| The poetry of reality|
|We must know. |
We will know.
|A view from the|
shoulders of giants.
The Geologic timeline (also called geologic time scale) is a system of measurement commonly used by earth scientists that relates rock strata to time, providing a rough history of geology and life (through the fossil record) on Earth. The geologic timeline is vast, stretching back to the formation of the Earth approximately 4.5 billion years ago to the present day and into the future until the destruction of the Earth. It is divided into various eons, eras, periods and other denominations to make studying it more practical and distinguish unique periods of time.
- 1 Precambrian
- 2 Paleozoic
- 3 Mesozoic
- 4 Cenozoic
- 5 The Future
- 6 Summary in table form
- 7 See also
- 8 External links
- 9 References
Precambrian (or Pre-Cambrian) is an informal term in geology and paleontology for the time from the formation of the Earth, about 4500 million years ago (mya), to the Cambrian explosion of life that occurred 542 mya, which marked the beginning of the Paleozoic Era and the Cambrian Period. Little is known about the Precambrian, despite the fact that it constitutes the vast majority (about 88%) of our planet's history.
In non-scientific writing, the Precambrian is often imprecisely referred to as a "period" or "era", but "period" and "era" are technical terms of geology, and the Precambrian is itself made up of several periods (such as the Ediacaran) and eras. Precambrian is more accurately described as a supereon, as it consists of several distinct geologic eons: the Hadean, Arcean and Proterozoic.
The Hadean eon saw the formation of the Earth around 4500 mya to around 4000 mya, the formation of the moon and the initial, hostile state of the Earth with heavy volcanism and poison waters when they existed.
Very few traces of this time period remain due to geologic processes, and the few that do are in scattered locations such as Australia and Greenland, and to an extent on the moon as well due to the currently accepted model for its formation in this period.
The Archean is the second eon of the early Earth (4000 mya to 2500 mya), and consisted of higher volcanism and a near-total lack of oxygen in the atmosphere. By the end of the period, the planet would have cooled significantly, allowing more familiar processes to act and for the formation of actual continents and continent bases to begin.
At the beginning there was no functional distinction between the Hadean and the Archean (the division itself is artificial), and at the end it is theorized several continents would have risen and fallen, though less than 10% of Archean rock is known to remain across the planet, in locations spread across the globe.
The most significant part of this time period would be that life began in this era, if not in the previous Eon, though what there was would have been very rudimentary.
The Proterozoic is the final eon of the Precambrian, lasting from 2500mya to 542mya. This eon marks the beginning of life in a way we would understand it (non simple) and the creatures that would ultimately make up the Cambrian explosion would have first evolved in this time period.
Some of the most significant events of this time period would have been the first glacial periods, including a hypothesized time when all except the equator was locked under ice (Snowball Earth hypothesis) and the change of the atmosphere as oxygen rose from almost nothing to the current percentage, as well as triggering a mass extinction of lifeforms to whom oxygen was a poison in the same way carbon dioxide is to modern creatures that breathe oxygen.
The Paleozoic Era is a geological era that started 542 mya and finished 252.2 mya, encompassing the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian geological periods. It is marked in the beginning by the emergence of soft-shelled life, and near the end of the Era, marked by complex plants (the first modern ones), insects, fish, and small reptiles. Sea levels reached ~200m higher than today, due to the warmer climate at the end of the period, which was likely moderate at the start of the era. However due to continental drift it became much warmer in some places and much colder in areas where life was located. This era ended with the greatest known mass extinction in history.
The Cambrian (from Cambria, the classical name for Wales) was a geologic period of time that lasted from 542 to 488 million years ago. It was the first period of the Paleozoic era, and is distinguished from the preceding Precambrian by a spectacular increase in the number of living organisms: specifically, the emergence of multicellular life that possessed hard exoskeletons, and the divergence of many modern phyla like Mollusca, Echinodermata and, notably, Chordata, which of course is the phylum that contains all vertebrate life. The Cambrian Explosion is often misunderstood by creationists; see that article for why. It should also be noted that most of the lifeforms peculiar to the Cambrian looked freaking awesome.[note 1]
The Ordovician (from the Ordovices, a Welsh tribe) is the name given to a geologic period of time following the Cambrian and preceding the Silurian period. It lasted from 488 to 443 million years ago, and was the second period of the Paleozoic era. Some interesting facts include:
- Seas were ~180m higher than present day
- Southern continents were grouped into one named Gondwana
- First land plant spores ~470 million years ago
- Ocean temperatures may have reached 45°C
- An extinction event is thought to have been caused by an ice age, and it started with an extinction event as well.
