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Geologic Time Scale
Transcript of Geologic Time Scale
The Precambrian Period can be divided in the times: Hadean, Archean and Proterozoic and is considered to be the beginning of the Geologic time scale; the origin of earth.
The Mesozoic Era is divided into three time periods: The Triassic, The Jurassic, and the Creaceous. Mesozoic means "middle animals". This is a time where Dinosaurs would roam the earth. It is also a time when the terrestrial vegetation underwent great change.
The Cenozoic Era began about 65 million years ago after the extinction of the dinosaurs, it continue through the present. It is divided into three time periods: Paleogene, Neogene and Quaternary. But generally, for simplicity purposes, can be divided into Tertiary and Quaternary. It is the age of mammals, where whales take over the oceans and saber-tooth tigers share the land with elephants and giant sloths...and where humans finally appear.
The Paleozoic Era lasted about 325 million years, from about 570 millions years ago to approximately 245 million years ago. It is divided into seven geologic time periods: Cambrian, Ordovician, Silurian, Devonian Mississippian, Pennsylvanian, and Permian
Early Earth (In Theory)
Approximately 4.6 billion years ago Earth was formed. However, it is important to note that Earth did not look like it does today. Rock and Ice that swirled around the young Sun collided and merged, sticking together through the simple process of attraction. As a result, planets began to form over a process of billions of years, in which one specifically being
In the hectic scene of colliding particles Earth was impacted by a large body believed to be as big as Mars, this body was mostly engulfed by the magma ocean it created when it hit Earth, but debris soared from planet and recollected in Earth's orbit to create the moon. For the next 700 million years the Earth would take its time to cool, being a vast wasteland where solid rock would drift over magma bodies like ice floats in the Arctic. Welcome to the Hadean Era...
During the early part of of the Hadean , Earth's surface was believed to be incredibly unstable. Molten rock was brought to the surface through convection currents causing cooling rock to descend into the magmatic oceans. The heaviest of elements, such as iron, descended deep into the earth to create the core; this all while lighter elements, such as silicon, floated to form the crust. With this being said, it is hard to determine when the first outer crust formed due to it being nearly all destroyed through subduction caused by the movements of tectonic plates...but it is believed by scientists that the existence of very few grains of zircon dated to approximately 4.4 billion years ago confirm the presence of stable continents.
Earth's primordial atmosphere had been lost when the moon was created,, however, degassing from the magma ocean and additional material that came from colliding comets produced Earth's water oceans and atmosphere. Earth's atmosphere was mostly composed of methane, carbon dioxide, nitrogen, ammonia and water vapor and in which resembled that of Saturn's moon, Titan. The Earth's oceans were most likely short lived due to space rubble bombarding the planet throughout the Hadean, larger impacts would have boiled oceans away and force the process of cooling and condensation to commence again.
At about 3.8 billion years ago, the impacts of space rubble lessened, and liquid water was able to persist to create huge bodies,: oceans.
The Archean occurred 3800 million years ago and lasted until 2500 million years ago. This was a time when diverse microbial life began to appear in the primordial oceans. The continental shields also began to develop from volcanic activity, and the reduction of the anaerobic atmosphere enabled anaerobic microbes to develop. Plate tectonics began to follow a regime of continental drift to that of the Proterozoic and later. Specifically, the Cyanobacteria (blue-green algae) began to produce OXYGEN as a result of a metabolic by product.
The microorganisms of this period may have used methane or hydrogen rather than oxygen in their metabolism. That is why they are referred to as "anaerobic" which means "non oxygen using. Life on Earth was most likely created when the world went through a period of chemical evolution: simple organic molecules gradually aggregated together to form larger and more complex macro-molecules. The Archean showed that not all single celled organisms were solitary. Blue-green algae formed stromatolites, which are the basic structure of large mats. Stromatolites are the world's oldest fossils, they are significant in the sense that they allow scientists to dive deep in to early Earth. They represent the emergence of life, and a single Stromatolite encodes biological activity, possibly spanning thousands of years.
The Archean was also responsible for the period of maximum continent formation. In fact, 70% of the continental landmasses date from this period. 3 billion years ago, the continent Ur formed, In the early part of its existence, it was most likely the only continent on Earth, however it is suggested that it was smaller than Australia today.
