considerable time before deposition. Prolonged subaerial exposure is corroborated by colonization of the point bar by terrestrial organisms, open burrows that are filled with sediment from the overlying basal Event Deposit, pedogenic structures, and invertebrate fossils found entombed in some of the burrows.
As noted repeatedly here, this sort of exposed surface, inhabited for an extended time by terrestrial animals, could not exist in this locale where many thousands of feet of sediments lie below it, and further rock layers lie above it, if these rock layers were all laid down rapidly as part of the global Flood.
Will any of this evidence make the slightest impression on a dedicated YE creationist? Probably not – – it has been my general experience in interacting with YE creationists over the years that they simply ignore whatever facts do not fit their model. When I am able to demonstrate to a YE creationist beyond rebuttal that any particular argument of theirs cannot be sustained, they just move on to the next and the next. The busy folks at Answers in Genesis supply an unending stream of such arguments.
However, there are some devout Christians who have been taught YE creationism but who are willing and able to critically consider alternatives. Those folks can benefit from presentations which demonstrate the infeasibility of Flood geology. I know this to be the case, since articles like this played a key role in my own journey out of YE creationism.
 A variety of radioactive dating methods can be used to cross-check the date of when igneous rocks solidified. Young earth creationists attempt to discredit these methods, but their objections fail. See, for instance, Radiometric Dating A Christian Perspective (This is a classic, in-depth discussion of radioactive dating of rocks, by an evangelical scientist) and What evidence is there for the earth being billions of years old? (Brief discussion by Russell Downs at BibleQ.net of radioactive dating of rocks, answering objections raised by YE creationists.)
 For discussion of fish-amphibian intermediates see Reasonable Expectations for Transitional Fossils .
 Finding a fossil of an animal with highly derived characteristics in rock layers dated to hundreds of millions of years before those characteristics are found in any other animal fossils would be a challenge to evolution. For instance, finding a fossilized rabbit in Precambrian rocks would be problematic: a rabbit is a fully terrestrial tetrapod, with fur, mammalian jawbones and placental reproduction, but the full suite of these traits elsewhere in the fossil record only develops hundreds of millions of years later.
On the other hand, finding fossils (or living representatives) of some animal family long after they were thought to be extinct poses no challenge. This is an expected consequence of the sparseness of the fossil record. Thus, finding clear in-situ fossils of dinosaurs in rock layers well above the K-Pg boundary would not threaten evolution in the slightest. To date, though, no such confirmed fossils have been found. See https://en.wikipedia.org/wiki/Paleocene_dinosaurs. It is expected that some previously buried fossils can be eroded out of their original positions and re-deposited in more recent sedimentary layers. Geologists use physical and chemical tests to help identify such “reworked” fossils. See, for example, Staron et al. (2001). Dinosaur fossils found in Cenozoic rocks have generally been characterized as reworked Mesozoic fossils.
Side note: since birds are believed to have descended from dinosaurs, they are considered as dinosaurian survivors of the K-Pg event. To be more technically accurate, one could qualify every reference to “dinosaurs” in this essay with the adjective “non-avian”.
 See https://en.wikipedia.org/wiki/Geology_of_Montana for a summary description of Montana geology.
 By convention, the lithostratigraphic boundary between the Hell Creek and the Fort Union formations is considered to be demarcated by a dark layer of carbonaceous shale, or coal. This carbon-rich layer, presumably resulting from a swampy deposition environment, is considered to be the base of the Fort Union formation. However, this coal-type layer does not instantly appear everywhere in eastern Montana on the same day. It appears at different times in different locales, and is altogether absent in some places. See Bryan Turner, “Testing the Local Diachroneity of the Terrestrial Lithostratigraphic KPg Boundary, Northern Montana “ , Master’s Thesis, Montana State Univ. 2010 https://scholarworks.montana.edu/xmlui/bitstream/handle/1/2457/TurnerB0810.pdf?sequence=1&isAllowed=y
The K-Pg boundary layer (as marked by a fern/pollen shift, and by the Ir spike in some places) may fall at the very top of the Hell Creek ( i.e. just below the coal layer), or some distance below the top of the Hell Creek formation. That is, the chronological K-Pg boundary is not always identical with the lithostratigraphically-defined Hell Creek/Fort Union boundary.
 Bryan Turner’s thesis provides an illuminating discussion of sediment deposition in river floodplains, as applied to the Hell Creek and Fort Union sediments. https://scholarworks.montana.edu/xmlui/bitstream/handle/1/2457/TurnerB0810.pdf?sequence=1&isAllowed=y
 Just for clarity: We showed above another close-up photo of the K-Pg boundary at Mud Buttes, from a different journal article.
 R. A. DePalma., “LIFE AFTER IMPACT: A REMARKABLE MAMMAL BURROW FROM THE CHICXULUB AFTERMATH IN THE HELL CREEK FORMATION, NORTH DAKOTA” GSA Annual Meeting in Seattle, Washington, USA – 2017 Paper No. 113-16 https://gsa.confex.com/gsa/2017AM/webprogram/Paper305627.html
From the Abstract: “… The burrow, with a long, narrow entry tunnel and several simple flask-shaped chambers, penetrates through an ejecta-bearing inundation deposit that was laid down immediately after the Chicxulub impact. Sediment filling the burrow’s interior is high in palynotaxa typical for the upper Hell Creek (ie. high percentages of Aquilapollenites and Wodehouseia, low pine or fern), indicating it was excavated and abandoned very shortly after impact, predating the post-impact palynological shift that was strongly recorded in the sedimentary record. Scattered mammal bones within the burrow indicate a mid-sized (~1 to 2 kg) individual that compares favorably with the Cimolestidae…”
 For the official write-up of this Hell Creek trackway, see Lockley, M.G., Triebold, M., and Janke, P.R. 2014. Dinosaur tracks from the Hell Creek Formation (Upper Cretaceous, Maastrichtian), South Dakota. In Fossil footprints of Western North America. Edited by M.G. Lockley and S.G. Lucas. New Mexico Museum of Natural History and Science, Bulletin 62. pp. 459–468
 It is perhaps ironic that today’s fundamentalists, who claim to base their faith on the Bible alone, adhere to a physical model driven by extra-biblical trance visions reported by Adventist cult prophetess Ellen White. The Adventists trace their roots to New York State farmer William Miller’s widely-believed predictions that Christ’s Second Advent would occur on October 22, 1848. See the full story, from failed prophecy to failed science, in Exposing the Roots of Young Earth Creationism. (Today’s Seventh Day Adventism, which has many admirable features, is quite different than mid-nineteenth century Adventism.)
 A missionary to the former Soviet Union noted http://paleo.cc/paluxy/joshzorn.htm : The worst aspect of YECS [Young Earth Creation Science] teaching is that it creates a nearly insurmountable barrier between the educated world and the church… How many have chosen to give up their faith altogether rather than to accept scientific nonsense or a major reinterpretation of Scripture? How much have we dishonored our Lord by slandering scientists and their reputation? How much have we sinned against Christian brothers holding another opinion by naming them “dangerous” and “compromisers”?… We are sowing the seeds of a major crisis which will make the job of world evangelism even harder than it is already.