Eon era period

What is eon era period and age epoch? Epochs are the smallest divisions. Many epochs make up a period, many periods make up an era, and many eras make up an eon. In defining the boundaries between major divisions, we often use markers, like the dinosaur extinction or the appearance of certain organisms.

Eon era period. Organization. In the geologic time scale, the youngest ages are on the top and the oldest on the bottom. The time scale is based upon relative times, therefore there aren’t any specific times listed with each era. The timescale is divided into eons, each eon into eras, each era into periods, and each period into epochs.

Phanerozoic Eon. The Phanerozoic Eon is divided into three eras, the Paleozoic, Mesozoic and Cenozoic eras. These were named for the kinds of fossils that were present. The Cenozoic is the youngest era and the name means “new life”. This is because the fossils are similar to animals and plants that are common today.

EON: ERA: PERIOD: EPOCH: MILLIONS OF YRS AGO: MAJOR BIOLOGICAL EVENTS: P H A N E R O Z O I C: C E N O Z O I C: Quaternary: Holocene.01. Rise of civilization and agriculture. Extinction of large mammals in northern hemisphere. Pleistocene: 1.8: Modern humans appear. Four major glaciations cause rapid shifts in ecological communities. Tertiary ...Each eon is then split into different eras. For example, the Phanerozoic eon is made up of, from oldest to youngest, the Paleozoic, Mesozoic, and Cenozoic eras. Eras are split into periods. The Cenozoic era includes, from oldest to youngest, the Paleogene, Neogene, and Quaternary periods. Finally, the periods are divided into epochs. The ...Classifying time To make geologic time easier to comprehend, geologists divided the 4.6 billion years of Earth’s history into units of time called eons. Then they further divided the eons into two or more eras, eras into two or more periods, periods into two or more epochs, and epochs into two or more ages.The Phanerozoic eon—the past 540 Ma of Earth’s history—is divided into three eras: the Paleozoic (“early life”), the Mesozoic (“middle life”), and the Cenozoic (“new life”), and each of these is divided into a number of periods (Figure 8.1.3). Most of the organisms that we share Earth with evolved at6 days ago ... The meaning of EON is an immeasurably or indefinitely long period of time : age ... era. the Archean eon. b. : a unit of geologic time equal to ...Sep 11, 2013 · EON ERA PERIOD EPOCH; Phanerozoic 542 Ma to present: Cenozoic 65 Ma to present: Quaternary 2.6 Ma to present: Holocene 11,700 years ago to present: Pleistocene: Tertiary 65 to 2 Ma: Pliocene 5.3 to 2.6 Ma: Miocene 23.0 to 5.3 Ma: Oligocene 33.9 to 23.0 Ma: Eocene 58.7 to 33.9 Ma: Paleocene 65 to 58.7 Ma: Mesozoic 251 to 65 Ma: Cretaceous 145 to ... The Hadean (IPA: / h eɪ ˈ d iː ə n, ˈ h eɪ d i ə n / hay-DEE-ən, HAY-dee-ən) [] is the first and oldest of the four known geologic eons of Earth's history.It started with the planet's formation about 4.54 Bya, now defined as (4567.30 ± 0.16) Mya set by the age of the oldest solid material in the Solar System found in some meteorites about 4.567 billion years old. The Precambrian encompasses the Archean and Proterozoic eons, which are formal geologic intervals that lasted from 4 billion to about 541 million years ago, and the Hadean Eon, which is an informal interval spanning from 4.6 billion to 4 billion years ago. The Precambrian represents more than 80 percent of the total geologic record.

Study with Quizlet and memorize flashcards containing terms like Explain how fossils are formed and why they are not equally prevalent in all areas., 8B. Define the terms eon, era, period, and epoch and specify modern humans' place in geologic time., 8C. Compare relative age and relative dating methods with numerical age and absolute dating methods. and more.Figure 8.3.1 8.3. 1: Geologic Time Scale with ages shown. The Hadean Eon, named after the Greek god and ruler of the underworld Hades, is the oldest eon and dates from 4.5–4.0 billion years ago. This time represents Earth’s earliest history, during which the planet was characterized by a partially molten surface, volcanism, and asteroid ...The meaning of EON is an immeasurably or indefinitely long period of time : age. How to use eon in a sentence. an immeasurably or indefinitely long period of time : age; a very large division of geologic time usually longer than an era… eon - era - period - epoch. Boundaries between intervals of the geological time scale are determined by. major events in the Earth's history, such as major extinctions.The Precambrian was originally defined as the era that predated the emergence of life in the Cambrian Period. It is now known, however, that life on Earth began by the early Archean and that fossilized organisms became more and more abundant throughout Precambrian time. The two major subdivisions of the last part of the Precambrian are …The Paleozoic Era. The Cambrian Period: Following the Precambrian mass extinction, there was an explosion of new kinds of organisms in the Cambrian Period (544–505 million years ago).Many types of primitive animals called sponges evolved. Small ocean invertebrates called trilobites became abundant.. Two representatives of more than fifty modern animal …