The Proterzoic is the period of Earth's history that began 2. billion years ago and lasted until 542 million years ago. It is subdvided into three eras: The Paleoproterozoic, Mesoroterzic, and Neoproterzoic. It is a very exciting eon overall because many exciting events take place. This includes stable continents first appearing and beginning to accrete, and the presenting of an abundant amount of fossils of living organisms.
During the earlier Prtoerzoic, stromatolites began to increase in diversity. They flourished in shallow waters throughout the world. But later on (700 million years ago) they began to decline in abundance and diversity. It is a bit unclear as to why this occurred, but a popular theory suggests that herbivorous eukaryotes evolved around this time and began feeding excessively on the stromatolites.
2.2 billion years ago, a pollution crisis hit Earth, this was a first for the world. By examining several pieces of evidence, scientists were able to see the presence of iron oxides in fossil soils, called paleosols, the appearance of "red beds" containing metal oxides, and others. These in which point to a generally rapid increase in levels of oxygen in the atmosphere. Bearing in mind,, atmospheric oxygen levels in the Archean had been less than 1% than that of present levels, however, by about 1.8 billion ears ago, oxygen levels were greater than 15% of present levels and rising. Oxygen was a powerful degrader of organic compounds, in which killed many organisms. Organisms had to evolve biochemical methods for being unharmed b oxygen. One of the main methods to such was oxidative respiration, which had the advantage of producing large amounts of energy for the cell, and is now found in most eukaryotes.
The oxygen was coming from cyanobacteria, which were photosynthetic organism that produced oxygen as a byproduct. They had existed 3.5 billion years ago, but had began becoming widespread, being responsible for the rise in atmospheric oxygen.
The Cambrian period produced the most intense burst of evolution ever known. It saw an incredible diversity of life emerge, these in which included major animal groups that are alive today, specifically chordates (vertebrates belong to this group).
The climate of the Cambrian period is suggest to have been cold in its earlier parts, as the glaciers of late Proterozoic Eon receded. Tectonic evidence theorizes that the single supercontinent, called Rodinia, broke apart and by mid Cambrian, had become two continents. One of thee was Gondwana, which was located near the South Pole. It held together much of the land that later formed to be AFrica, Australia, South America, Antartica and parts of Asia. The other continent was Laurentia, and was more near the equator. It was composed of landmasses that currently make up most of North America and part of Europe. Shallow sea environments and increased coastal area and flooding were due to glacial retreat.
At this time, there was no life existing on land, and all life was aquatic. In very early Cambrian, microbial "carpets" were present on the sea floor, multicellular life forms that had evolved in the late Proterzoic grazed on the microbes. Furthermore, these multicellular organisms were the first to show evidence of a bilateral body plan. They were near-microscopic "worms", and they began to borrow, mixing and oxygenating the mud of the ocean floor. Also at this time, dissolved oxygen was increasing in the water due to the presence of cyanobacteria. The first animals to develop calcium carbonate exoskeletons built coral reefs.
In the middle of the Cambrian Period, there was an extinction event. Excessively, the reef-building organisms diedd out. This would include the most primitive trilobites. Among many theories, the most common suggest that the extinction was due to a temporary depletion of oxygen caused by and upwelling of cooler water from deep ocean areas. Scientists believe that the increase in available ecological niches set the stage for the sudden radiation in life forms.
The Ordovician period lasted almost 45 million years, beginning 4888.3 million years ago and ending 443.7 million years ago. This was a period where the north of the tropics was almost entirely ocean, and most of the word's landmasses was collected into the southern supercontinent Gondwana. Over the Ordovician period, Gondwana shifted towards the South Pole and much of it was submerged underwater.
This period is also best known for its varying marine invertebrates, including graptolites, trilobites, brachiopods, and the early vertebrates - conodonts. It is believed that a typical marine community would have consisted of these animals, along with red and green algae, primitive fish, cephalopods, corals, crinoids, and gastropods. Interestingly, tetrahedral spores that are similar to those of primitive land plants have been discovered, suggesting plants may have started to move onto land at this time.
The earth was a milder climate from the lower to middle Ordovician. The weather was fairly warm and the atmosphere was moist. But when Gondwana finally settled on the South Pole during the upper Ordoician, huge glaciers formed, causing seas to drain and sea levels to decrease. This characterized the extinction that occurred at the end of the Ordovician, where 60% of all marine invertebrate genera went extinct, along with 25% of all invertebrate families went extinct.
