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1. What are fossils?
Fossils are remains or impressions of ancient organisms preserved in the rocks. There are several types of fossils, most of which are commonly grouped as either body fossils or trace fossils. Body fossils are preserved remnants of a body or some of its parts, including bones, teeth, shells, insects preserved in amber, wood, leaves, seeds, pollen, algae, etc. Molds and casts may be classified as body fossils. A mold is formed when a body dissolves away, leaving a record of its shape in the rock. A cast is formed when minerals fill in a mold and form a body-shaped fossil. Body fossils may or may not be chemically altered or not, depending on the circumstances. A frozen mammoth is an example of an unaltered body fossil. Petrified wood is an example of an altered fossil, where minerals in the ground water have replaced the woody tissue, producing a log made out of stone. Trace fossils are preserved evidence of an organism’s activities, such as burrows, nests, borings in wood or other hard substrates, footprints, coprolites (fossilized feces), etc. Molecular fossils are a relatively recent discovery. These include molecules such as fatty acids that were part of an organism and can be detected using various techniques today.
2. How are fossils formed?
Different conditions during preservation may result in different types of fossils, but rapid burial is almost always important. For example, footprints and other surface traces of activity are often quickly erased by wind or water; thus, trace fossils are usually evidence that the ground surface was buried soon after the traces formed.
Preservation of body fossils usually requires presence of hard parts, rapid burial and appropriate chemical conditions in the sediments. Hard parts, such as bones or shells, require a much longer time to decompose than soft body parts, such as internal organs. The additional time provides a greater opportunity for preservation. Rapid burial by sediments protects the potential fossil from destruction in the environment. Dead bodies are normally eliminated by scavengers within hours or days for a small animal, up to months or years for a large animal or tree. After burial, mineral-rich water may flow through the sediments and replace the tissues or fill in the pores of a buried organism with minerals. Petrified wood is a common example of this. Sometimes traces of the original tissue are still present in a fossil, but even fossil shells and bones may have experienced mineral replacement and may not be composed of original tissue. Buried organisms or parts of organisms that are mineralized are much more likely to be preserved than those that are not mineralized.
Because fossil preservation is a rare event today, it is thought that the fossil record must be very incomplete. An exception should be made for catastrophic burial, in which large numbers of organisms in an area are quickly buried and thus inaccessible to scavengers and most other destructive forces. Even catastrophic burial of a large area will yield an incomplete fossil record, because most of the soft-bodied organisms may decompose before mineralization occurs. Many examples of catastrophic burial are known.1 Examples include the fossil fish of the Green River Formation in Wyoming, the marine invertebrates of the Burgess Shale,2 and the dinosaurs in the Hilda bone bed in Alberta, Canada.3 These and other examples of extraordinary preservation provide some of the most interesting information about the fossil record.
3. How long does it take to form a fossil?
The period of time required to form a fossil varies with the type of fossil. There are some cases of instantaneous fossilization, while others take days or even months. However, fossils do not require anything like thousands or millions of years to form. The longer the time that goes by without fossilization, the less likely it is that a dead organism will be preserved.
An example of near-instantaneous fossilization is seen in the fossil fish of the Cretaceous Santana Formation in northeastern Brazil.4 Many of these fish are preserved in three dimensions. Fish normally show signs of decay in a few days or weeks after death,5 so fossilization must be accomplished rather quickly or there will be nothing left to fossilize. The exquisite state of preservation of these fish indicates they must have been fossilized in a few hours, apparently due to submergence in highly mineralized water. Similarly, experiments with crustaceans such as shrimp have shown that these creatures fall apart in a few weeks,6 even in the absence of dissolved oxygen in the environment. Well-preserved fossil shrimp must have become fossilized within that period of time.
On the other hand, durable hard parts, such as bones and shells, can persist in the environment for many years, so their preservation can be either rapid or slow. Bones left on the surface are usually destroyed by scavengers and decomposers in a few days or weeks, while shells may last for hundreds of years if conditions are favorable.7 If bones or shells are disarticulated, this may indicate a longer passage of time between death and preservation. Because of their durability, bones, shells and teeth are among the most common types of fossils.