22-Feb-2022 ... 1. Eon: A geological time unit that represents the longest period of time in the geologic time scale, typically lasting billions of years.Feb 28, 2020 · Eon geologi terbaru adalah Fanerozoikum, yang dimulai sekitar 540 juta tahun yang lalu. Eon ini sangat berbeda dari tiga eon sebelumnya—Hadean, Archean, dan Proterozoic—yang kadang-kadang dikenal sebagai era Prakambrium. Selama periode Kambrium—bagian paling awal dari Fanerozoikum—organisme kompleks pertama muncul. Railroads struggled during the Great Depression, as did the rest of the nation. Read about railroads of the Depression era and the New Deal. Advertisement The period between 1930 and 1945 was a time of contrast and change. The railroad indu...The period is the basic unit of geological time in which a single type of rock system is formed. Two or more periods comprise a geological Era. Two or more Eras form an Eon, the largest division of geologic time. Some periods are divided into epochs. The major periods in the geologic history of the Earth are (mya=million years ago):An eon can be considered the same as a kalpa in Sanskrit. Eon is also the longest period of time as per geology, which explains why an eon is subdivided into eras. An era is another unit of measuring a specific period of time, basically in historical contexts. An era denotes a long period of time, but not longer than an eon.The Chinese tributary system was a largely-symbolic Confucian world order, with its basis in trade and philosophical relations between foreign states and various Chinese dynasties. The diplomatic system in East Asia was …

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Aug 23, 2023 · Precambrian, period of time extending from about 4.6 billion years ago (the point at which Earth began to form) to the beginning of the Cambrian Period, 541 million years ago. The Precambrian encompasses the Archean and Proterozoic eons, which are formal geologic intervals that lasted from 4 billion to about 541 million years ago, and the ... The Phanerozoic Eon is divided into Eras: Paleozoic, Mesozoic, and Cenozoic. The divisions among Eras reflect major changes in the fossil record, including the extinction and appearance of new life forms. ... the generally accepted divisions are eon, era, period, epoch, age. In the time scale shown at left, only the two highest levels of this ...First eukaryotes (single-celled algae): 1.4 billion years old. ... originate 3.5 billion years ago. ... HADEAN EON 3,800- No life known. Cooling and solidifying of ...First eukaryotes (single-celled algae): 1.4 billion years old. ... originate 3.5 billion years ago. ... HADEAN EON 3,800- No life known. Cooling and solidifying of ...The well-identified events of this eon were the transition to an oxygenated atmosphere during the Paleoproterozoic; the evolution of eukaryotes; several glaciations, which produced the hypothesized Snowball Earth during the Cryogenian Period in the late Neoproterozoic Era; and the Ediacaran Period (635 to 538.8 Ma) …

B. eon, era, period, epoch Assume that man's recorded history can be stretched back to 4600 years before the present. This is approximately what fraction of geologic time?22-Feb-2022 ... 1. Eon: A geological time unit that represents the longest period of time in the geologic time scale, typically lasting billions of years.The Phanerozoic Eon covers 541 million years and includes three major geological eras: the Paleozoic, Mesozoic and, Cenozoic. Three definitions for Eon are: 1. An indefinitely long period of time ...The early and late phases of this eon may have undergone Snowball Earthperiods ... Started about 541 million years ago and continues to the present is known as the Phanerozoic Eon. This eon can be divided into 3 Eras. These 3 eras are the Paleozoic, Mesozoic, and Cenozoic. Each of these Eras can be subdivided even further into Periods.Eon is an 'immeasurably long period of time' (geologically, it is 1,000 million, or a billion years). · epoch (same origin in Ancient Greek, ...Acrocanthosaurus was a sauropod of spectacular proportions. Learn more about the Acrocanthosaurus, Early Cretaceous dinosaurs, and dinosaurs of all eras. Advertisement ACROCANTHOSAURUS (AK-roh-KANTH-oh-SORE-us) Period: Early Cretaceous Adve...08-May-2001 ... "Eon" also means any span of one billion years. 2nd Order, Erathem, Era, A geologic division including several periods, but smaller than an eon.Standard 8-2.4: Recognize the relationship among the units—era, epoch, and period—into which the geologic time scale is divided. Eons: Longest subdivision; based on the abundance of certain fossils Eras: Next to longest subdivision; marked by major changes in the fossil record Periods: Based on types of life existing at the timeIntervals of geological time are given formal names and grouped into a hierarchy according to their length (in decreasing time intervals):. eon; era; period ...Eon, era, period, epoch. Assume that man's recorded history can be stretched back to 4600 years before the present this is approximately what fraction of geologic time.

