This kind of fossil is called the "time pointer" of the rock layer

During its long geological development and evolution, the Earth has supported and multiplied a large number of ancient organisms, including animals, plants, and microorganisms. Most of them have disappeared in the long river of history, and only a small part of them have become fossils and preserved in the strata, becoming an important basis for us to divide geological ages, study the origin and evolution of life, study paleogeography and paleoclimate, and analyze crustal movement.

The origin of the standard fossil

The evolution of ancient organisms is progressive, staged and irreversible, so it is of great significance in the comparison of strata and the determination of stratum age. Some fossils can determine the stratum age more accurately and are called time pointers of rock strata by geologists. They are standard fossils. So what are the characteristics of standard fossils? 1. Short span of time, short span of time means stable strata; 2. Significant features, which are easy to identify; 3. Large number, which makes it easy to find in strata; 4. Wide geographical distribution, which makes it easy to compare and has practical significance.

Age limit of standard fossils

Standard fossils are distributed in strata of different ages since about 540 million years. Typical standard fossils of each age are as follows (see the figure below): Cambrian (equivalent to the geological period of 541.0Ma to 485.4Ma): Ledleyi, Bat, Deinonychus, Butterfly; Ordovician (equivalent to the geological period of 485.4Ma to 443.8Ma): Chinese Orthomorpha, Chinese Hornstone, Antigraptolite, Forkygraptolite; Silurian (equivalent to the geological period of 443.8Ma to 419.2): Slipper Coral, Hexagonal Coral, Owl Head Shell, Bow Stone Swallow; Carboniferous (equivalent to the geological period of 358.9Ma to 298 .9Ma geological period): False Staffel dragonfly, wheat dragonfly, small spindle dragonfly, large long-bodied clam, split-beaked stone swallow, false Ula coral, Yuan coral; Permian (equivalent to 298.9Ma ~ 252.17Ma geological period): New Mis dragonfly, false Shivager dragonfly, early plate coral; Carboniferous-Permian ancient plants: Lepidoptera, Amur wood, comb fern, vein fern, wheel leaf, large feather fern, Corda, single web fern; Triassic (equivalent to 252.17Ma ~ 201.3Ma geological period): Clark clam; Late Jurassic-Early Cretaceous (equivalent to 163.5Ma ~ 100.5Ma geological period): wolf fin fish.

The development and future of standard fossils

The standard of standard fossils is relative. Some fossils that were once considered standard were later found to be not so standard. On the contrary, fossils that were originally considered not so standard or not noticed became standard fossils as research deepened, especially in microfossils, such as conodonts, foraminifera, and many species of microalgae fossils have become new standard fossils. Standard fossils will surely play an increasingly important role in future geological work. Friends, let us explore the mysteries of the fossil world together!!!

Note

1. Ma, million years, a time unit commonly used in geology, paleontology and other fields

2. The age values ​​of this era are quoted from the 2016 International Chronostratigraphic Table