Geologic timeline - RationalWiki Geologic timeline v - t - e 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. Contents [ edit ] Precambrian 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.

The Precambrian saw the origin of life , the evolution of photosynthesis , the transformation of Earth's atmosphere into its modern form, and the creation of iron ore. 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. [ edit ] Hadean 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.

[ edit ] Archean 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 continent and continent bases to begin. At the beginning there was no functional distinction between the Hadean and the Arcean (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, if not in the previous Eon, began in this era, though what there was would have been very simple. [ edit ] Proterozoic 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. [ edit ] Paleozoic 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 (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 come places and much colder in areas where life was located. This era ended with the greatest known mass extinction in history . [ edit ] Cambrian 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 Pre-Cambrian period 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.

[ edit ] Ordovician 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 is thought to have been caused by an ice age , and it started with an extinction event as well. [ edit ] Silurian Yay, fish! 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. The Silurian period saw the first appearance of coral reefs and jawed fish in the fossil record, in addition to widespread terrestrial plant life.

[ edit ] Devonian The quarry in Devon whose rocks gave the period its name. The Devonian (from Devon, the English 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. [ edit ] Carboniferous 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 supercontinent Pangaea formed during the Carboniferous period. Animal colonisation of the land increased, with the diversification of arthropods and amphibians . It was during the Carboniferous that most of today's so-called " fossil fuel " deposits were laid down. It is often divided into the Mississippian and Pennsylvanian time periods. The massive amounts of oxygen in the atmosphere enabled arthropods to grow to enormous sizes (for arthropods—think volleyball size, not monster-movie size). [ edit ] Permian The P-T boundry 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. [1] 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 .

[ edit ] Young earth creationist claims Young Earth creationists claim that the split of Pangaea was a result of the flood [2] . 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 true scientists claim there was a drought - which is the opposite of a flood. Indeed, over the course of the Permian sea levels dropped around 80 meters, [3] creating many basins of salt from evaporated seas. [ edit ] "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. [4] 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, as well as induces 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. [ edit ] Triassic 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 . [ edit ] Jurassic DInosaurs! 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. [ edit ] 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. [ edit ] K-T Extinction The end of the Cretaceous period was marked by a mass extinction event known as the K-T (Cretaceous-Tertiary [5] ) Extinction, now also known as the K-Pg Extinction using the more modern timescale.

It is believed to be caused by a combination of a meteorite impact and volcanic activity, and resulted in the extinction of nearly all of the hitherto dominant dinosaurs ( birds survived), in addition to the pterosaurs, many marine reptiles, several mollusc groups, and other organisms. 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 may well be occurring now. [ edit ] Cenozoic The Cenozoic Era is a geologic period that includes the last 65 million years. It begins with the mass extinction of non-avian dinosaurs [6] 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.

[ edit ] Paleogene 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. [ edit ] Neogene 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). [7] 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. [ edit ] Quaternary The Quaternary is the current geologic time period, which began approximately 2.6 million years ago. [8] 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). [9] 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). [ edit ] The Future 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. [10] 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. [ edit ] Summary in table form Silurian Silurian Period The Silurian was the third division of the Paleozoic era of the geologic time scale spanning from approximately 395 and 440 million years ago, preceded by the Ordovician and followed by the Devonian. Roderick Impey Murchison, a Scotsman, who eventually became the director of the Geological Survey of Great Britain, was responsible for naming the period. The term Silurian comes from Silures, the name of a celtic tribe of people that lived along the border of England and Wales before the time of the Romans. In the early 1800s, British geologists recognized rocks in this area that contained a distinctive assemblage of fossils, different from the fossils in both underlying strata of the Ordovician and overlying strata of the Devonian. Silurian fossils, identical to those in Britain, were subsequently discovered in many other regions of the world, including the Great Lakes region of North America.

Its stratigraphy is subdivided into four epochs: the Llandovery, the Wenlock, the Ludlow, and the Pridoli. Each epoch is distinguished from the others by the appearance of new species of graptolites. The Llandovery (428-440 million years ago) preserves its fossils in shale, sandstone, and gray mudstone sediment. Its beginning is marked by the appearance of the graptolites Parakidograptus acuminatus and Akidograptus ascensus. The Llandoverian epoch is subdivided into the Rhuddanian, Aeronian, and Telychian stages. The start of the Wenlockian epoch (428 - 421 million years ago) is marked by the appearance of Cyrtograptus centrifugus. The fossils are found in siltstone and mudstone under limestone. Missing from the fossil record of the Wenlock was the conodont Pterospathodus amorphognathoides, present in earlier strata. This is an epoch with excellent preservations of brachiopod, coral, trilobite, clam, bryozoan, and crinoid fossils.