The Precambrian eon spans from 4.5 billion years ago when the Earth was formed to 600 million years ago when the first invertebrates appear 8 The Precambrian Eon Hadean era: 4.5 bya - 4 bya...

Eon: 4 total, half a billion years or more Erathem: Era: 10 defined, several hundred million years System: Period: 22 defined, tens to ~one hundred million years Series: Epoch: 34 defined, tens of millions of years Stage: Age: 99 defined, millions of years Chronozone: Chron: subdivision of an age, not used by the ICS timescaleEON: ERA: PERIOD: EPOCH: MILLIONS OF YRS AGO: MAJOR BIOLOGICAL EVENTS: P H A N E R O Z O I C: C E N O Z O I C: Quaternary: Holocene.01. Rise of civilization and agriculture. Extinction of large mammals in northern hemisphere. Pleistocene: 1.8: Modern humans appear. Four major glaciations cause rapid shifts in ecological communities. Tertiary ...Oxygen levels begin at 20% of the atmosphere, and then steadily increase to 27.5%. Carbon dioxide levels begin at ~4,200 ppm and drop to 2,900 ppm in the Middle Devonian, then increasing to ~3,500 ppm by the Period's end. The colonization of land by plants led to the following changes in carbon dioxide and oxygen (Dahl & Arens 2020):. Atmospheric CO2 …The order of the geologic time intervals is Eon, Era, Period, Epoch. What are the longest and the shortest lengths that could be labeled 7 inches to the nearest inch? Longest: 7. ...Era, a very long span of geological time; in formal usage, the second longest portion of geologic time after an eon. Ten eras are recognized by the International Union of Geological Sciences. An era is composed of one or more geological periods. The stratigraphic, or rock, term that corresponds to ‘era’ is ‘erathem.’.What is eon era period and age epoch? Epochs are the smallest divisions. Many epochs make up a period, many periods make up an era, and many eras make up an eon. In defining the boundaries between major divisions, we often use markers, like the dinosaur extinction or the appearance of certain organisms.The geologic time scale (GTS) is a system of chronological dating that relates geological strata (stratigraphy) to time, and is used by geologists, paleontologists, and other Earth scientists to describe the timing and relationships of events that have occurred during Earth's history. Rise of humans, earliest writing in c. 3200 B.C., human ...Mar 15, 2021 · eon = The largest unit of time. era = A unit of time shorter than an eon but longer than a period. period = A unit of time shorter than an era but longer than epoch. epoch = A unit of time shorter than a period but longer than an age. Archean = “Ancient” eon from 4,500 Mya – 2,500 Ma. The Paleoproterozoic Era (also spelled Palaeoproterozoic), spanning the time period from (2.5–1.6 Ga), is the first of the three sub-divisions of the Proterozoic Eon. The Paleoproterozoic is also the longest era of the Earth's geological history.It was during this era that the continents first stabilized. [clarification needed] ...Study with Quizlet and memorize flashcards containing terms like Explain how fossils are formed and why they are not equally prevalent in all areas., 8B. Define the terms eon, era, period, and epoch and specify modern humans' place in geologic time., 8C. Compare relative age and relative dating methods with numerical age and absolute dating methods. and more.

