In the long geological age, countless creatures lived on the earth, and many of their dead bodies or traces left by life were buried by the sediment at that time. In the following years, the organic matter in these biological remains was completely decomposed, and the hard parts, such as shells, bones, branches and leaves, together with the surrounding sediments, were petrified into stones, but their original forms and structures (even some subtle internal structures) still existed; Similarly, the traces left by those creatures when they are alive can be preserved in this way. We call these fossils biological remains and remains fossils. By studying fossils, scientists can gradually understand the form, structure and category of organisms in the distant past, infer the origin, evolution and development process of organisms for hundreds of millions of years, and restore the earth's ecological environment at various stages in the long geological history.
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Fossil fossils
The remains of ancient animals or plants preserved in crustal rocks or evidence indicating the existence of remains are called fossils.
Simply put, fossils are stones made from the remains or remains of creatures living in the distant past. In the long geological era, countless creatures have lived on the earth. The remains or lives of these creatures after death are all traces left behind, and many of them were buried by the sediment at that time. In the following years, the organic matter in these biological remains was completely decomposed, and the hard parts, such as shells, bones, branches and leaves, together with the surrounding sediments, were petrified into stones, but their original forms and structures (even some subtle internal structures) still existed; Similarly, the traces left by those creatures when they are alive can be preserved in this way. We call these fossils biological remains and remains fossils.
Etymology:
The word Fossil comes from the Latin word "fossilis", which means to dig out. Most fossils are hard parts of prehistoric creatures that can be preserved. These creatures live in fossil collection areas.
Fossils in history
In the early recorded human history, some Greek scholars were very confused about the existence of fish and marine shells in deserts and mountains. In 450 BC, Herodotus noticed the Egyptian desert and correctly thought that the Mediterranean Sea had flooded that area.
In 400 BC, Aristotle announced that fossils were formed by organic matter, but the burial of fossils in rocks was the result of mysterious plastic forces inside the earth. One of his students, Theophrastus (about 350 BC), also suggested that fossils represent some life forms, but he thought that fossils developed from seeds and eggs buried in rocks. Strappo (about 63 BC to 20 AD) noticed the existence of marine fossils above sea level, and correctly concluded that the rocks containing such fossils had been greatly uplifted.
In the dark ages of the Middle Ages, people had various interpretations of fossils. People either interpret them as strange phenomena in nature, or interpret them as special creations and designs of the devil to confuse people. For hundreds of years, these superstitions and the opposition of religious authorities have hindered fossil research. /kloc-At the beginning of the 5th century, the true origin of fossils was generally accepted. People understand that fossils are the remains of prehistoric creatures, but they are still considered to be the remains of the great flood recorded in the Christian Bible. The debate between scientists and theologians lasted for about 300 years.
During the Renaissance, several early natural scientists, the famous Leonardo da Vinci, talked about fossils. He insisted that the flood could not be responsible for all fossils, nor could it explain why fossils appeared in the mountains. Scientists firmly believe that fossils are indisputable evidence of ancient life, and the ocean once covered Italy. He believes that the remains of ancient animals were buried deep in the sea floor, and at some point later, the sea floor rose to form the Italian peninsula. 1at the end of the 8th century1at the beginning of the 9th century, the study of fossils laid a solid foundation and formed a science. Since then, fossils have become more and more important to geologists. Fossils are mainly found in marine sedimentary rocks. Marine sedimentary rocks are formed when sediments in seawater, such as calcareous ooze, sand and shell layers, are compacted and gelled into rocks. Only rare fossils occur in volcanic rocks and metamorphic rocks. Volcanic rocks used to be molten and there was no life in them. Great changes have taken place in metamorphic rocks, making the fossils in the original rocks generally disappear. However, even in sedimentary rocks, the preserved records are only a small part of prehistoric animals and plants. If we consider the harsh conditions required in the process of fossil formation, it is not difficult to understand why only a small number of prehistoric animals and plants are preserved in sedimentary rocks.
Formation conditions:
Although whether an organism can form fossils depends on many factors, three factors are basic:
(1) Organic matter must have hard parts, such as shells, bones, teeth or woody tissues. However, even very fragile organisms, such as insects or jellyfish, can become fossils under very favorable conditions.
(2) living things must avoid being destroyed immediately after death. If an organism's body is partially crushed, decayed or severely weathered, it may change or cancel the possibility of this organism becoming a fossil.
(3) living things must be quickly buried by things that can hinder decomposition. The type of this buried material usually depends on the living environment of organisms. The remains of marine animals can usually become fossils, because marine animals sink to the bottom of the sea after death and are covered with mud. In later geological periods, mud became shale or limestone. Fine-grained sediments are not easy to destroy biological remains. In some fine-grained sedimentary rocks of Jurassic in Germany, some fragile organisms such as birds, insects and jellyfish are well preserved.