The Wenlock is subdivided into the Sheinwoodian and Homerian stages. The Ludlow (421 - 414 million years ago) consists of siltstone and limestone strata, marked by the appearance of Neodiversograptus nilssoni. An abundance of shelly animal fossils is visable. The Gorstian and Ludfordian stages make up the Ludlow epoch. The Pridolian, the final epoch of the Silurian, is recognized by platy limestone strata rich in cephalopods and bivalves. It is marked by the appearance of the index fossil Monograptus parultimus, and also by two new species of chitinozoans, Urnochitina urna,and Fungochitina kosovensis, which appear at the base or just above the base of the Pridoli. The Beginning and the End The Silurian world was vastly different in many ways than the world of today. The shapes and distribution of the continents were drastically different from present day, and shallow seas covered much of the continental areas. For example, the equator passed through North America, and a nearly continuous inland sea stretched between New York and Nevada.

The Silurian is bracketed in time by two major mountain-building episodes: the Taconian orogeny of the preceding Ordovician period, and the Acadian orogeny of the following Devonian. Convergence of tectonic plates, which had begun during the Ordovician, crumpled the sedimentary rocks that had been accumulating in the Caledonian geosyncline of northwestern Europe. Ordovician-Silurian extinction, about 439 million years ago, was a direct result of a drop in global temperature causing glaciers to form and sea levels to drastically plunge. The maximum global fall in sea level was as much as 170 meters resulting in the drainage of immense areas of former marine habitat. The consequential extinction was roughly 25 percent of marine families and 60 percent of marine genera. Among the hundred families which disappeared, the most concerned groups were Bryozoa, Brachiopods, solitary Corals, Trilobites, Graptolites, Echinoidea and Crinoids. Resumption of environmental conditions favorable to faunal recovery from the late Ordovician extinctions was the most significant geologic event of the Silurian Period.

Basal Silurian strata reveals a rapid rise in the level of the sea, which reflooded vast continental platforms. The end of the Silurian saw the forming of massive mountain ranges along the edges of the two continental margins, and in England a move to deposition of sediments derived from the new mountains - the Devonian system.

Climate/Ecological communities The Changing Earth During the Silurian and Important Implications for the Environment and Life within It Silurian underwent a stabilization of the earth's general climate, drawing the previous pattern of erratic climatic fluctuations to a close Changes resulted in the melting of large glacial formations that contributed to a significant rise in the levels of major seas Earth entered a warming greenhouse phase, with regions of 65� or more from the equator were covered with glacial ice Greenland and parts of North America were about 15� from the equator (sedimentary rocks found in these areas provide clear-cut evidence of deposition in a tropical environment) Within 40� of the equator, coral reefs grew in warm marine waters Hot, arid lands were present, and evaporate minerals-such as salt and gypsum-precipitated from former inland waters Warm shallow seas covered much of the equatorial landmasses Note: In contrast to the Late Ordovician event, these fluctuations did not strongly affect the shelly bottom-dwelling invertebrates on continental platforms. Tropical reefs were common, formed by tabulate and rugose corals, stromatoporoid organisms, bryozoa, and calcareous algae.

Reefs of all Silurian ages are known, but their development probably reached a climax during Wenlock time. Several thousand have been recognized from outcrop and subsurface evidence across a tract of 800,000 square km surrounding the Great Lakes region of North America. Trilobites, cephalopods, gastropods, echinoderms, and graptolites were common and diverse. Continental Drift During the Silurian , the Earth witnessed many changes in the way in which landmasses were distributed around the globe. Although there were no major volcanic events, a thawing of glaciers and rise in sea levels produced varying periods of continent coverage and exposure. The variation of ocean levels occurred alongside the process of continental fragmentation and grouping that occurred from the Cambrian to the present.

The Silurian World Vast north polar ocean and the south polar supercontinent known as Gondwana along with a ring of approximately six continents A large portion of the Rodinian landmass was fragmented, and those fragments drifted toward the equatorial region Fragments eventually assembled the super-continents of Laurussia and Laurasia due to a series of plate collisions Modern Philippine islands were most likely inside the Arctic Circle, while Australia and Scandinavia resided in the tropics South America and Africa were comparatively over the South Pole The period is marked by major orogenic events in eastern North America and in northwestern Europe forming mountain chains there. This was known as the Caledonian Orogeny. Large igneous rock formations of the Middle Silurian arose, such as those in Central Europe, as well as light sedimentation throughout the Baltic region. Baltica and the attached microcontinent Avalonia begin colliding with North America. In the North Atlantic area the Silurian marked the closure of the great 'Iapetus' Ocean that separated North America from Northern Europe.

At that time, even though the boundary of the Eastern edge of North America was more or less in the same position as today, Newfoundland and a portion of Eastmost America was on the South of the ocean together with England and Ireland. Northern Ireland and Scotland were on the Northern flank. Adaptive radiations The Silurian is a time when many biologically significant events occurred. In the oceans, there was a widespread radiation of crinoids, a continued proliferation and expansion of the brachiopods, and the oldest known fossils of coral reefs. The Silurian was also a remarkable time in the evolution of fishes. Not only does this time period mark the wide and rapid spread of jawless fish, but also the highly significant appearances of both the first known freshwater fish as well as the appearance of jawed fish. Other marine fossils commonly found throughout the Silurian record include trilobites, graptolites, conodonts, corals, stromatoporoids, and mollusks. The first good evidence of life on land is also present, including relatives of spiders and centipedes, and also the earliest fossils of vascular plants.