The Silurian (from the Silures, a Welsh tribe) is a period of geologic time that lasted from approximately 443 to 416 million years ago. It was preceded by the Ordovician period (the boundary between the two is marked by a mass extinction event) and was followed by the Devonian period.
DevonianEnglish county where rocks from this period were first identified) is a period of geologic time that lasted from approximately 416 to 359 million years ago. It was preceded by the Silurian period and followed by the Carboniferous period.
The Devonian period was marked by the formation of large continents, which would later conglomerate into Pangaea. It also witnessed extensive colonisation of the land by plants, and the emergence of the first terrestrial animals (insects and other arthropods). By the end of the period, the first amphibians had appeared in the fossil record. Marine life was dominated by bony fishes, which first appeared in the Silurian period. The end of the Devonian period was marked by a mass extinction event.
The Carboniferous (coal-bearing) is the name given to a geologic period of time that lasted from approximately 359 to 299 million years ago. It was preceded by the Devonian period and followed by the Permian period. Its name is derived from the numerous coal beds that were laid down during this time.
The massive amounts of oxygen in the atmosphere enabled arthropods to grow to enormous sizes (for arthropods—think volleyball size, not monster-movie size).
The Permian (named after the kingdom of Permia, Russia) was the final geological time period of the Paleozoic era, and extended from 290 million years ago to 250 million years ago. It was preceded by the Carboniferous period and succeeded by the Triassic. The start of the Permian was cool and dry; however, by its end the temperature on Earth reached levels higher than at any time since the Cambrian explosion and higher than at any point since. The continents were in one giant landmass called Pangaea.
Young earth creationist claims
Damn-fool Young Earth creationists claim that the split of Pangaea was a result of the flood. Many Young Earth creationists address the high volcanic activity due to the meteorite that is said to have impacted the Earth, and allegedly caused the flood. They state this even though actual scientists claim there was a drought — which, you might recognize, is the opposite of a flood. Indeed, over the course of the Permian, sea levels dropped around 80 meters, creating many basins of salt from evaporated seas.
"The Great Dying"
The Permian Mass Extinction was the worst extinction within the most recent 600 million years of Earth's history. It happened somewhere between 251 and 248 million years ago, marking the transition from the Paleozoic to the Mesozoic Era. This event is estimated to have killed off 90-95% of sea life and about 70% of land organisms. Various hypotheses have been put forth on what caused this event including an asteroid or comet impact, volcanic activity, radiation from a nearby supernova, global warming, or a combination of any or all of the above factors. Many scientists speculate that the formation of Pangaea played a major role in the Permian Mass Extinction, in that all of the continents coming together would have reduced the amount of shoreline and induced desertification of the interior of Pangaea. Furthermore, the amount of land over both the North Pole and South Pole would have caused massive glaciation, and further reduced shallow-water marine habitats by lowering the sea level.
The Triassic is the name given to a geological time period which extended from 251 to 199 million years ago. The Triassic is the start of the Mesozoic Era. It is preceded by the Permian and succeeded by the Jurassic. It followed the largest extinction event known, the P/T, with 95% of species dying. It is the first geological period in which dinosaurs appear. Yay, dinosaurs! Oil, too! Synapsids also survived into and developed in the Triassic; they would later evolve into mammals.
The Jurassic is the geological time period between the Triassic and Cretaceous periods and lasted from 199.6 million years ago to 145.5 million years ago. The Jurassic period is named for the Jura mountains in Europe, where rocks from this era can be found. Dinosaurs were the dominant animal group in this period, and the largest animals to ever walk the Earth emerged during this period, the sauropods—just like in the movie. However, most of the creatures shown in Jurassic Park actually lived during the Cretaceous.