Other circumstances:
It has been known that volcanic ash from nearby volcanoes once covered the whole forest, and sometimes standing trees can be seen in forest fossils, which have been preserved in a good attitude. Quicksand and asphalt can usually bury animals quickly. The function of tar pitch is like a trap to catch wild animals, and it is also like a preservative to prevent the hard parts of animals from decomposing. Rancho in Los Angeles? Pull? Rancho laBrea asphalt lake in brea is famous for finding many skeletal fossils in it, including wild boar with sharp teeth, giant land sloths and other extinct animals. The remains of some animals that survived the ice age were frozen in ice or frozen soil. Obviously, some frozen animals can be preserved.
Although many unknown creatures have appeared on the earth, only a few have left fossils. However, even if the conditions for turning organisms into fossils are met, there are still other reasons why some fossils have never been discovered. For example, many fossils are destroyed by ground erosion, or its hard parts are decomposed by groundwater. Some fossils may be preserved in rocks, but because rocks have undergone strong physical changes, such as folding, breaking or melting, this change can turn marine limestone containing fossils into marble, and any biological traces that originally existed in limestone will disappear completely or almost completely. There are still many fossils in sedimentary rocks that cannot be obtained for research, and some rocks containing fossils are well exposed on the earth's surface, but they have not been studied in geology. Another very common problem is that the situation of organisms may not be fully displayed because the remains of organisms have become fragments or poorly preserved.
In addition, the longer we go back to the past, the longer the interval between losing fossil records. The older the rock is, the more chances it will be damaged, and the more unrecognizable the fossil will be. In addition, since older creatures are different from today's creatures, it is difficult to classify them, which makes the problem more complicated. However, despite this, a large number of preserved biological fossils still provide a good record for us to understand the past.
Animals and plants can become fossils in many different ways, but which way usually depends on:
(1) The original composition of living things
(2) the place where it lives
(3) the force that affects the residue after death.
Most paleontologists believe that there are four forms of preservation of biological remains, each of which depends on the composition of biological remains or the changes they have undergone.
The original soft part of a living thing can only be preserved if it is buried in a medium that can prevent its soft part from decomposing. This medium includes frozen soil or ice, oil-rich soil and amber. When a creature becomes a mummy under very dry conditions, it can still retain the original soft part of its body. This situation generally only occurs in arid areas or desert areas, and the remains will not be eaten by wild animals.
Perhaps the most famous animal mollusk fossils are preserved in Alaska and Siberia. A large number of frozen mammoth remains-an extinct elephant-were found in the tundra of these two areas. Some of these behemoths have been buried for 25,000 years. When the frozen soil melts, the remains of mammoths are exposed. There are also some bodies that are poorly preserved. When they are exposed, their meat is eaten by dogs and their ivory is resold by ivory dealers. Mammoth fur is now on display in many museums, some of which preserve mammoth meat or muscle in ethanol.
Soft parts of biological bodies are also found in oily soil in eastern Poland, where the nose horns, front legs and part of the skin of extinct rhinos are well preserved. Natural ground sloth mummies were found in caves and craters in New Mexico and Arizona. The extremely dry desert climate here can dehydrate all the soft tissues of animals before decay, and can preserve some skin, hair, tendons, claws and so on.
A more interesting and unusual way for organisms to become fossils is to keep them in amber. Ancient insects can be captured by mucus secreted by some conifers. When turpentine hardens and further turns into amber, insects stay inside. Some insects and spiders are so well preserved that they can even study their fine hairs and muscle tissues under a microscope.
Although the preservation of biological soft tissue has formed some interesting and amazing fossils, the fossils formed in this way are rare. Paleontologists often study fossils preserved in rocks.
Hard tissues on organisms can also be preserved. Almost all plants and animals have some hard parts, such as clams, oysters or snails; Teeth and bones of vertebrates; Crab shells and woody tissues of plants can become fossils. Because the hard parts of living things are made of substances that can resist weathering and chemical action, such fossils are widely distributed. The shells of invertebrates such as clams, snails and corals are made of calcite (calcium carbonate), and many of them have survived with little or no physical changes. The bones and teeth of vertebrates and the exoskeletons of many invertebrates contain calcium phosphate. Because this compound is very resistant to weathering, many substances composed of phosphate can also be preserved, such as a well-preserved fish tooth. Bones made of silicon dioxide also have this property. The siliceous part of microfossils and some sponges become fossils through silicification. Other organisms have chitin (a substance similar to nails), and the chitin exoskeleton of arthropods and other organisms can become fossils. Because of its chemical composition and burial method, this substance is preserved in the form of carbon film. Carbonization (or distillation) occurs in the process of slow decay after biological burial. In the process of decomposition, organic matter gradually loses its gas and liquid components, leaving only carbonaceous films. This carbonization is the same as the formation of coal. A large number of carbonized plant fossils can be seen in many coal seams.
