Geological Zeitskala (GTS)It is used by geologists, paleontologists and geoscientists. They describe the timing and relationship of the event to the history of the earth. GTS is a chronological dating system that relates the geological state.
Geologists have divided Earth's history into several time intervals. These time intervals do not correspond to the duration of an hour in a day. On the other hand, the duration of the time slots is variable. The reason for this is that geologic time is divided by important events in world history.
For example, the Permian-Triassic boundary is marked by a global extinction event that is wiping out a large percentage of the world's plant and animal species.
Aeons is the longest geologic time span and is hundreds of millions of years old. In the above time period, you can see that the Phanerozoic is the youngest, beginning more than 500 million years ago. The ions are divided into smaller time periods known as ages. In the period above, you can see that the Phanerozoic is divided into three periods: Cenozoic, Mesozoic, and Paleozoic. Very important events in world history are used to determine epochal boundaries.
The eons are divided into smaller time intervals known asseasons. On the time scale above, you can see that the Phanerozoic is divided into three epochs: Cenozoic, Mesozoic, and Paleozoic. Very significant events in Earth's history are used to determine the boundaries of the epochs.
The times are divided intoThe term. The events that delimit the periods are varied, but not as significant as those that delimit the epochs. On the time scale above, you can see that the Paleozoic is divided into the Permian, Pennsylvania, Mississippian, Devonian, Silurian, Ordovician, and Cambrian periods.
More precise time divisions are possible, and Cenozoic periods are often divided intoseasons. The division of periods into epochs can only be done for the most recent part of the geologic time scale. Because the oldest rocks have been deeply buried, severely deformed and highly altered by long-term terrestrial processes. As a result, the history contained in these rocks cannot be interpreted as clearly.
This approach to the exploration of geologic time follows that in "The Grand Canyon", C. Hill, et al., eds., organize the different periods of life from the beginning of the Cambrian. Radiometric dating time data is obtained from this source. Times are in millions of years.
See the Grand Canyon and Grand Staircase sketch for examples covering most of these time periods.
Descriptive information about the various divisions of geologic time is provided below. Lutgens & Tarbuck undertake the task of exploring the history of the earth in one chapter, Chapter 19 of Essentials of Geology. The following brief outline draws on this material and elsewhere to provide a brief overview of Earth's history.
Note that dates in millions of years are representative values. Research publications would provide error bars for such split data; It is not implied here that these limits are known to 3 or 4 significant digits. The division of the geologic column into different periods is largely based on the variety of fossils found, which are considered indicators of a period in Earth's history.
Quaternary [1.8 Ma–0]
On the Lutgens & Tarbuck time scale, the Quaternary is subdivided into the Pleistocene from 1.8 to 0.01 million years ago and the younger Holocene from 0.01 million years ago to the present.
Most of the great movements of the tectonic plates that formed the North American continent took place at the beginning of the Quaternary, and the most important changes in the past were those caused by the action of glaciers and erosion processes. Man arose during this time.
Neogenzeit [23 Ma - 1.8 Ma]
On the Lutgens & Tarbuck time scale, the Neogene Period and the Paleogene Period are combined below and are called the Tertiary Period. Designating this period from around 66 Ma to 1.8 Ma as Tertiary is quite common in the geological literature. It is sometimes referred to as the "age of mammals." Lutgens and Tarbuck further subdivide this Neogene period into the Miocene of 23.8 to 5.3 million years ago and the Pliocene of 5.3 to 1.8 million years ago.
Paleogene Period [66 Ma - 23 Ma]
The Paleogene (or the early part of the Tertiary) represents the period after the great extinction that wiped out the dinosaurs and about half of the world's known species. Lutgens and Tarbuck further subdivide this period into the Paleocene epoch (65-54.8 Ma), the Eocene epoch (54.8-33.7 Ma), and the Oligocene epoch (33.7-23.8 Ma). ).
Cretaceous [145 Ma - 66 Ma]
The Cretaceous is perhaps best known for the great extinction event that marks the Cretaceous-Tertiary boundary. It is commonly known as the K-T extinction, using the first letter of the German spelling of the Cretaceous, and marked the end of the dinosaurs. There is ample evidence linking this extinction to the large impact crater at Chicxulub on Mexico's Yucatan Peninsula.
The Cretaceous, Jurassic, and Triassic periods are collectively known as the "Reptilian Age."
The first flowering plants appeared at the beginning of the Cretaceous period.
Evidence indicates that a vast shallow sea invaded much of western North America and the Atlantic and Gulf coastal regions during the Cretaceous. This created large swamps and led to Cretaceous coal deposits in the western United States and Canada.
Jurassic [201 Ma - 145 Ma]
The distinctive fossil progression characteristic of this period was first found in the Jurassic Mountains of Russia.
Dinosaurs and other reptiles were the dominant species. Birds first appeared in the Jurassic period.
It seems that a shallow sea invaded North America again in the early Jurassic. But near this sea, huge continental sediments were deposited on the Colorado Plateau. These include the Navajo Sandstone, a white quartz sandstone that appears to be blown by the wind and reaches almost 1,000 feet (300 meters) thick.
At the beginning of the Jurassic period, around 200 Ma, Pangea began to break apart and a rift developed between what is now the United States and West Africa, giving rise to the Atlantic Ocean. The westward-moving Atlantic Plate has begun to replace the Pacific Plate. Continued subduction of the Pacific Plate contributed to the western mountains and magmatic activity that resulted in the Rocky Mountains.