While it is possible that plants and animals first moved onto the land in the Ordovician, fossils of terrestrial life from that period are fragmentary and difficult to interpret. Silurian strata have provided likely ascomycete fossils, as well as remains of the first arachnids and centipedes. Several small extinction and radiation events in the evolution of nektonic and pelagic organisms appear to be linked to Silurian fluctuations in sea level. Five graptolite radiations are recorded in the Silurian System. The Wenlock radiation, for example, involves distinct new genera such as Cyrtograptus and as many as 20 new species. Among conodonts, a significant radiation is indicated by species within the Pterospathodus amorphognathoides biozone, which straddles the Llandovery�Wenlock boundary. Extinction of key species followed by the origination of several new species during the Wenlock epoch was one of the most drastic changes in the Silurian conodont succession.

Fish of the Freshwater and Marine Environments The jawless Ostracoderms were bony skinned and heavily armored Acanthodians, the first jawed fishes, radiated during this time. Jaws probably evolved from gill supports, and they developed paired fins as well as scales and plates. The bony fish, Actinopterygii or ray-finned fish, were the largest group of fish. These evolved during the very end of the Silurian, about 408 million years ago. There group currently dominates the seas.

Land Colonization and Adaptive Radiation of Vascular Plants Occurred during most of the Silurian Period, although activity clearly was restricted to coastal lowlands Believed to have radiated from algae, species belonging to the genus Cooksonia named after Isabel Cookson an intensive collector of plant fossils were among the first and most successful vascular land plants Fossils found in Ireland indicate these plants were small (~ 6 cm) with smooth, branched stems bearing spore sacs at their tips Problems on Land Respiration and ways to extract gases from the air Reproduction on dry land Danger from the outer universe, aka,ultraviolet rays Adaptive Solutions Algae in water helped their brothers by producing ozone during photosynthes protecting land creatures from harmful UV rays Terrestrial plants developed a waxy outer coating to prevent water loss, stomata, reproductive structures that could function on land, and complex water circulation system with horizontal stalks Photosynthesis took place entirely within the leafless stems Phloem and xylem (aka.

vascular tissue) allowed plants to increase their habitat range from damp moist environments to drier environments Spores had very tough walls which were excellent protection against dessication and an excellent fossilizing very agent Three otherimportant lineages of seedless plants: club mosses (Lycophyta), the horsetails (Sphenophyta), and the ferns (Pterophyta) With the introduction of these plants onto land, the terrestrial world began to alter. Plants help to break down rocks and contribute their own decaying remains to create rich, productive soils not available before this time. Plants also changed the pattern of erosion by binding soil with their roots and retaining runoff water. Enigmatic plants: Still a Mystery At the time of the first Cooksonias a completely different group of plants has evolved, which tried to colonize the land. Three most commonly discussed: Nematothallus, Parka and Pachytheca. "Evolutionary experiment to colonize the land" These plants have lost the increasing competition with the successful higher plants. Research for the real nature and the ecology of these plants is still in full progress. Extinctions There were two mid Silurian graptolite extinctions and subsequent diversifications.

This is believed to be due to slow recovery of grapolites after the Ordivician mass extinction. Fossil resources Famous Silurian fossil sites include the Brownsport Group in Tennessee and Brandon Bridge, Wisconsin. Silurian creatures adopted as state fossils include New York's water scorpion Eurypterus remipes and Wisconsin's trilobite Calymene celebra. Silurian features of the United States include the following: The Appalachians the fleshy appendage that tethers a shell to the seafloor Silurian Period- unit of geologic time that began approximately 438 million years ago and ended 408 million years ago. The Silurian Period is the 3rd period of the Paleozoic Era and can be determined by its characteristic fossil contents. Invertebrates and fishes were common during the Silruian. Land Plants began to appear near the end of this period. The Silurian Period contains three epochs: The Upper Silurian, Middle Silurian, and Lower Silurian. Literature Bassett, M. G. and J. D. Lawson, eds. Autecology of Silurian Organisms. The Palaeontological Association; London.

1984. Chaloner, W. G and J. D. Lawson, eds. Evolution and Environment in the Late Silurian and Early Devonian. The Royal Society; London. 1985. Dawson, J. W. Fossil Plants of the Devonian and Upper Silurian. Dawson Bros.; London. 1871. Jeppsson, Lennart. Aspects of Late Silurian conodants. University of Lund; Sweden. 1974 Johnson, J. Harlan et. al. Studies of Silurian (Gotlandian) Algae Vol. 54, Num. 1. Colorado School of Mines; Colorado. 1959. Paleozoic Era - Cosmeo Paleozoic Era Grades: K-12 Overall Rating: Major division of geological time, preceded by the PRECAMBRIAN ERA, and followed by the MESOZOIC ERA, (qq.v.), and including the CAMBRIAN PERIOD,, ORDOVICIAN PERIOD,, SILURIAN PERIOD,, DEVONIAN PERIOD,, CARBONIFEROUS PERIOD,, and PERMIAN PERIOD, periods (qq.v.).