In many places, plants, fish and invertebrates have preserved their fossils in this way.
Some carbon films accurately record the finest structures of these creatures.
Fossils can also be preserved through mineralization and fossilization. When mineralized groundwater deposits minerals in the space where the biological hard part is located, the biological hard part becomes harder and more resistant to weathering. Common minerals are calcite, silica and various iron compounds. The so-called replacement or mineralization is the process that the hard part of the organism is dissolved by groundwater and other substances are precipitated in the vacated position. The original structure of some displaced fossils was destroyed by displaced minerals.
Not only the remains of animals and plants can form fossils, but also the evidence or traces that show that they once existed can form fossils. Trace fossils can provide a lot of information about this biological feature. Shells, bones, leaves and other parts of many creatures can be preserved in the form of male and female molds. If the shell is pressed into the seabed before the sediment hardens and rocks, its external features will be impressed (female die). If female die is later filled with another substance, a male mold is formed. The male mold can show the original external features of the shell. The vulva model shows the external characteristics of the hard part of the organism, and the internal female die shows the internal characteristics of the hard part of the organism.
Some animals leave evidence of their existence in the form of marks, prints, footprints, holes and holes.
For example, footprints can not only indicate the species of animals, but also provide environmental information. The dinosaur footprint fossils not only reveal the size and shape of its feet, but also provide clues about its length and weight. Footprint rocks can also help determine the environmental conditions for dinosaurs to survive. The most famous dinosaur footprint fossil in the world was found in the limestone of the Palus river bed near Ross Town, Somerville County, Texas, USA in the late Cretaceous, about 1. 1 billion years ago. Large limestone slabs with dinosaur footprints have been transported to museums around the world as silent evidence of this giant reptile. Invertebrates also leave traces. They can be found on the surface of many sandstone and limestone deposits. Traces of invertebrates range from simple traces to caves of crabs and other reptiles.
These footprints provide evidence for the way these creatures move and their living environment. A cave is a tubular or circular hole made of wood, stone and other substances that can make holes for animals to hide and feed. It may be preserved if it is filled with fine substances later. Occasionally, the remains of animals that escaped from caves can be found in the sediments filled with caves. Worms, arthropods, mollusks and other animals can stay in caves on the soft seabed. Some mollusks, such as shipwrecks, a wood-drilling clam, and Litho-domus, a diamond-drilling clam, can often find their cave fossils and borehole fossils. Among the oldest known fossils, there is a tubular structure, which is considered as a worm's cave. This tubular structure exists in many of the oldest sandstones.
Boreholes are holes that some animals dig for food, attachment and hiding. Boreholes often appear in fossil shells, wood and other biological fossils. Borehole is also a kind of fossil. Endophagous animals such as drilling snails can drill holes in the shells of other animals and eat their soft parts. Many ancient mollusks can see neat holes in their shells, which look like drilling snails.
Fossils are useful for tracing the development and evolution of animals and plants, because fossils in older rocks are usually primitive and simple, while fossils of similar species in newer rocks are complex and advanced.
Some fossils are valuable as indicators of the environment. For example, reef-building corals always seem to live in conditions similar to today. Therefore, if geologists find coral reef fossils, where corals were originally buried, it is reasonable to think that these rocks containing corals were formed in a warm and quite shallow ocean. This makes it possible to outline the location and scope of the ocean in prehistoric times. The existence of coral reef fossils can also indicate the depth, temperature, bottom condition and salinity of ancient water bodies.
The more important use of fossils is for comparison-to determine the close relationship between several rock layers. By comparing or comparing the characteristic fossils contained in various strata, geologists can determine the distribution of some geological structures in a particular area. Some fossils exist for a short time in geological history, but they are widely distributed in geography. This kind of fossil is called indicator fossil. Because this kind of fossil is usually born only with rocks of a certain era, it is particularly useful in comparison.
Microfossils are particularly useful as indicator fossils for petroleum geologists. Micro-paleontologists (scholars who study micro-paleontology) separate tiny fossils by cleaning the cores obtained by drilling holes, and then study them under the microscope. The data obtained by studying these tiny paleontological remains are very valuable for judging the age of underground rock formations and the possibility of oil storage. The importance of microfossils to the world oil fields can be seen from the naming of some oil-bearing strata by some key foraminifera. Other microfossils, such as ostracods, spores and pollen, are also used to identify underground rock formations in many other parts of the world.
Although plant fossils are very useful for indicating climate, they are not very reliable for stratigraphic correlation. Plant fossils provide a lot of information about the evolution of plants in the whole geological era.