Triassic [252 Ma - 201 Ma]
Dinosaurs became the dominant species in the Triassic period.
There is not much marine sedimentary rock from this period in North America. The exposed Triassic strata are composed primarily of red sandstone and shales that lack fossils and suggest a terrestrial environment.
Permian [299 Ma - 252 Ma]
The Permian period takes its name from the Perm region of Russia, where fossil types characteristic of this period were first discovered by geologist Roderick Murchison in 1841. "Amphibians." At the end of the Permian, the once dominant trilobites became extinct along with many other marine animals. Lutgens & Tarbuck refer to this extinction as "The Great Paleozoic Extinction" and comment that it was the largest of at least five great extinctions in the last 600 million years.
Plate tectonics modeling suggests that at the end of the Permian period the continents were all together in the shape of Pangea and that the separations that produced the current alignment of the continents have been occurring ever since. There is much debate about the causes of the then dramatic biological decline. One suggestion is that the fact that there is only one large continent may have made the seasons much more severe than they are today.
Period of Pennsylvania [323 Ma - 299 Ma]
In the Pennsylvania period the first reptiles appeared. During this period, large tropical swamps arose in North America, Europe, and Siberia, which are the source of large coal deposits. Named for the area of silt deposits in Pennsylvania.
Mississippian Period [359 BC - 323 BC]
Amphibians became abundant during this period and towards the end there is evidence of large coal swamps.
Devonzeit [419 Myr – 359 Myr]
The Devonian and Silurian are known as the "Age of Pisces." In the Vomonian period, fish dominated. Primitive sharks evolved. At the end of the Vomián there is evidence of insects with the first insect fossils. From earlier finger-sized coastal plants, land plants evolved and moved away from shorelines. At the end of the Vomián, the fossil evidence points to forests with trees 10 meters high. The Devonian period is named after Devon in the west of England.
In the late Devonian, two groups of bony fishes evolved, the lungfish and lobefinfish, adapted to terrestrial environments, and true air-breathing amphibians. Amphibians continued to diversify with abundant food and minimal competition, becoming more like modern reptiles.
Silurzeite [444 Ma - 419 Ma]
The Silurian period marked the emergence of the first land plants.
Ordovician [485 Ma - 444 Ma]
The Ordovician and Cambrian periods are known as the "Age of Invertebrates", with abundant trilobites. During this time, brachiopods became more common than trilobites, but all but one of their species are now extinct. In the Ordovician, large cephalopods evolved as predators up to 10 meters tall. They are considered the first large organisms. The last part of the Ordovician saw the appearance of the first Pisces.
The data suggests that much of North America was under shallow seas during the Ordovician. There are large accumulations of evaporitic rock salt and gypsum, evidence of shallow seas.
Cambrian [541 Ma - 485 Ma]
The Early Cambrian is the time of the first shell-bearing organisms. Trilobites were dominant in the late Cambrian with over 600 genera of these mud-burrowing scavengers.
The Cambrian marks the time of the appearance of large numbers of multicellular animal fossils, and this proliferation of evidence for complex life is often referred to as the "Cambrian Explosion."
Models of tectonic plate movement point to a very different world in the early Cambrian, with the plate that became North America largely inanimate as a barren plain. Shallow seas rushed in and then receded.
Proterozoikum [2.5 billion – 541 million]
Towards the end of the Precambrian there is fossil evidence of diverse and complex multicellular organisms. Most of the evidence is fossil remains such as footprints and wormholes. It is believed that most Precambrian life forms did not have shells, making it difficult to find fossils. Plant fossils were found a little earlier than animal fossils.
There is no coal, oil, or natural gas in the Precambrian rocks.
Rocks from the Middle Precambrian, 1.2 to 2.5 billion years old, contain most of the iron ore on Earth, mainly ashmatete (Fe2o3). This can be taken as evidence that the oxygen content of the atmosphere was increasing during this period and was abundant enough to react with dissolved iron in lakes and shallow seas. The oxidation process of all this iron may have slowed the buildup of atmospheric oxygen from photosynthetic life. There is an observable end to this iron ore formation, so the rise in atmospheric oxygen should accelerate at that point.
Fossil evidence for life is much less dramatic in the Precambrian period, accounting for about 88% of Earth's history. The most common Precambrian fossils are stromatolites, which have historically been common around 2,000 Ma. Stromatolites are mountains of material deposited by algae. Fossils of bacteria and blue-green algae have been found in the Gunflint Chertrocks in Lake Superior, dating to the 18th century. These are prokaryotic life. Eukaryotic life was found around a billion years ago in Bitter Springs, Australia, in the form of green algae.
Archean Eon [4000 Myr – 2500 Myr]
Evidence of prokaryotic life, such as bacteria and blue-green algae, has been found in southern Africa at 3100 Ma. Iron band formations have been dated to 3.7 billion years ago and since this requires oxygen and that the only source of oxygen molecular at that time was photosynthesis, this justifies life in this period of time. There are also stromatolites dating back to 3500 Myr.
Hadäischer Äon [4500 Myr – 4000 Myr]
The age of the earth is estimated to be around 4.5 billion years based on radiometric dating of the oldest rocks and meteorites. There is evidence of a period of heavy bombardment of the Earth around 4.1 to 3.8 billion years ago, in what is known as the "late heavy bombardment". There is an ongoing debate as to what might have caused this period of intense shock (see wiki). There is no evidence of life in this aeon whose name means "hell".
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