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A lot of people, who are fond of paleontology, history, biology, archaeology, and just those who are keen on exploring antiquities, at least once in their lives have seen a dinosaur skeleton. Around the world, in many paleontological museums you can find fossils, Tyrannosaurus skeleton, mammoth tusks, saber-toothed tiger fangs, Megalodon teeth, Triceratops bones, and much more. But have you ever thought about the fact that what we see in museums is not bones at all? More than that: in the whole exhibition, no matter how hard you try, but you will not find a single bone. But, you may have a legitimate question, if it's not bones, then what?
Fossils, petrifactions, or phossilias - variations of the names to call them can be different - are the products of a long physical and chemical process. Fossils are usually mineralized remains or prints of animals and plants preserved in the soil, stones, hardened resins. It is also known as fossilized traces, such as the feet of an organism on soft sand, clay, or mud. Strictly speaking, what were bones millions of years ago collapsed, leaving behind bone residue. Under the influence of chemical processes, this bone residue became a bone-shaped stone over the years.
In fact, the process of fossil formation is quite mysterious. First of all, because no scientist has ever been able to reproduce this process in a laboratory. The following explanation is usually given in geology textbooks. The process of mineralization occurs as salts gradually accumulate in tissues. Organic matter molecules are replaced by silicon salts as they are washed out. Examples are usually the leaf and feather prints of plants and birds feathers formed when objects are pressed into soft mud, which is then, hardened, turned to stone. Obviously, the animals, whose corpses were found completely preserved in the ice blocks, died suddenly. For a better understanding of the fossilization process, let's look at examples. The most logical explanation would be that fossils are made up of dead plants and animals that were not instantly eaten by raptors or bacteria, but soon after their death was covered with silt, sand, clay, and ash, which excluded access to oxygen. In the course of formation from rock sediments, under the influence of mineral solutions organic matter was decomposed and replaced minerals - most often calcite, pyrite, opal, chalcedony. And thanks to the gradual progress of the substitution process, the external shape and elements of the remains' structure were preserved. Usually only hard parts of organisms like bones, teeth, chitin shells, the sinks. The soft tissues decompose too quickly and don't have time to be replaced by a mineral substance. Plants are usually completely destroyed during phossification, leaving what is known as prints and cores. Also plant tissues can be replaced by mineral compounds, most commonly silica, with carbonate and pyrite. Such total or partial substitution of trunks of plants while maintaining the internal structure is called petrification.
There are many reasons for the formation of fossils. Let's consider the most significant of them.
Most often it happens in a desert climate. Tissues such as skin, hair, and even muscles are most often preserved when dry. Some of the remains of terrestrial vertebrates have been preserved in this way - when they are dried. Thanks to this, we have received the rarest samples of fossilized dinosaur skin prints.
Freezing in permafrost can preserve blood and internal organs for tens of thousands of years. This is how mammoths and other glacial-era animals such as woolly rhinos, horses, wolverines, and bison found in Siberia and Alaska have been preserved. Sometimes they also find human remains, such as the "Ice Man" from Tyrol. They cannot, however, be considered petrified forever as permafrost will not always exist, but they represent an invaluable source of information about the conditions that existed in the Ice Age.
Amber is one of the most famous natural preservation media. Many different creatures are found in amber - from fly flies to bird feathers and parasitic insects. As amber is considered an organic rock in geology, it means that burial in amber can be considered a real fossil.
The oxygen-free environment is an ideal environment for the formation of fossils, as microbes and microorganisms that can contribute to the complete decomposition of the organism, in such an environment simply will not survive. Under these conditions, minerals such as calcium phosphate and ferrous pyrites are formed. They cover the soft organs of the body, such as muscle fibers, skin, feathers, intestines, and even the delicate tissues of the gills, and accurately reproduce their shape.
Remains of ancient animals and plants, which were excavated, are localized in thickness, sedimentary rocks (limestones, clays, sands, and sandstones) formed by in the geological periods in which these organisms lived. The exit points sediments on the surface can be natural (river valleys, cliffs, ravines, mountain ridges, etc.) and artificial (quarries, mines, road excavations) of origin. As a rule, in places of extensive exits to the surface of sedimentary rock fossil finds are not uncommon. However, the locations of large clusters of interesting and unique fossils are rare. There are known in the world only a few dozen areas with major locations fossils, which is where most samples come from.
Only a few dozen areas with large fossil locations are known in the world, from which most samples come:
After finding a fossil, one of the most important questions for scientists is how to determine the age of a fossil? How many thousands or millions of years ago did the organism that was found lives? How is it possible to determine whether the dinosaur lived in the Triassic, Jurassic, or Cretaceous periods? In geology there are notions of absolute and relative age. Absolute age is determined by measuring the content in the mountains. rocks of radioactive isotopes and products of their decay, such as uranium and lead. Uranus turns to lead very slowly - its period half-life exceeds 1 billion years. Knowing the proportions in the rock of uranium and lead, as well as uranium's half-life (for each isotope known) it is possible to determine the age of rocks and the rocks contained therein fossils. The relative age of rocks and fossils is determined at the presence in this layer of other fossils that have lived a short stretch of a time for which an absolute age had previously been set. If, For example, fossilized fish remains were found in the same layer with ammonite, which is already known to exist only in the time of the Upper Cretaceous period, then the remains of the fish will be Upper Cretaceous.