The Paleozoic began about 570 million years ago and ended about 225 million years ago. The evolution of life, from primitive, multicellular, free-floating forms in the sea to advanced groups on land, can be traced by fossil remains in rock strata of the Paleozoic era. See EVOLUTION,; GEOLOGY. For further information on this topic, see the Bibliography, sections 417. Geology, 420. Earth, 436. Paleontology. Save to My Favorites SAVING My Favorites is a perfect place to organize materials for a school report. To access this feature, sign up for a FREE 30 day trial now! geological time periods geological time periods The time periods are very important to a palaeontologist. The table below is a very simple Geological Time Line. Click on the time period you wish to invisigate. Tertiary Period This Era started 65 million years ago and finished 2 million years ago. This Era is split into 5 parts.This was the Era of mammals. Life in the Tertiary Era On land, the age of the mammals was beginning. Rodents evolved, as well as gliding mammals and the early primates.

Sharks and fish took over from marine reptiles. Towards the middle of this Era, the ancestors of elephants, horses, cattle, pigs, rhinos and deer appeared. Other mammals such as whales and sea cows took to the water. Other groups of animals were also evolving, including ants and bees, starlings and penguins, moles, camels, cats, dogs and bears. Towards the end of this period , grazing hoofed animals spread and diversified. The ancestors of humans appeared in Africa. Plant life in the Tertiary Era In the early parts of this era, flowering plants continued to spread and diversify. Towards the end of this era the climate cooled, grasslands took over from the forest Cretaceous Period Started 144 million years ago and lasted to 65 million years ago. This was the period of the explosion of flowers. The explosion of flowers Up until the beginning of the Cretaceous Period, the distribution of spores and pollen was a risky business. In the Cretaceous Period new and more effective ways of spreading pollen developed. Flowering plants were now evolving with a partnership with the insects. Life in the Cretaceous Period Giant turtles and marine reptiles dominated the oceans. On land snakes evolved.

There were new kind of dinosaurs. Insects such as moths and butterflies, got there food from the new flowers. At the end of the period, there was a mass extinction which saw ammonites, ichthyosaurs, and many other marine groups to disappear and the dinosaurs became extinct. Plant life in the Cretaceous Period The following plants appeared and evolved relationships with insects for pollination. The flowers spread rapidly over the land. Jurassic Period The Jurassic period started 213 million years ago and lasted until 240 million years ago. This was the first period to have birds. Life in the Jurassic Period Turtles and crocodiles increased in numbers and variety. New species of plesiosaur and ichthyosaur arose. On land insects were thriving including ancestors of modern ants, bees, earwigs, flies and wasps. The first bird appeared. Dinosaurs ruled the land. Plant Life in the Jurassic Period Plants spread across the land as the climate became wetter. The of the modern cypresses, pines and redwoods appeared in the forests. Triassic Period This period started 248 million years ago and finished 213 million years. This period was the beginning of the Mesozoic era.

Life in the Triassic Period Dinosaurs and other reptiles became the dominate land animals. Frogs appeared and later the first tortoises, turtles and crocodiles. The first mammals appeared. Plant Life in the Triassic Period The cone-bearing plants diversified forming forests of cycads, monkey-puzzle trees, ginkgoes and conifers. Permian Period This period started 286 million years ago and went to 248 million years ago. This period was the period which reptiles took over. Life in the Permian Period Ammonities were still very abundant. Modern corals began to take over the early reefs. In the early part of this period amphibians dominated fresh water. Aquatic reptiles evolved. Towards the end of this period over 50% of the animal families disappeared, including many amphibians, ammonities and trilobites. Reptiles took over from amphibians on land. Plant Life in the Permian Period Conifers appeared and spread inland and up mountains. The southern land mass was dominated by forests of large seeding ferns. Carboniferous Period This period went from 360 million years ago to 286 million years ago.

During this period insects were everyware and the decaying trees during this time produced the coal known today Life in the Carboniferous Period Ammonites and Brachiopods became more abundant. The age of amphibians appeared. Insects including grasshoppers, cockroaches, silverfish, termites, beatles and giant dragonflies also evolved. In the late part of this period the first reptiles appeared. Plant Life in the Carboniferous Period Dence forests of giant clubmosses, horsetails, tree ferns and sead plants up to 45m tall. The undecomposed remains of these forests develop into coal. Devonian Period The Devonian period started at about 410 million years ago and ended about 375 million years ago. This period was the age of the fish. Life in the Devonian Period During this period there was a rapid evolution of fish, including sharks and rays, lobe finned fish and ray finned fish. Ammonities increased in population. Giant squid up to two meters long hunted the seas. Many arthropods including spiders and wingless insects invaded the land.