The Cretaceous was a geologic period of time that lasted from approximately 145 to 65 million years ago. It was preceded by the Jurassic period and followed by the Paleogene period, the latter boundary also forming the demarcation between the Mesozoic and Cenozoic eras. It was the last period of the "Age of Reptiles": dinosaurs, pterosaurs and marine reptiles were the dominant global megafauna.
The end of the Cretaceous period was marked by a mass extinction event known as the K-Pg (Cretaceous-Paleogene; the "K" is from the German Kreide for chalk) Extinction. It was formerly known as Cretaceous–Tertiary (K–T) boundary. The boundary consists of a thin deposition layer with abundant iridium. Iridium is scarce in the Earth's crust but is abundant in asteroids and other space rocks. The layer has been conclusively shown to have been caused by an impact by an asteroid or possibly a comet) named Chicxulub that struck off of what is now the Yucatán Peninsula of Mexico at 66 mya. The asteroid was clearly a devastating extinction level event, as evidenced by the fossil record below and above the K-Pg boundary. There is still some scientific debate about whether the massive Deccan volcanic eruptions (in what is now India), which lasted from about 66.25-65.5 mya, had a contributory effect to the extinctions. The extinction event killed off all large animals, including all dinosaurs other than birds. In addition, many marine reptiles, several mollusc groups, and other organisms went extinct. This is the most famous and widely known mass extinction (due to the mass appeal of dinosaurs), though it isn't the largest or most recent. The largest event is considered to be the Permian–Triassic extinction event, and the most recent is occurring now, the Holocene extinction event.
The Cenozoic Era is a geologic period that includes the last 65 million years. It begins with the mass extinction of non-avian dinosaurs 65 million years ago. The Cenozoic Era is divided into Paleogene and Neogene periods, which are further broken up into nine epochs. Given the relatively recent time frame, the Cenozoic period is the best understood of all geological time periods including everything from weather features, temperature, geological changes, changes in life forms including detailed evolutions, and extinctions.
The Paleogene was a geologic period that lasted from approximately 65 to 23 million years ago. It was also the first period of the Cenozoic era. It was preceded by the Cretaceous period and followed by the Neogene period. (Formerly the Paleogene and Neogene were lumped together as the Tertiary period.) The Paleogene period is itself divided into three epochs: the Paleocene, Eocene and Oligocene.
The Paleogene period began with the K-T extinction, an event that removed most of the then-dominant dinosaurs from the ecosystem, along with many other groups, and allowed mammals and the one surviving group of dinosaurs, birds, to proliferate.
The Neogene was a geologic period that lasted from approximately 23 to 2.6 million years ago. Alternatively, it has been argued that the current Quaternary period should be included within the Neogene period. It followed the Paleogene period, and was the second period of the Cenozoic era.
It is subdivided into two epochs: the Miocene (23 to 5.3 million years ago) and the Pliocene (5.3 to 2.6 million years ago).
During the Neogene period, the continents roughly assumed their present positions and the world's flora and fauna evolved into forms of which the majority would be comparable with modern species. The genus Homo, which would eventually give rise to humans (us!), also appeared at the end of the Neogene.
The Quaternary is the current geologic time period, which began approximately 2.6 million years ago. It is divided into two epochs: the older Pleistocene (2.6 million to 11,700 years ago) and the current Holocene (11,700 years ago to the present). Its status, however, is disputed, as some geologists claim that it should be included within the preceding Neogene period.
The name Quaternary itself derives from the obsolete Primitive (or Primary), Secondary and Tertiary periods which were classified by the Italian geologist, Giovanni Arduino, in 1760. The Primitive referred to crystalline basement rocks, Secondary to consolidated sedimentary rocks, and Tertiary to alluvial rocks that were thought to have been deposited by the Global Flood but now corresponds to the period of time covered by the Paleogene and Neogene periods.
Whether it remains a separate period or not, the Quaternary is of particular importance to humanity as this is the time when Homo sapiens evolved. The period has also been marked by frequent glacial periods, of which more are forecast to come (unless global warming changes the plan and ends the ongoing ice age).
Assuming that the processes of the past continue to operate as they have and something else doesn't drastically change the current geologic motions, the Pacific Ocean will be subducted under the Eurasian and North American Plates as the Atlantic Ocean expands, pushing the two continents together into a new super-continent, nicknamed "Amasia" (not to be confused with the Amero) by some, potentially centered around the North Pole.
