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Geologic Time Scale

Anyone who has been to a junior middle school may know that the earth has a history of 4.6 billion years, and many people may know the basic processes and principles of the formation of stratums. In addition, in recent years, people are familiar with the words, such as “Cambrian”, “Jurassic”, “Cretaceous”, and “Quaternary”. However, many people only have a faint glimmer of how do these nouns come about.

We know that we can divide the age of the earth into some units by the age of the stratums, so that we can easily express the evolution of the earth and lives. People used to divide by the situation of the creatures, thus dividing the entire 4.6 billion years into two large units: The era in which the creatures cannot be seen or can hardly be seen is called Cryptozoie eon. The era in which a certain amount of the creatures can be seen is called Phanerozoic eon. The upper limit of Cryptozoie eon is the origin of the earth. However, the lower limit of the era is not a absolutely accurate figure. In general, it can be calculated to 600 million years ago or 570 million years ago. The period from 600 million or 570 million years ago to present is called Phanerozoic eon.

The eon is divided into some eras. According to the common dividing method there are five generations: Archaeozoic era, Proterozoic era, Paleozoic era, Mesozoic era and Cenozoic era. Archaeozoic era generally refers to the period of formation and chemical evolution of the earth, which may be from 4.6 billion years ago to 3.8 million years ago or 3.4 million years ago. The reason why this figure has the deviation of a few hundred millions of years is because the oldest lives or signs of lives that we can master at present still have many uncertain factors. Proterozoic era is immediately after Archaeozoic era. Its lower limit is generally determined before the life explosion in the Precambrian period, which is 570 million to 600 million years ago at present. The two names of Archaeozoic era and Proterozoic era were named by Logan of the United States in 1863. The meanings of the names are the very ancient biosphere and the secondary ancient biosphere. The period from post-Cambrian period to 230 million years ago is Paleozoic era. The name is determined by Sedgwick of the UK. He took the meaning of ancient biosphere in accordance with the idea of Logan. It occurred in 1838. The period from 230 million years ago to 65 million years ago is Mesozoic era. The period from 65 million years ago to present is Cenozoic era. These two eras were named by Phillips of the UK in 1841. The meanings are middle ancient biosphere and the biosphere close to the modern biosphere (See Schedule).The divided units of era are periods. Let’s start with the oldest one. The oldest period is called Sinian period which was named by Grabau of the United States in 1922 in China. He was in the area of Zhejiang Province and Anhui Province and gave the name because the ancient Indians called China the place of sunrise. It is from 1.8 billion or 1.9 billion years ago to 570 million years ago. The lives of this period are mainly bacteria and cyanobacteria. In the later period, eukaryotic algae and invertebrates began to appear.

In 1936, Sedgwick was researching in Welsh to the west of the UK. During the era under the reign of Romans, the Mountain of North Welsh was once known as the Cambrian Mountain so Sedgwick called this period Cambrian period. 33 years later, Lapworth, another British geologist found a stratum in the same region, which is much different from the earlier found Silurian period and Cambrian period. It is between Silurian period and Cambrian period and is apparently a different and representative period. Therefore, he named the period as Ordovician period according to the name of an ancient nation that has lived here. The name of Silurian period came in about 1835, which is earlier than Cambrian period and Ordovician period. Murchison was researching in the west of the UK. The meaning of the name is derived from the name of another ancient Welsh nation. Murchison and Sedgwick named a series of ocean-shaped lithospheres according to the names of the places in 1839 in Devonshire with the Chinese translation of “Mud basin”. The name of carboniferous may firstly in 1822 when Conybeare and Phillips were researching the geology of the UK and found a series of stable lithospheres containing coals. They were formed in a very spectacular coal-forming period. Therefore, it was named after the coals. The name of Permian period was translated by the scientists of China according to the image. It was firstly named as Permian period in 1841 by Murchison according to Permian State (Ufa Plateau of Ural Mountains of Russia) that the area is located in. Later, in Germany, it was found that the stratum of this period has dolomite limestone on the top and red rock stratum at the bottom. This is also the basis that China translated it into “Erdieji”. The above are six periods of Paleozoic era.

There are three periods in Mesozoic era. The first is Triassic period. It was named by Alberti in the southwest of Germany in 1834. There are three series of distinct strata, which is origin of the name. There is the Jura Mountain at the border of Germany and Switzerland. Around 1829, Brongniart was researching there and found there was significant stratum features. Therefore, he study found that there are very obvious stratigraphic characteristics, therefore he named the period after mountains, If Smith of the UK firstly named the period in 1820, the period certainly wouldn’t get the name of “Jurassic” because he was researching the ammonite of this period in the south of the UK. In 1822, two years later, D’Halloy found there were white sediments containing a large amount of calcium on the cliffs on both sides of the English Channel. It was precisely the chalk soil used to make chalks. Thus the period is named as Cretaceous period. What needs to be pointed out is that most of strata of this period in the world are not white, such as the strata in China are mostly red strata of fuchsia color.

Lyell once called Paleozoic Era as the first period, called Mesozoic era as the second age and called Cenozoic era as the third period. In 1829, when researching the geology in certain regions of France, Desnoyers separated the Quaternary period from the Tertiary period according to the Werner’s chronological succession in rocks. In this way, the Cenozoic era is composed by these two periods. The former first period was upgraded into an era of six periods. At the same time, the second period was also upgraded into an era of three periods.

There are also units below the periods, such as “Epoch” which is generally to divide a period into several equal parts. For example, the Cenozoic era is divided into Paleocene epoch, Eocene epoch, Oligocence epoch, Miocene epoch, Pliocene epoch, Pleistocene epoch, Holocene epoch and so on successively.


Ministry of Land and Resources P.R. ChinaDepartment of Land and Resources of Hubei ProvincePeople’s Government of HuanggangHuanggang Municipal Bureau of Land and ResourcesGlobal Geoparks NetworkNational Geopark of China The Geological Museum of ChinaHong Kong UNESCO Global GeoparkShennongjia Global GeoparkTianzhushan Global Geopark




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