Plant Life in the Devonian Period Plants spread from the margins of the water to cover large areas of land in dense forest. Some trees developing up to 38m high. Silurianan/ordovician Periods These time periods from 500 million years ago to 435 million years ago. In these periods powerful predators and reefs began to be built. Life in the Ordovician and Siluran Periods In these periods there was a great increase in filter feading animals. These included sea mats, sea lilies, brachiopods, molluscs and graptolites which all met their peak in the Ordovician period. Durying the Siluran period rugose corals were very active reef builders. This was the age of the great preditors including sea scorpions, and the first jawed fish. Brachiopods and trilobites thrived. Plant life in the Ordovician and Siluran Periods The first true plants first apeared in the late Ordovician period. In the Siluran period plant life surounded the margins around the water. Cambrian Period The Cambrian period began about 570 million years ago.

It lasted for about 70 million years. The period began with an astonishing explosion of evolution, during which most of the major groups of animals we know today made their first appearances on Earth. The Cambrian Explosion The Cambrian explosion is one of the biggest mysteries in the history of life. It took 2.5 billion years for simple cells to become more complex cells. It took another 700 million years for multicellular creatures to appear. Then, in just 100 million years, came a tremendous variety of multicellular animals. For over 500 million years not a single new basic body plan was evolved. The Cambrian period sea level rose and fell making some populations extinct. As the Cambrian period went on, animals evolved new and more specialized ways of feeding thus creating a greater variety of animals. Life in the Cambrian Period In the huge burst of evolution creatures including microscopic organisms, sponges, starfish, sea urchins, sea lilies and velvet worms all evolved in this period. The first shelled animals also appeared; trilobites and brachiopods who then dominated the seas. Later in the period molluscs and primitive fish evolved.

Trilobites were a major step in the evolution because they had the first eyes. Plant Life in the Cambrian Period In the Cambrian seas the only plant life was primitive algae and seaweeds. Precambrian Era The Precambrian Period starts with the birth of Earth to the appearance of many-celled animals, about 570 million years ago. Methane and other gases were the only gases in the Earth primitive atmosphere. These gases dissolved into the masses of water which covered the Earth, forming a complex chemical "soup". Lighting discharges on this soup acted in a way that caused the chemicals to react, forming more complex chemicals very similar to the ones in living cells. After a few million years these chemicals developod the ability to reproduce. In the soup there was also fat globules. If the soup was stirredviolently by the wind, the complex chemicals may have become trapped within the fat globules. In time these structures evolved into lining cells surrounded by fatty membranes. Life in the Precrambrian seas Some of the first life in the sea was stromatolites, which appear to be made up of lots of rings of limestone, with orgaic layers in between.

Later life in these sea saw a range of soft body creatures, including jellyfish, worms and leaf like sea pens. The only evidice left from that period where trace fossils left by the animal. Ordovician period facts, information, pictures | Encyclopedia.com articles about Ordovician period COPYRIGHT 2002 The Gale Group Inc. Ordovician The Ordovician period (500 to 440 million years ago) comes after the Cambrian in the early Paleozoic era. The period is named for a Celtic tribe named the Ordovices who once lived in the area of Wales (in Britain ) where the rocks were first studied. Ordovician limestones are over 6.4 kilometers (4 miles) thick in places and are found on all continents except Antarctica . The uniformity and thickness of the bed indicates a long period of warm and stable climate that allows them to develop. In fact, the Ordovician period was as remarkable for the diversity of its species as the Cambrian period was for the appearance of most major phyla . A burst of evolutionary creativity in shape, size, and function tripled the number of marine species that appeared.

Specialization became the dominant theme of life, with new forms filling every possible niche . The appearance of highly efficient predators such as the nautiloids and the lobster-size sea scorpions forced the marine community to evolve protective strategies or disappear. Various species responded by developing larger size, thicker shells, or more elaborate defenses. A proliferation in the shapes of the shells of bivalve mollusks allowed them to burrow deeply into sand or mud. Other mollusks learned to swim freely by rapidly clapping their valves together. And still others developed intricate teeth-and-socket arrangements that allowed them to close so tightly that they were almost impossible to open. Exploring the oceans of the Ordovician world would have been quite similar to exploring the oceans of today. Sea urchins, starfish, and sea lilies lived in profusion among the rocks. The first great coral reefs appeared and gave shelter to crustaceans of all kinds. Sea mats, sea snails, and sea cucumbers abounded in the tide pools. A huge diversity of bivalve mollusks made their slow way across the muddy ocean floor, leaving their tracks and burrows in the fossil record . Era The Columbia Encyclopedia, 6th ed.