4. What information do we learn from fossils?
By examining the anatomy of a fossil animal, we may be able to infer its size, shape, method of locomotion, and what kind of diet it had while alive. We may also learn a great deal about their behavior and their paleoecological relationships. The nature of the surrounding sediments may reveal whether the environment was a river, a lake, a beach, shallow or deep marine water, etc. For example, a fine-grained shale with diverse kinds of fossils of marine bottom-dwelling creatures would indicate a seafloor habitat, while a coarse-grained deposit with terrestrial vertebrates would likely be interpreted as a river deposit. The quality of preservation of the fossil may indicate whether the fossil was buried rapidly, or whether scavengers had started to attack the body. By comparing fossils with living organisms, we know that many kinds of organisms have become extinct. By observing patterns and trends through the fossil record, we may infer something about the history of the rocks.
Fossils show us that organisms in the past were complex and fascinating, as they are today, but they typically tell us little about the color of organisms, the sounds they may have made or many other details we may observe in living organisms. When we see colorful animations of dinosaurs bellowing or hissing, we should remember that such reconstructions are based on educated guesses rather than direct observation.
5. Why is there a specific sequence of fossils in the geologic layers?
The earth’s sediments have been deposited by wind and water, and these processes normally produce layers of sediment, which may bury plants and animals as the sediments accumulate. It is not surprising to find many layers of fossils in the rock record. However, the different kinds of fossils are not found randomly distributed throughout the rock layers, but are sorted into a sequence that seems quite consistent in different localities across the globe. The many different kinds of fossils occurring in different sedimentary layers form what is called the fossil record.
Different worldviews provide different explanations for the presence of order in the fossil record and the specific sequence of fossils that is observed. One proposed explanation for the fossil sequence is that much of it was caused by the Genesis flood. In a global flood, the lowest surfaces would be expected to be filled first. Since the lowest surfaces are the ocean floors, we would expect to find marine fossils before terrestrial fossils. Moreover, we would expect that species living in the first habitats to be destroyed would be least likely to have survived the flood and still be living. As the ocean floors were covered with sediment, we might expect to find fossils of species from low-lying areas, followed by fossils of species from higher elevations. This theory was first proposed by Harold W Clark8 and is called the Ecological Zonation Theory.
Several predictions of Ecological Zonation Theory are fulfilled in the fossil record. For example, the lowest layers with abundant fossils have representatives of most of the body plans, or phyla, of living organisms, as well as many types that are now extinct. The abrupt appearance of diverse types of marine animals at the bottom of the fossil layers is famously known as the Cambrian Explosion. Also, fossils of terrestrial organisms appear in a sequence that correlates reasonably well with increasing terrestriality. In general, the types of fossils that appear in the lower layers are less likely to be found living than those in the higher layers. These general patterns are consistent with Ecological Zonation Theory. However, there has been very little research on the theory,9 and much more research is needed.
Some of the inadequacies of Darwinian theory in attempting to explain the fossil record are discussed below.
6. Does the fossil record show a sequence of evolutionary change?
The fossil sequence shows us the sequence in which various types of organisms were buried, but it does not tell us how the fossilized organisms originated. Materialistic Darwinism and theologies such as theistic evolution attempt to explain the fossil sequence as a record of evolutionary change. Evolutionary theories explain some features of the fossil record, such as the sequence of first appearances of the vertebrate classes, and the gradually changing composition of fossil assemblages in some parts of the geologic column. On the other hand, it has been notably unsuccessful in explaining other features of the fossil sequence, such as the abrupt appearance of diverse animal forms in the Cambrian layers, a feature known as the “Cambrian Explosion.” The first fossils in the basal Cambrian layers show high complexity and diversity, something not predicted by Darwinian theory. The pattern of abrupt appearance of fully formed and diverse species within groups is repeated on a less spectacular scale in other organisms such as birds and flowering plants.
