~Fossils are the prerved remains or traces of animals, plants, and other organisms from the remote past. The totality of fossils, both discovered and undiscovered, and their placement in fossiliferous rock formations and dimentary layers is known as the fossil record. 发现和未被发现的,他们放置在含有化石的岩层和沉积一层被称为化石记录。~The study of fossils across geological time, how they were formed, and the evolutionary relationships between taxa are some of the most important functions of the science of paleontology. Such a prerved specimen is called a "fossil" if it is older than some minimum age, most often the arbitrary date of 10,000 years. Hence, fossils range in age from the youngest at the start of the Holocene Epoch to the oldest from the Archaean Eon, up to 3.48 billion years old. The obrvation that certain fossils were associated with certain rock strata led early geologists to recognize a geological timescale in the 19th century. The development of radiometric dating techniques in the early 20th century allowed geologists to determine the numerical or "absolute" age of the various strata and thereby the included fossils.
````Like extant organisms, fossils vary in size from microscopic, even single bacterial cells o
ne micrometer in diameter, to gigantic, such as dinosaurs and trees many meters long and weighing many tons. A fossil normally prerves only a portion of the decead organism, usually that portion that was partially mineralized during life, such as the bones and teeth of vertebrates, or the chitinous or calcareous exoskeletons of invertebrates. Fossils may also consist of the marks left behind by the organism while it was alive, such as animal tracks or feces. The types of fossil are called trace fossils , as oppod to body fossils. Finally, past life leaves some markers that cannot be en but can be detected in the form of biochemical signals; the are known as chemofossils or biomarkers
1Permineralization
Permineralization is a process of fossilization that occurs when an organism is buried. The empty spaces within an organism become filled with mineral-rich groundwater是石化的过程,发生在生物体被埋。空的空间在一个生物体变得满是矿产资源丰富的地下水. Minerals precipitate from the groundwater, occupying the empty spaces. 从地下水矿物质
沉淀,占据空的空间。This process can occur in very small spaces, such as within the cell wall of a plant cell. Small scale permineralization can produce very detailed fossils. 这个过程可以发生在非常小的空间,如在植物细胞的细胞壁。小规模石化可以产生非常详细的化石。For permineralization to occur, the organism must become covered by diment soon after death or soon after the initial decay process石化发生,机体必须成为被沉积物覆盖后不久死亡或不久之后最初的衰变过程。The degree to which the remains are decayed when covered determines the later details of the fossil. Some fossils consist only of skeletal remains or teeth; other fossils contain traces of skin, feathers or even soft tissues. This is a form of diagenesis. 覆盖时的遗体腐烂的程度决定了后来化石的细节。一些化石由只剩下的骨骼或牙齿;其他化石含有皮肤,羽毛甚至软组织。这是成岩作用的一种形式。
2Casts and molds石膏模型
In some cas the original remains of the organism completely dissolve or are otherwi destroyed. The remaining organism-shaped hole in the rock is called an external mold. 在
某些情况下,原始的生物完全溶解或者其他破坏。其余具有生物体形状的洞岩被称为外部模具。 If this hole is later filled with other minerals, it is a cast. An endocast or internal mold is formed when diments or minerals fill the internal cavity of an organism, such as the inside of a bivalve or snail or the hollow of a skull. 如在双壳类动物或蜗牛或空心的头骨。
3Authigenic mineralisation自生矿化
This is a special form of cast and mold formation. If the chemistry is right, the organism can act as a nucleus for the precipitation of minerals such as siderite, resulting in a nodule forming around it. If this happens rapidly before significant decay to the organic tissue, very fine three-dimensional morphological detail can be prerved. 这是一种特殊形式的演员和模具的形成。如果化学是正确的,有机体可以作为核菱铁矿等矿物的沉淀,导致周围结节形成。如果发生这种情况之前迅速严重腐烂的有机组织,非常好的三维形态细节可以被保留下来
4Replacement and recrystallization替换和再结晶[edit]
Replacement occurs when the shell, bone or other tissue is replaced with another mineral更换时外壳,骨或其他组织被替换为另一种矿物. In some cas mineral replacement of the original shell occurs so gradually and at such fine scales that microstructural features are prerved despite the total loss of original material. 在某些情况下矿物替代原来的外壳发生逐渐在这样的细鳞片,显微结构的功能是保存尽管原始材料的总损失 A shell is said to be recrystallized when the original skeletal compounds are still prent but in a different crystal form, as from aragonite to calcite. shell是再结晶时原始骨架化合物仍然存在,但在不同的晶体形式,方解石和霰石。
5Carbon films碳膜[edit]
Carbonaceous films are thin coatings which consist predominantly of the chemical element carbon. The soft tissues of organisms are made largely of organic carbon compounds and during diagenesis under reducing conditions only a thin film of carbon residue is left which forms a silhouette of the original organism.