Extending from 443.7 million years ago to 416 million years ago, the Silurian was a tie when the Earth underwent significant changes, in which effected the environment and life within it. Glacial formation melted and as a result there was a substantial rise in the levels of the major seas. There was a relative stabilization of the Earth's general climate, which ended the previous pattern of erratic climatic fluctuations. More so, coral reefs began to appear and fishes began to evolve! The time period marked the wide spread of jaw-less fish, but most importantly marked the significant appearances of both the first known freshwater fish as well as the first fish with jaws.
Clear evidence of life on land occurred in Silurian, indeed, there is possibility that plants and animals first moved onto the land in the Ordovician, but fossils of terrestrial life are fragmentary and hard to interpret. Silurian strata have provided scientists with ascomyycete fossils, as well as remains of the first arachnids and centipedes. Another incredible event that occurred in Silurian is the evolution of vascular plants.
During Silurian, there were major orogenic events in eastern North America and in Northwestern Europe, which resulted in the formation of the mountain chains there. The ocean basins between the regions closed substantially. There was not much for dramatic tectonic activity, but the Silurian period underwent gradual continental changes that would be the foundation for greater global consequences. the rise in sea levels would create many new marine habitats, providing the framework for huge biological events in the evolution of life.
In the seas of Devonian, there was a domination of brachiopods that built large reefs in the shallow waters. In the lower Devonian, ammonoids appeared, which left behind large limestone deposits from their shells. There was a rapid diversification in fish. Benthic, jawless, and armored fish were common in the lower Devonian. By middle Devonian, pacoderms, which were the first jaw fished, appeared. All in which would have grown to be very large in size and were fearsome predators. Before the end of the Devonian, there was the rise of the first sacropterygians, the lobe-finned fish, which eventually produced the first tetrapods.
Colonization of the land was beginning to flourish. Early terrestrial vegetation had begun to spread. The plants would have not had roots or leaves, and many most likely contained no vascular tissue at all all. By late Devonian, lycophytes, sphenophytes, ferns, and progymnosperms had evolved. They would have had true roots and leaves, and would have grown quite tall. There was a rapid appearance of so many plant groups and growth forms during the late Devonian that it has been dubbed the "Devonian Explosion". Along with the diversification in terrestrial vegestation structure, followed a diversification of the arthropods.
During Devonian, the word's landmasses was collected into two super continents (Gondwana and Euramerica). They had lay relatively close to one another in a single hemisphere. They were surrounded on all sides by subduction zones and with the development of the subduction zone between the two super continents, a major collision was set in motion. This coming together would form the single world-continent Pangea. Near the end of the Devonian, a mass extinction occurred. It is believed that glaciation and the lowering of global sea level contributed to the crisis. However, meteorites have also been pointed to in blame of the mass extinction. Whatever the cause may have been, it was around this time that the first vertebrates moved onto land.
Carboniferous: Pennsylvanian and Mississippian
The Carboniferous Period is commonly broken up into two parts: The Lower Carboniferous (AKA Mississippian) and the Upper Carboniferous (AKA Pennsylvanian). Overall, this period takes place from 360 million years ago to 290 million years ago. With the split between Mississippian and Pennsylvanian being 310 million years ago. The reason for the division, was so that it could be distinguised the coal-bearing layer of the Pennsylvanian from the mostly limestone Mississippian.
In Pennsylvanian, there was ideal condition for the formation of coal. Overall it is seen that several major biological, geological, and climatic events occurred during this time. Biologically, there was the evolutionairy innovation: the amniote egg. This allowed for the further movement inland by certain tetrapods. There was now the ability to la eggs on land without fear of desiccation. Geologically, in Mississippian, the collision of Laurasia into Gondwana resulted in the production of the Appalachian Mountain belt of eastern North America and the Hercynian Mountains in the United Kingdom. Furthermore, theree was a collision of Siberia and Eastern Europe, which created the Ural Mountains of Russia. Climatically, mild temperatures occurred during the Carboniferous, evidence provides support, showing that there was a decrease in lycopods and large insects and an increase in the amount of tree ferns.
The Mississippian environment of North America had been heavily marine, with seas that covered parts of the continent. Consequently, most Mississippian rocks are limestone, which are made up of the remains of crinoids, lime-encrusted green algae, or calcium carbonate shaped by waves. In contrast, the Penssylvanian environment was alternately terrestrial and marine, with the transgression and regression of the seas cause by glaciation. In combination of these environmental conditions and the abundant amounts of plant material, there was the allowance for the formation of coal.