Gradual evolution also fails to explain adequately the shortage of potential transitional links between the different types of organisms throughout the column. The majority, if not all, animal and plant forms appear abruptly in the fossil record without known ancestors or intermediate forms. For example, bats, ants, dragonflies, cockroaches and many others appear in the fossil record without any apparent ancestors, and look much like their modern counterparts. This pattern of abrupt appearance does not fit models that invoke gradual evolution, and may fit better in a global catastrophe model. Moreover, Darwinian theory fails to explain how changes in genetic information can produce new types of organs and body plans. Because of these failures, Darwinian theory is not a satisfactory explanation for the fossil sequence.
7. Which fossils were buried by the Flood?
We do not have enough information to give definitive answers to this question. It appears that the geological activity associated with the Flood did not abruptly stop, but continued after the ark was opened, and still continues today. There does not appear to be any global feature that clearly distinguishes fossils buried during the flood from those buried after the ark rested on dry ground. However, there are some interesting patterns that may provide some clues.
Some features of the geological record point to conditions quite different from the present. For example, much of the present continental surface is covered with sediments containing marine fossils. This means the area that is now continental may once have been covered by the sea. Another interesting feature is the presence of sedimentary layers that cover very wide areas – much larger than anything we see today. For example, a rock formation known as the Shinarump Conglomerate10 covers a large area in the southwestern United States. It is called the Shinarump in the region of southern Nevada, southern Utah, northern Arizona and western New Mexico. The formation goes by different names in Texas, Wyoming and Idaho. Such widespread continental deposits are unusual. The present land surface is divided into basins, and each basin collects sediments separately. The geographic extent of the layers in any basin is limited by the size of the basin. The geographic extent of geologic layers in the rock record (and by inference, basins) is often strikingly large compared to present conditions.11
8. Are there indications of global catastrophe in the fossil record?
The fossil record contains compelling evidence of global catastrophic processes, although they are generally interpreted within the standard geologic framework as occurring in discrete events separated by long periods of time. Patterns in the fossil record known as “mass extinctions” provide an interesting yet enigmatic example. Some (but not all) of the kinds of fossils found in one geological layer are different from those found in another layer, which means there is a change in the fossil composition as one moves through the geologic column. In the Darwinian, long-age model, this is interpreted to reflect changing conditions over long periods of time
The turnover in fossil species is especially abrupt at certain points in the geologic column. The dinosaurs provide a familiar example, in which the uppermost Cretaceous sediments contain numerous types of fossil dinosaurs, while the overlying Paleogene sediments contain none.12 The explanation for this abrupt change at what is commonly known as the “KT Boundary13” is that dinosaurs somehow became extinct globally at the time when the last Cretaceous sediments were deposited. The cause of the extinction is widely held to be a catastrophic extraterrestrial impact in the Yucatan Peninsula of Mexico, perhaps aided by an enormous outflow of lava in India (the Deccan Traps). However, there are some problems with the scenario, and it is currently debated vigorously. Another example is the extinction of mammoths, mastodons and other large terrestrial mammals. Scientists disagree on whether they went extinct because of the Ice Age, because of extensive killing by humans, or by both. Several other large mass extinctions have been identified, each of which is thought to be associated with some catastrophic global process, although the nature of the postulated processes has not been determined. Mass extinctions, presumably associated with global disaster, are an important but poorly understood feature of the fossil record.
9. What does the fossil record tell us about earth history?
The fossil record provides good evidence for both intelligent design and catastrophe in earth history. Intelligent design is seen in the complexity and specialization present in the fossil organisms throughout the fossil record. The only known sufficient cause for such features is the activity of an intelligent designer. Catastrophe is seen throughout the fossil record in the form of “mass extinctions” and geological features such as impact craters, flood basalts, tsunamis, storm deposits, etc. While the time over which these processes occurred may be controversial, no one need miss the clear evidence of design and catastrophe in the fossil record.
10. What unsolved questions about fossils are of the greatest interest?
How did the fossils become arranged in the particular sequence in which we find them? What do the fossils tell us about the biblical Flood? Why do some organisms living today appear to go extinct in the fossil record? What geologic layers might have been deposited at the start and end of the Genesis flood? Why do some organisms, such as the brachiopod Lingula, appear throughout the fossil record while others appear or disappear?