Beyond that we have only wild speculation as to what will happen, as Amasia is predicted to form around a hundred million years in the future and from there it's anybody's guess. However Geologic time will continue until the world itself ceases to exist, even if only as a dead husk orbiting a long dead star.
Summary in table form
Quaternary (1.8 ma to today)
|Holocene (11,000 years to today)|
|Pleistocene (1.8 mya to 11,000 yrs)||Homo erectus and Homo sapiens appear|
|Tertiary (65 to 1.8 mya)||Pliocene (5 to 1.8 mya)||Ape-like ancestors of modern humans (Hominids), the Australopithecines|
|Miocene (23 to 5 mya)||Grazing horses, antelopes appear|
|Oligocene (38 to 23 mya)||
Radiation of more modern animals: most modern bird forms have appeared; most modern mammals have appeared.
|Eocene (54 to 37 mya)||Some modern mammals appear: advanced primates; camels, cats, dogs, horses & rodents|
|Paleocene (65 to 54 mya)||Small mammals radiate|
(245 to 65 mya)
Cretaceous (146 to 65 mya)
Major extinction includes non-avian dinosaurs and ammonites (K-T)
|Jurassic (208 to 146 mya)||Appearances include: birds; crabs; frogs and salamanders|
Dinosaurs radiate to dominate the land
|Triassic (245 to 208 mya)||Major extinction event: tabulate corals and conodonts disappear — ammonoids, reptiles and amphibians decimated|
Appearances include: dinosaurs; crocodiles; marine reptiles; turtles and mammals
Major groups of seed plants appear
Permian (286 to 245 mya)
(360 to 286 mya)
|Pennsylvanian (325 to 286 mya)||Conifers and many winged insects appear|
|Mississippian (360 to 325 mya)||Reptiles appear
Trilobites become scarce
|Devonian (410 to 360 mya)||Mass extinction (F-F)
Appearances include: insects; sharks; amphibians (tetrapods); lung fishes and earliest seed plants
|Silurian (440 to 410 mya)||Jawed fish and vascular plants appear|
|Ordovician (500 to 440 mya)||Mass extinction
First land plants; bryozoans appear. Trilobites begin to specialize.
|Cambrian (544 to 500 mya)||Tommotian (530 to 527 mya)||Appearance of hard parts - fossils become common. Appearances include: vertebrates; jawless fish; small shelly animals; conodonts; trilobites radiate repeatedly and reach their peak diversity.||First major radiation of animals|
(2500 to 544 mya)
|Extinction at end of Vendian
Macroscopic fossils of soft-bodied organisms.
|Neoproterozoic (900 to 544 mya) - Late||
Macroscopic fossils of soft-bodied organisms.
|Mesoproterozoic (1600 to 900 mya) - Middle||Eukaryotic organisms proliferate
|Paleoproterozoic (2500 to 1600 mya) - Early||Eukaryotic organisms appear (acritarchs?)
Oxygen-releasing photosynthesizers appear, changing the atmosphere
Three domains' ancestors diverge
First life appears
(4500 to 3800 mya)
|Earth possibly sterilized by heavy bombardment|
- A creationist explanation of the mass extinction event
- Scientists' view of the Permian
- Palaeos.com on the Devonian
- The Permian
- How they reconcile accepting the existence of Pangaea and its sundering into today's continents with Young Earth Creationism is a possibly interesting question.
- Haq, B. U.; Schutter, SR (2008). "A Chronology of Paleozoic Sea-Level Changes". Science 322 (5898): 64–68. See here
- The Permo-Triassic extinction
- Devastation detectives try to solve dinosaur disappearance: Retracing the terrifying, mysterious final days of the dinosaurs by Thomas Sumner (2:30pm, January 25, 2017) Science News.
- Some lucky birds escaped dino doomsday: Feathers, wishbones and more were a dino thing before they were a bird thing by Susan Milius (2:30pm, January 25, 2017) Science News.
- Unless of course you believe non-avian dinosaurs still exist, or that they were killed in a flood just 6000 years ago. If either or both of those are your take, well, we can't really help you
- Geologic time scale
- National Geographic: Quaternary Period
- Geologic time scale
- The super continent Amasia around the north pole
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