Fossil classification
Fossils in strata can be roughly divided into four categories according to their preservation characteristics: solid fossils, die-casting fossils, trace fossils and chemical fossils.
1. Solid fossils: refer to fossils in which almost all or part of paleontological remains have been preserved. Protozoa can avoid air oxidation and bacterial corrosion under particularly suitable conditions, and their hardware and software can be completely preserved without major changes. For example, the mammoth (found in the frozen soil of Siberia during the Quaternary Glaciation 190 1 year ago, not only the bones are intact, but also the skin, hair, flesh and blood and even the food in the stomach are well preserved).
2. Die-cast fossils: marks or recasts left by biological remains in strata or surrounding rocks. One kind is imprint, that is, the imprint left by biological remains after they fall to the bottom of the water. The remains are often destroyed, but this imprint reflects the main characteristics of organisms. Creatures without hard shells can also preserve their soft impressions under certain geological conditions, the most common being the impressions of plant leaves. The second category is impression fossils, including external model and internal model. The external model is the trace of the hard part of the relic (such as shell) printed on the surrounding rock, which can reflect the original biological appearance and structure; Internal model refers to the traces of the internal contour structure of shells printed on surrounding rocks, which can reflect the internal morphology and structural characteristics of biological hardware. For example, when a shell is buried in sandstone, its internal cavity is also filled with sediments. When the sediment solidifies into rock and the shell is dissolved by groundwater, the outer mold of the shell remains on the contact surface between the surrounding rock and the shell surface, and the inner mold remains on the contact surface between the surrounding rock and the shell surface. The third type is called core, and the sediment filler in the shell mentioned above is called core. Its surface is an internal model. The shape and size of the core is equal to the size of the internal space of the shell, and it is an entity that reflects the internal structure of the shell. If there is no sediment in the shell, when the shell dissolves, it will leave a space with the same shape and size as the shell. If this space is filled again, it will form an entity with the same shape, equal size and uniform composition as the original shell, which is called the outer core. The shape of the outer core surface is the same as that of the original shell, and it is printed by the outer mold, but its interior is solid, which can not reflect the internal characteristics of the shell. The fourth is casting mold. When the shell is buried in the sediment and the outer mold and the inner core have been formed, the shell is completely dissolved and filled with another mineral, so that the filling keeps the original shape and size of the shell, just like the casting process, thus forming the casting mold. Its surface is the same as the original shell, and there is a core inside them, but the fine structure of the shell itself has not been preserved.
Generally speaking, the concave and convex patterns of the outer mold and the inner mold are just the opposite of the original. The external shapes of the outer core and the mold are completely consistent with the original, but the internal structure of the original is destroyed and disappeared, and its material composition is also different from the original. As for the difference between the outer core and the mold, the former has no inner core, while the latter also contains an inner core.
3. Trace fossils: refers to the traces and remains of paleontological life activities preserved in rock formations. The most important trace fossils are footprints. In addition, there are traces of crawling, caves, drilling holes of arthropods and hidden caves formed by tongue-shaped shellfish living in coastal areas, which can form trace fossils. In terms of trace fossils, it often refers to animal excrement or eggs (egg fossils); The dung balls and particles of various animals can form dung fossils. Dinosaur eggs in Cretaceous strata in China are world-famous. Dinosaur eggs were found in Laiyang, Shandong Province and Nanxiong, Guangdong Province in the past.
4. Chemical fossils: Although the remains of some ancient creatures have been destroyed and not preserved, various organic substances such as amino acids and fatty acids formed by the decomposition of biological organic components can still remain in the rock formations. This fossil is invisible, but it has a certain chemical and molecular structure, which is enough to prove the existence of creatures in the past. With the progress of modern chemical research and the improvement of science and technology, the organic molecules of ancient organisms (referring to amino acids, etc. ) can be separated from rock strata for identification and research, and a new discipline-paleontology has emerged.
5. Special fossils:
Amber-a large amount of resin secreted by ancient plants, with strong viscosity and high concentration, is sticky when insects or other creatures fly on it. After sticking, the resin continues to flow out, and the insect body may be completely wrapped by resin. In this case, the outside air can't penetrate, and the whole creature is preserved without any obvious changes. This is amber.
The keel of mammoth Chinese medicine shop, which is used as the keel of Chinese medicine, is actually mainly the bones and dental calculus of many vertebrates that have not been completely fossilized in the late Cenozoic, mostly Pliocene and Pleistocene mammals, such as rhinoceros and three-toed horse. , deer, deer and elephants. As for the five-flower keel or five-flower dragon tooth, the color is not monotonous white, gray or yellow-white, but red-brown or blue-gray patterns are mixed between yellow and white. This is the elephant's front teeth.