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Jurassic Period, second of three periods of the Mesozoic Era. Extending from 201.3 million to 145 million years ago, the Jurassic was a time of global change in the continents, oceanographic patterns, and biological systems. On land, dinosaurs and flying pterosaurs dominated, and birds made their first appearance.Evolution is the significant process. Geological time scale represents the major eon, era, periods and epoch. It tells us how the earth had been continued wi...Eon, era, period, epoch. Assume that man's recorded history can be stretched back to 4600 years before the present this is approximately what fraction of geologic time.eon era bdy. ages (ma) 1000 1200 1800 2050 2300 1400 1600 2500 2800 3200 3600 4000 541 635 720 period ediacaran cryogenian tonian stenian ectasian calymmian statherian orosirian rhyacian siderian neopro-terozoic mesopro-terozoic paleopro-terozoic neoarchean meso-archean paleo-archean eoarchean hadean 260 280 300 320 340 380 360 400 420 440 460 ... Archeozoic Eon (Archean) 3.9 to 2.5 billion years ago--"Ancient Life" - The first life forms evolve - one celled organisms. Blue-green algae, archaeans, and bacteria appear in the sea. This begins to free oxygen into the atmosphere. Hadean Eon 4.6 to 3.9 billion years ago--"Rockless Eon" - The solidifying of the Earth's continental and oceanic ...28-Apr-2023 ... It accounts for a little less than 4/9ths of geologic time. During the Proterozoic Eon, modern plate tectonics became active, and the ancient ...The Phanerozoic Eon is divided into Eras: Paleozoic, Mesozoic, and Cenozoic. The divisions among Eras reflect major changes in the fossil record, including the extinction and appearance of new life forms. ... the generally accepted divisions are eon, era, period, epoch, age. In the time scale shown at left, only the two highest levels of this ...Feb 5, 2023 · Era: An era is the second largest division of geologic time, following the eon. Eras are still significant spans of time, but they are shorter than eons. Examples of eras include the Mesozoic Era (252 to 66 million years ago), which was the age of dinosaurs, and the Cenozoic Era, which began about 66 million years ago and continues to the present. ….