The Permian period occurred between 299 to 251 million years ago. At the end of Permian period there is recognition of the largest mass extinction recorded in the history of life on Earth. The coming together of supercontinent Pangea proved to set the stage for severe extremes of climate and environment due to its size. For the South was cold and arid, with most of the region frozen under ice caps, where as the North was suffering from increasingly intense heat and great seasonal fluctuations between wet and dry conditions. It was at the advantage of early reptiles who were able to make the most on the new environment. They were shielded by thicker, moisture-retaining skins,. They were cold blooded, and had to find ways to deal with big daily variations in temperature. Eventually mammal-like reptiles known as therapsids found an internal solution to keeping warm. This is where scientists believe they evolved to become warm-blooded, able to conserve heat generated through the breakdown of food. The therefore became the more dominant land animals of the late Permian, as they were able to survive the harshest of interior regions.
Furthermore, therapsids began to evolve rapidly into different forms, this included dinosaur-like fanged flesh-eaters to plodding herbivores. Some species even reached a great size, weighing more than a ton. Most interestingly though, was the emergence of the smaller varieties, warm-blooded and covered in insulating hair...where mammals would arise. In the seas, bony fishes wish fan-shaped fins and thick, heavy scales, dominated. There were large reef communities that were home to squidlike nautiloids.
But alas, there was a massive loss of life. 251 million years ago it is estimated that 90% of all marine species and 70% of all land animals were wiped out. There are many theories that explain this mass extinction, some scientists are under the impression that there was a series of volcanic eruptions that pumped so much debris into the atmosphere the sun was blocked out, causing a huge drop in temperature. This prevented plant photosynthesis, which as a result, caused food chains to collapse. However the case, new animals and plants were evolving to fill the void...DINOSAURS.
This was a time of transition, lasting from 248 to 206 million years ago. Pangea existed and altered the global climate and ocean circulation. It is a time following a mass extinction, where survivors of the past begin to spread and recolonize.
At the beginning of Triassic, no dinosaurs existed, there were many amphibians and some reptiles and dicynodonts. Corals appeared and ammonites recovered. Seed plants were also dominating the land' in the Northern hemisphere, conifers were abundant. In the South, Glossopteris were dominant. In late Triassic, the first true mammals appeared. These primitive mammals were tiny and are though to have been nocturnal. It was an awesome moment, animals that are recognizable began to truly appear, such as turtles, frogs, salamanders, and lizards appeared.
Climatically, Triassic appeared to be hot and dry, with strong seasonality. Pangaea decreased the amount of sholine, formed mountains, and gave the interior of the supercontinent a dry and desert-like terrain. Even the polar regions were moist and temperate.
Unfortunately, the Trassic period ended with a mass extinction accompanied by huge volcanic eruptions that are dated to have occurred about 208 - 213 million years ago. The supercontinent Pangaea was breaking apart. 35% of all animal families died out as well, including all labryinthodont amphibians, conodonts, and all marine reptiles except ichthyosaurs. Most of the early, primitive dinosaurs became extinct, but the more adaptive dinosaurs evolved in the Jurassic.
It is unclear what caused the Triassic extinction, some possibilities are global cooling or asteroid impact. Nevertheless, the extinction allowed the dinosaurs to expand into many niches that were unoccupied. They would become more dominant and abundant.
The Jurassic Period was between 199.6 to 15.5 million years ago It was filled with huge plant-eating dinosaurs that fed on lush fers and palm-like cycads and bennettitaleans. There was also the presence of carnivores stalking the great herbivores. There were oceans full of fish, squid and coiled ammonites. Pterosaurs were the firs birds. Dinosaurs dominated the land fauna, with the largest dinosaur being the sauropods, such as the Diplodocus, Brachiosaurus and Apatosaurus. Other herbivores included stegosaurs. The Predatory dinosaurs of Jurassic included carnosaurs, such as coelurosaurs, and ceratosaurs such as Dilophosaurus.
Land plants were abundant in the Jurassic, there were no palms or any other flowering plants. Instead, there were many ferns, ginkgoes, bennettitaleans, and true cycads.