Copyright The Columbia University Press Ordovician period (ôrdəvĬsh´ən) [from the Ordovices, ancient tribe of N Wales], second period of the Paleozoic era of geologic time (see Geologic Timescale , table) from 505 to 438 million years ago. It was similar to the preceding Cambrian period , with shallow seas spread for most of the time over the British Isles, Scandinavia, the Baltic region, the Mediterranean region, a large part of Siberia, and much of North America. The Ordovician rocks are chiefly sedimentary. Because of the restricted area and low elevation of the solid land, which set limits to erosion, marine sediments that make up a large part of the Ordovician system consist chiefly of limestone; shale and sandstone are less conspicuous. The Ordovician of North America can best be studied in New York state. In the Early, or Lower, Ordovician epoch, also called the Canadian epoch, the waters spread over the Appalachian area and deposited the Beekmantown limestone, then withdrew generally, to return and deposit the Chazy limestone of the lower Middle Ordovician, also known as the Champlainian epoch.

In the interval between Beekmantown time and Chazy time, large areas, chiefly outside New York, were apparently covered with wind-blown sand which became the St. Peter sandstone. In the Middle Ordovician the sea spread over North America to a greater extent than in any other period and laid down the Trenton limestone, which in its eastern section is overlaid or intercalated with the Utica mud shale. In the east, increased erosion of the land subsequently led to the deposition of other shales, which became more and more sandy toward the end of the period. The close of the Ordovician was marked by more general earth disturbances than the close of the Cambrian. The Taconian disturbance created a chain of fold mountains extending from Newfoundland to New Jersey and was accompanied by volcanic activity. The later start of the Acadian-Caledonian uplift may have also been the start of the proto-Atlantic Ocean. Among the economic resources of the Ordovician strata are oil, natural gas, the lead and zinc of Wisconsin, Iowa, and Illinois, the "Portland cement rock" of Pennsylvania and New Jersey, Vermont marble, and the calcium phosphate of the Tennessee limestone. The Ordovician seas were rich in animal life.

The most characteristic invertebrates were minute graptolites, other numerous forms being brachiopods, bryozoans, and trilobites. Some cystoids and crinoids appeared; there were a few corals and many cephalopods. Especially noteworthy was the appearance of a few primitive, fishlike vertebrates (jawless fishes) and tiny land plants resembling liverworts . Cite this article COPYRIGHT 2003 The Gale Group, Inc. Ordovician Period In geologic time , the Ordovician Period, the second period of the Paleozoic Era , covers the time roughly 505 million years ago (mya) until 438 mya. The name Ordovician derives from that of the Ordovices, an ancient British tribe. The Ordovician Period spans three epochs. The Lower Ordovician Epoch is the most ancient, followed in sequence by the Middle Ordovician Epoch, and the Upper Ordovician Epoch.

The Ordovician Period is divided chronologically (from the most ancient to the most recent) into the Tremadocian, Arenigian, Llanvirnian, Llandeilian, Caradocian and Ashgillian stages. Much of the continental crust that exists now had already been formed by the time of the Ordovician Period and the forces driving plate tectonics actively shaped the fusing continental landmasses. Near the margins of the continental landmasses, extensive orogeny (mountain building) allowed the development of mountain chains . The fossil record provides evidence to support the demarcation of the preceding Cambrian Period from the Ordovician Period. Drastic changes of sea levels resulted in massive extinctions among marine organisms. In accord with a mass extinction, many fossils dated to the Cambrian Period are not found in Ordovician Period formations. The fossil record establishes that vertebrates existed during the Ordovician Period. As with the Cambrian Period, the Ordovician Period ended with a mass extinction of nearly a third of all species. This mass extinction, approximately 438 mya, marked the end of the Ordovician Period and the start of the Silurian Period .

Although there is no evidence of an occurrence equivalent to the K-T event , it is possible that an impact from a large meteorite may have been responsible for the mass extinction marking the end of the Cambrian Period and start of the Ordovician Period. Impact craters dating to the Ordovician Period have been identified in Australia . See also Archean; Cenozoic Era; Cretaceous Period; Dating methods; Devonian Period; Eocene Epoch; Evolution, evidence of; Fossils and fossilization; Historical geology; Holocene Epoch; Jurassic Period; Mesozoic Era; Miocene Epoch; Mississippian Period; Oligocene Epoch; Paleocene Epoch; Pennsylvanian Period; Phanerozoic Eon; Pleistocene Epoch; Pliocene Epoch; Proterozoic Era; Quaternary Period; Tertiary Period; Triassic Period Cite this article Oxford Dictionary of Rhymes © Oxford Dictionary of Rhymes 2007, originally published by Oxford University Press 2007.

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MLA Geological History - Devonian and Silurian Devonian and Silurian "The Age of Fishes" CLIMATE AND CONTINENTS During the Devonian Period, North America and Europe were formed together to make the supercontinent Euramerica which caused the formation of the Appalachian Mountains. South America, Africa, Antarctica, India and Australia formed Gondwana. Both large land masses were formed on the equator. The two continents moved toward each other throughout the Devonian Period. The waterway between the two continents covered a subduction zone. A subduction zone is an area where one plate is moving underneath the other. The two continents eventually formed the supercontinent Pangea. Laying so close to the equator meant that the climate of the Devonian was warm. The warm temperatures made life on land particularly good for the plants. They developed vascular tissues to carry water and food through the leaves. Ferns and the first trees began to cover the land when plants started to move further inland. THE AGE OF FISHES The Devonian Period is famous for the thousands of species of fish that developed in Devonian seas.They had no jaws and the support structure was made of cartilage.