EON: ERA: PERIOD: EPOCH: PIVOTAL EVENTS: P h a n e r o z o i c E o n "Visible Life" Organisms with skeletons or hard shells. 540 mya through today. P h a n e r o z o i c E o n "Visible Life" Organisms with skeletons or hard shells. 540 mya through today. P h a n e r o z o i c E o n "Visible Life" Organisms with skeletons or hard shells. 540 mya ...Eon-ikum Arkeikum: 4 eoner Eratem Era-ikum Kenozoikum: 10 eror System Period-ogen, -ium, - Neogen, Kambrium, Jura: 22 perioder Serie Epok-ocen, - Eocen, Wenlock: 37 epoker Etage Ålder - Flo, Sandby: 95 åldrar Kronozon Kron - Inga officiellaEon. Era. Period. Quaternary. Cenozoic. Tertiary. Cretaceous. Jurassic. Mesozoic. Triassic. Permian. Carboniferous. Devonian. Silurian. Ordovician. P hanerozoic.This era is marked by 6 periods: Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian periods. The Cambrian period was the time period that saw the largest increase in both the ...eon, Long span of geologic time. In formal usage, eons are the longest portions of geologic time (era s are the second-longest). Three eons are recognized: the Phanerozoic Eon (dating from the present back to the beginning of the Cambrian Period), the Proterozoic Eon, and the Archean Eon. Less formally, eon often refers to a span of one billion ... Eon-ikum Arkeikum: 4 eoner Eratem Era-ikum Kenozoikum: 10 eror System Period-ogen, -ium, - Neogen, Kambrium, Jura: 22 perioder Serie Epok-ocen, - Eocen, Wenlock: 37 epoker Etage Ålder - Flo, Sandby: 95 åldrar Kronozon Kron - Inga officiellaThe Phanerozoic Eon is the current eon in the geologic time scale. It began around 541 million years ago (mya), and encompasses Earth’s history from then to the present day. It represents around 12% of Earth’s total history. Preceding the Phanerozoic Eon was the Proterozoic Eon. The Phanerozoic Eon began with an event known as the Cambrian ...The history of the earth is broken up into a hierarchical set of divisions for describing geologic time. As increasingly smaller units of time, the generally accepted divisions are eon, era, period, epoch, age. In the time scale shown at left, only the two highest levels of this hierarchy are represented. The Phanerozoic Eon is shown along the ...The history of the earth is broken up into a hierarchical set of divisions for describing geologic time. As increasingly smaller units of time, the generally accepted divisions are eon, era, period, epoch, age. In the time scale shown at left, only the two highest levels of this hierarchy are represented. The Phanerozoic Eon is shown along the ...Hadean Eon, informal division of the Precambrian occurring between about 4.6 billion and about 4.0 billion years ago. It was the time … Eon era period, 10 Qs. Types of Energy. 1.6K plays. 1st - 3rd. Earth's History & Geologic Time Review quiz for 6th grade students. Find other quizzes for Other Sciences and more on Quizizz for free!, The Cenozoic Era is the most recent and the Paleozoic Era is the oldest of the three. 3. ... From longest to shortest, the segments of time are eon, era, period, and epoch. 5., Joseon [a] ( Korean : 조선; Hanja : 朝鮮; MR : Chosŏn; [tɕo.sʌn] ), officially Great Joseon ( 대조선국; [tɛ.tɕo.sʌn.ɡuk̚] ), [14] was the last dynastic kingdom of Korea, lasting just over 500 years. [15] [16] It was founded by Yi Seong-gye in July 1392 and replaced by the Korean Empire in October 1897. [17], Phanerozoic Eon. The Phanerozoic Eon is divided into three eras, the Paleozoic, Mesozoic and Cenozoic eras. These were named for the kinds of fossils that were present. The Cenozoic is the youngest era and the name means “new life”. This is because the fossils are similar to animals and plants that are common today., The Precambrian Eon. Hadean era: 4.5 bya - 4 bya. The planet is formed but has yet to cool. Begins pulling gas and dust from space to form our atmosphere. All the water now on Earth was still evaporated in the atmosphere. Asteroid impacts were common., a. the place on the surface directly above the focus. b. a spot halfway between the focus and the surface. c. the spot below the focus. d. any spot along the nearest fault. a. the place on the surface directly above the focus. The most common Precambrian fossils are layered mounds of calcium carbonate called ______., The Cryogenian (from Ancient Greek: κρύος, romanized: krýos, meaning "cold" and γένεσις, romanized: génesis, meaning "birth") is a geologic period that lasted from It forms the second geologic period of the Neoproterozoic Era, preceded by the Tonian Period and followed by the Ediacaran.. The Cryogenian was a time of drastic biosphere changes., Archeozoic Eon (Archean) 3.9 to 2.5 billion years ago--"Ancient Life" - The first life forms evolve - one celled organisms. Blue-green algae, archaeans, and bacteria appear in the sea. This begins to free oxygen into the atmosphere. Hadean Eon 4.6 to 3.9 billion years ago--"Rockless Eon" - The solidifying of the Earth's continental and oceanic ..., The Archean Eon ( IPA: / ɑːrˈkiːən / ar-KEE-ən, also spelled Archaean or Archæan ), in older sources sometimes called the Archaeozoic, is the second of the four geologic eons of Earth 's history, preceded by the Hadean Eon and followed by the Proterozoic. The Archean represents the time period from 4,000 to 2,500 Ma (millions of years ago)., The subdivision of the geologic time scale that represents the longest time span is called a (n) ______. Era. Beginning with the longest, and ending with the shortest, which of the following denotes the divisions of the geologic time scale in correct order? Eon, Era, Period, Epoch. Consider the names of the eras in the geologic time scale. , Geological Time Scale infographic diagram including EON ERA period epoch age and features for geology science education and earth layers history table ..., About the geologic time scale divisions. The geologic history of the Earth is broken up into hierarchical chunks of time. From largest to smallest, this hierarchy includes eons, eras, periods, epochs, and ages. All of these are displayed in the portion of the geologic time scale shown below. Eon. , The geologic time scale (GTS) is a system of chronological dating that relates geological strata (stratigraphy) to time, and is used by geologists, paleontologists, and other Earth scientists to describe the timing and relationships of events that have occurred during Earth's history. Rise of humans, earliest writing in c. 3200 B.C., human ..., epoch, period, era, eon. 36. Multiple-choice. 