There was no polar ice during the Jurassic, thus the sea levels were high. The climate was warm and when Pangaea began to break up, there was vast flooded areas, temperate and subtropical forests, and coral reefs. There was a minor mass extinction toward the end of the Jurassic period, much of the stegosaurid and enormous sauropod dinosaurs died out. These along with many genera of ammonoids, marine reptiles, and bivalves. The reasoning for this extinction remains unclear.
Lasting from 144 million years ago to 65 million years ago, Cretaceous was the heyday for the dinosaurs. Huge carnivores had started to appear. These included the famous T-rex and Giganotosaurus, along with the Triceratops and many, many others. Mammals were abundant and flowered plants developed, radically changing the landscape.
In the first part of the Cretaceous, the climate proved to be warm, seasonality was low, and global sea levels were high. B the end of Cretaceous severe climate changes occurred, and this resulted in lowere seal levels and high volcanic activity.
The Creataceous period ended abruptly, about 65 million years ago, the dinosaurs were wiped out, with an exception to the birds. Along with the extinction of dinosaurs, was the extinction of pterosaurs, ichthyosaurs, ammonite, mosaaurs, plesiosaurs, and half of all invertebrate marine organisms. This event is believed to have occurred due toan asteroid impact, but there are many other theories that include high volcanism, climate changes due to continental drift, and the effects of disease. In conclusion, the Age of Reptiles came to an end, The age of Mammals was now able to begin.
Occurring between 66 million and lasting until 1.8 millions years ago, Tertiary is marker for the rise of the mammals. The beginning of the Tertiary Period was understood to be very warm and moist. A majority of the earth was tropical or sub-tropical and PAlm trees grew as far north as Greenland. By the middle of the tertiary, the climate began to cool. By the end of of the Tertiary period, and ice age began to occur.
The plants of the Tertiary Period are very similar to those that exist on Earth today. The warm climate of the beginning of the period favored dense forests. As the climate cooled, woodlands and grasslands became more abundant. These in which supported large herds of grazing animals.
The extinction of dinosaurs, large reptiles and many other species that had occurred in the Cenozoic period left room for new animals to develop. Therefore, mammals became dominant. Hominids were the first of Human ancestors and appeared during Tertiary (in the Pliocene Epoch). Birds also did very well during the Tertiary Period, and many exist today still. Boney fish and sharks developed into new species and flowering plants that were now present meant nectar for insects. But the tertiary period ended with an Ice Age, as huge glaciers formed at the poles when the climate cooled.
The Quaternary Period accounts for the most recent 2.6 million years of Earth's history. Glaciers had advanced from the Poles and then retreated, which carved and molded the land. Sea levels fluctuated with each period of freezing and thawing. Some mammals got massive, grew furry coats, and then disappeared. Humans were also known to evelove to their modern form, affecting everything; including the climate.
At the beginning, the continents were just about where they are today. Due to slight shifts, 800,000 years ago, a cyclical pattern emerged and ice ages would last about 100,000 years followed by warmer inter-glacials of 10,000 to 15,000 years each, with the last ice age having ended about 10,000 years ago. As sea levels rose fast, the continents bear their present-day outline.
The coldest of Quaternary saw mammals like mammoths, rhinos, bison, and oxen. But when the climate began to warm about 10,000 years ago, most of these mammals went extinct. Only some of the smaller ones (still impressively large) such as Africa's elephants, rhinoceroses, and hippopotamuses remained. At the end of the ice age, modern humans were rapidly spreading around the globe. They had first appeared in Africa at the start of the period, but as time moved on the hominid line evolved bigger brains and higher intelligence. They evolved from Africa about 190,000 years ago and dispersed to Europe and Asion and then on to Australia and the Americas.
So, from 4.6 billion years ago to Present day, we see a huge progression that is mind bending to comprehend the amount of time it took to get here. Humans now dominate, and everyday animals are becoming extinct. The Earth is warming, the poles are shifting, and continents continue to shift. Incredible.
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Encyclopedia of Earth. Eds. Cutler J. Cleveland (Washington, D.C.: Environmental Information Coalition, National Council for Science and the Environment). [First published in the Encyclopedia of Earth August 23, 2008; Last revised Date February 11, 2013; Retrieved June 17, 2013 <http://www.eoearth.org/article/Cenozoic>
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University of California, Museum of Paleontology. http://prezi.com/8gd8bciz2hr8/edit/#37_19503260 Copyright 1994-2013 by the Regents of the University of California, all rights reserved.