This material doesn’t fossilize well, so the earliest fossils were of fish whose outside skin was protected by scales and plates made of boney tissue. These fish were called Ostracoderms. FISH WITH JAWS The next development was the fish with jaws, gills and paired fins. The Placoderms were the first fish to have all three of these characteristics. The largest of the Placoderms was the Dunkleosteus. It was a huge predator in the Devonian seas. It could be as long as 10 meters. Instead of teeth, it had large boney plates that stuck down in the front of its mouth opening. The powerful jaws were deadly to other fish, sharks and even other Dunkleosteus. There were many more interesting fish and other animals that developed duing this period. MASS EXTINCTION ENDS THE DEVONIAN PERIOD Species had begun to branch out and include both land and water habitats. The Devonian Period ended with a mass extinction. The Devonian extinction hurt the water habits much more than those on land. The sponges and corals were the most affected. No major reef building happened again for thousands of years.

SILURIAN TIME PERIOD 443 million years ago CLIMATE AND CONTINENTS The Silurian witnessed a relative stabilization of the earth's general climate which followed the harsh conditions the earth saw in earlier periods such as the Devonian. One change was the melting of the glaciers which led to the substantial rise of the sea levels. The Silurian world consisted of a north polar ocean and a south polar super continent which was called Gondwana with a ring of about six continents. A large portion of the Rodinian landmass had separated and those fragments migrated toward the equatorial region. Most of these fragments were eventually assembled by a series of plate collisions into the super-continents of Laurussia and Laurasia. PLANTS AND ANIMALS The Silurian Age saw plants and animals emerge on land. But first, there was regrouping from following the climax of Ordovician period. Fish also became diversifying and extending there feeding options further than vacuuming off the sea bed. Coral reefs made their first appearance during this time and marked the rapid evolution of jaw-less fish as well as the first freshwater fish.

STRATIGRAPHY Silurian's stratigraphy is subdivided into four which is from oldest to youngest. It contains the Llandovery, the Wenlock, the Ludlow, and the Pridoli. Each of these "epochs" is distinguished from the others by the appearance of new species of graptolites. Graptolites are a group of extinct aquatic animals that put in their first appeared in the Cambrien period. 425.jpg (129955 bytes) The Virtual Siluiran Reef -- Silurian Period Britain Murchison, 1859 The Silurian can be defined as a period of geologic time between 408 and 438 million years ago that was preceded by the Ordovician Period and followed by the Devonian Period. The term Silurian comes from Silures, the name of a tribe of people that lived along the border of England and Wales before the time of the Romans. In the early 1800s, British geologists recognized rocks in this area that contained a distinctive assemblage of fossils, different from the fossils in both underlying (or older) strata and overlying (or younger) strata.

"Silurian" was applied to the period of time represented by this fossil assemblage. Silurian fossils, identical to those in Britain, were subsequently discovered in many other regions of the world, including the Great Lakes region of North America. Pictures on the left show Silurian fossils from Britain, and pictures on the right show Silurian fossils from Wisconsin. The pictures are arranged to show the close similarity in marine faunas of these areas. The Silurian world was vastly different in many ways than the world of today. The shapes and distribution of the continents was not the same as now, and shallow seas covered much of the continental areas. For example, the equator passed through North America, and a nearly continuous inland sea stretched between New York and Nevada. Although the Silurian seas were populated by a variety of marine life, the land was inhabited only by a few types of small plants and tiny bugs. Wisconsin Steve Stone Coral Reef Foundation Steve Stone Coral Reef Foundation Geologic Time Geologic History of Reef Construction Bacteria. They were the first life forms on Earth and have managed to exploit virtually every environment on the planet. We find them deep underground in oil pools and even within solid rock.

They occur in the deepest parts of the ocean and high up in the atmosphere. They are incredibly important as decomposers and as mutualistic "partners" in many symbiotic relationships. The cyanobacteria are important photosynthesizers that contribute free oxygen to the atmosphere. In this essential process, they are part of a trinity of O2-producers which includes the various species of marine algae and the land plants. They were also the very first reef-builders on Earth. Stromatolite Reef (exposed at low tide in Shark Bay, Australia) Evidence of ancient cyanobacterial growth has been found in rocks as old as 3.5 billion years. Known as stromatolites, these organosedimentary structures comprised the bulk of the fossil record during the Archean Eon and most of the Proterozoic Eon. Vast reefs were produced by the actions of cyanobacteria who were joined by the red algae (Rhodophyta), brown algae (Phaeophyta), and green algae (Chlorophyta) during the Proterozoic.