30 seconds. 1 pt. The amount of time it takes for one-half of the original amount of an isotope to decay is known as its, Eon. Era. Period. Quaternary. Cenozoic. Tertiary. Cretaceous. Jurassic. Mesozoic. Triassic. Permian. Carboniferous. Devonian. Silurian. Ordovician. P hanerozoic., This problem has been solved! You'll get a detailed solution from a subject matter expert that helps you learn core concepts. See Answer. Question: Which of the following answers arranges the time periods listed in the correct order from LONGEST to SHORTEST? Stage, Era, Period Era, Period, Stage Stage, Period, Era Period, Stage, Era Era, Stage ..., Eon is the largest division of time, followed by era, period, epoch, and age. The partitions of the geologic time scale is the same everywhere on Earth; however, rocks may or may not be present at a given location depending on the geologic activity going on …, Era, a very long span of geological time; in formal usage, the second longest portion of geologic time after an eon. Ten eras are recognized by the International Union of Geological Sciences. An era is composed of one or more geological periods. The stratigraphic, or rock, term that corresponds to ‘era’ is ‘erathem.’., 08-May-2001 ... "Eon" also means any span of one billion years. 2nd Order, Erathem, Era, A geologic division including several periods, but smaller than an eon., The Phanerozoic eon—the past 540 Ma of Earth’s history—is divided into three eras: the Paleozoic (“early life”), the Mesozoic (“middle life”), and the Cenozoic (“new life”), and each of these is divided into a number of periods (Figure 8.1.3). Most of the organisms that we share Earth with evolved at, Feb 28, 2020 · Eon: Era: Period: Dates (Ma) Phanerozoic: Cenozoic: Quaternary: 2.58-0: Neogene: 23.03-2.58: Paleogene: 66-23.03: Mesozoic: Cretaceous: 145-66: Jurassic: 201-145: Triassic: 252-201: Paleozoic: Permian: 299-252: Carboniferous: 359-299: Devonian: 419-359: Silurian: 444-419: Ordovician: 485-444: Cambrian: 541-485: Proterozoic: Neoproterozoic ... , The Triassic Period is part of the Mesozoic Era and Phanerozoic Eon. The Triassic period has 3 epochs and 7 ages. Each of these shorter divisions of time identifies a notable event or characteristic feature based on its record. The Triassic period started 252 million years ago after Earth’s largest extinction event in history., The subdivision of the geologic time scale that represents the longest time span is called a (n) ______. Era. Beginning with the longest, and ending with the shortest, which of the following denotes the divisions of the geologic time scale in correct order? Eon, Era, Period, Epoch. Consider the names of the eras in the geologic time scale., Although astronomers and geologists use the word “eon” to mean 1 billion years, it is more commonly used to refer to any long, indefinite period of time. Like the words “age,” “epoch” and “era,” it does not refer to a set number of years., eon - era - period - epoch. Boundaries between intervals of the geological time scale are determined by. major events in the Earth's history, such as major extinctions., Eonothem / Eon Erathem / Era GSSP age (Ma) Eonothem / Eon Erathem / Era System / Period Series / Epoch Stage / Age GSSP Eonothem / Eon Erathem / Era Series / Epoch Stage / Age GSSP GSSA INTERNATIONAL CHRONOSTRATIGRAPHIC CHART International Commission on Stratigraphy Colouring follows the Commission for the …, eon = The largest unit of time. era = A unit of time shorter than an eon but longer than a period. period = A unit of time shorter than an era but longer than epoch. epoch = A unit of time shorter than a period but longer than an age. Archean = “Ancient” eon from 4,500 Mya – 2,500 Ma. Proterozoic = “Early life” eon from 2,500 Ma ... , As of April 2022 there are currently ten defined eras/erathems, namely the Eoarchean, Paleoarchean, Mesoarchean, Neoarchean, Paleoproterozoic, Mesoproterozoic, Neoproterozoic, Paleozoic, Mesozoic and Cenozoic, with none from the Hadean eon. A period is a major rank below an era and … See more, , The Phanerozoic Eon covers 541 million years and includes three major geological eras: the Paleozoic, Mesozoic and, Cenozoic. Three definitions for Eon are: 1. An indefinitely long period of time ..., B. eon, era, period, epoch Assume that man's recorded history can be stretched back to 4600 years before the present. This is approximately what fraction of geologic time?, eon, Long span of geologic time. In formal usage, eons are the longest portions of geologic time (era s are the second-longest). Three eons are recognized: the Phanerozoic Eon (dating from the present back to the beginning of the Cambrian Period), the Proterozoic Eon, and the Archean Eon. Less formally, eon often refers to a span of one billion ... , 10 oct 2016 ... La Tierra, tan vieja que medimos su edad en eones. Todos tenemos claro que un eón es un largo, larguísimo periodo de tiempo ...