These stupendous reef-building projects were curtailed during the Cambrian Period by the emergence of a host of "grazing" invertebrates which took advantage of the extensive bacterial and algal mats. Consequently, although stromatolites are still being produced today, they are nowhere near as abundant as they once were. Cambrian Period The Cambrian Period also witnessed the rise of the first skeletal reef-building organisms on Earth, the Archeocyathids. Unfortunately, their time on Earth would be brief. The entire phylum, consisting of 16 families and some 80 genera, disappeared from the fossil record just prior to the end of the Cambrian Period. But during that relatively short period of geologic time, these primitive "cup animals" constructed some large and impressive reefs, usually in association with stromatolites and sponges. For the sponges also make their appearance during the Cambrian Period. Significantly for our story, this period of Earth's history also witnessed the rise of the massive, colonial stromatoporoid sponges.

This group of formidable reef-builders would prove to be far more successful than the Archeocyathids, persisting and surviving in the shallow seas of our planet well into the Tertiary Period. Thriving in the warm waters of the early Paleozoic seas, the stromatoporoids will join a new group of reef-builders during the Ordovician Period. Solitary Rugose Corals (showing the classic "horn-shaped" structure of these Ordovician species) Ordovician Period During the middle part of the Ordovician Period, a major marine transgression resulted in widespread inundation of the continental cratons. As a result of this increase in the shallow marine environment, benthic organisms proliferated. Among these were three great reef-building groups and a significant contributor to the reefs being constructed at this time. The stromatoporoid sponges comprise one of the reef-building groups, but the other two are corals. Known as the tabulate corals and the rugose corals, these novel and revolutionary forms of life would become the premier reef-builders of the Paleozoic.

It is this trinity of stromatoporoid sponges, tabulate corals, and rugose corals that would dominate reef-building during the Ordovician, Silurian, and Devonian Periods. They would be assisted in this effort by the trepostome bryozoans. These "stony bryozoans" constructed dense carbonate structures which contributed significantly to the coral reefs, helping to "glue" them together into a compact mass. The trepostomes flourished during the Ordovician but then steadily declined during the Silurian and Devonian Periods. Silurian Period The tabulate corals were the principal reef-building corals during the Silurian Period. Their place was gradually taken by the rugose corals during the following Devonian Period. But both groups coexisted during this period and would continue to do so to the very end. Both groups are important in that the tabulate corals were the world's first true coral reef builders and the rugose corals literally set the stage for modern-day coral reef systems.

Tabulate Coral (Favosites species), Devonian Period Devonian Period Near the end of the Devonian Period, a mass extinction event occurred in the marine ecosystem which resulted in a global collapse of the world's reef communities. The massive reef structures of the Silurian and Devonian Periods virtually disappeared, being replaced by smaller "patch" reefs dominated by sea lilies, bryozoans, brachiopods, and calcareous algae. Of course, "life will find a way" and this unoccupied niche in the shallow marine environment could not remain vacant for long. By the middle of the Mississippian Period, another group of important reef-building tabulate corals had emerged to fill the gap. The chaetetids, as they are called, became the dominant constructors of reefs during the Pennsylvanian Period. Their populations then declined somewhat, but they somehow managed to survive the great Permian extinction event. This catastrophic die-off wiped out over 90% of the life forms on Earth. The slate was nearly wiped clean and the world would never be the same again. A new and vibrant group of reef-building corals would appear and come to dominate the reef systems of the world.

Known as the scleractinians, this group of highly successful corals made their appearance during the Triassic Period, shortly after the demise of the tabulate and rugose corals. The scleractinians are still with us today. The huge coral reefs that flourish in the tropical waters of present-day Earth are a testament to their success. Fossil Bryozoans (including both lace-like and branching forms) Jurassic Period Their history was one of success, but only when water conditions were nearly perfect. During the Jurassic Period, a group of unusual reef-building clams known as the rudistids actually came to dominate some portions of the shallow epeiric seas surrounding the land masses. In highly saline waters, rudistids frequently out-competed the scleractinians. But the corals would turn out to be the ultimate winners. The rudistid clams vanished from the fossil record at the end of the Cretaceous Period. Cretaceous Period The Cretaceous Period witnessed the rise of another Cnidarian reef-building group that survived the Cretaceous extinction event and went on to dominate the warm Tertiary seas that followed.

The colonial reef-building hydrozoans known as the milleporids joined the scleractinian corals in constructing massive reefs during this period of time. Yet another group of Cnidarians appeared during the Cretaceous Period, survived the die-off, and then joined the milleporids and scleractinians in constructing reefs during the following Tertiary Period. The coenothecalians secreted massive CaCO3 skeletons which augmented and strengthened the structures produced by the other reef-building groups. The Modern Era The coral reefs of today are dominated by scleractinian corals, although some coenothecalians like the Blue Coral (Heliopora coerulea) are locally quite abundant. But again, only in waters where temperature, chemistry, and turbidity levels are nearly perfect do we find healthy, thriving coral. In less than perfect conditions, coral is easily stressed and can be out-competed by other benthic sessile, encrusting organisms. Red coralline algae in particular is notorious for colonizing and "taking over" coral reef substrate when water conditions are compromised.

Question: Which geological period followed the 'Devonian Period' but preceded the 'Ordovician'?
Answer: SILURIAN