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 …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 ...Geologic time scale with proportional representation of eons/eonothems and eras/erathems. Cenozoic is abbreviated to Cz. The image also shows some notable events in Earth's history and the general evolution of life. A megannus (Ma) represents one million (10 6) years. Alternate representation of the geologic time scale represented as a clock.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 ...As such, the Phanerozoic Eon includes the Paleozoic Era , the Mesozoic Era , and ... Era; Quaternary Period; Silurian Period; Tertiary Period; Triassic Period.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 ...Which EON has no life? The Hadean Era Because of the repeated melting of the rocks on the Earth’s surface, no Earth rocks from this time have survived. The Hadean Era lasted about 700 million years, from around 4.5 billion years ago (bya) to around 3.8 bya. As you might imagine, no life could have survived the Hadean Era.Apr 16, 2022 · This era lasted from the formation of the earth about 4.5 billion years ago to the start of the Paleozoic era… Which of the following shows the correct order of geologic time scale from the longest to the shortest time interval? From longest to shortest, the segments of time are eon, era, period, and epoch. 5. 6. 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 …Oct 5, 2021 · Geologic Time Scale. Humans subdivide time into useable units such as our calendar year, months, weeks, and days; geologists also subdivide time. They have created a tool for measuring geologic time, breaking it into useable, understandable segments. For the purposes of geology, the “calendar” is the geologic time scale. 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 ...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 ...Record the Eon, Era, Period, and Epoch we currently live in. (4 pts) Eon: Era: Period: Epoch: Phanerozoic Cenozoic Quaternary Holocene Geologists view Earth as a system, and the Earth system as the interplay between open systems or “spheres” in the environment.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.An era is smaller than an eon and longer than a period. Geologic Time Scale - A categorization of geological events based on successively smaller time spans: eons, eras, periods, epochs, and ages. Hadean - The earliest eon in the history of the Earth from the first accretion of planetary material until the date of the oldest known rocks.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 ...The Paleozoic Era is literally the era of “old life.”. It lasted from 544 to 245 million years ago and is divided into six periods. Major events in each period of the Paleozoic Era are described in Figure below. The era began with a spectacular burst of new life. This is called the Cambrian explosion.Explanation: Answer link. We live in the Holocene Epoch, of the Quaternary Period, in the Cenozoic Era (of the Phanerozoic Eon).12-Dec-2022 ... Archean eon, Cenozoic era, Eocene Period, Pilocene epoch, Recent age. Phanerozoic eon, Cenozoic era, Quaternary Period, Holocene epoch, Recent ...Feb 22, 2022 · 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 ... 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 timeEon is an 'immeasurably long period of time' (geologically, it is 1,000 million, or a billion years). · epoch (same origin in Ancient Greek, ...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):Eons, eras, periods and epochs. Karl has been Purch's infographics specialist across all editorial properties since 2010.The final time period on the Geologic Time Scale is the Cenozoic Period. With large dinosaurs now extinct, smaller mammals that had survived were able to grow and become dominant. The climate changed drastically over a relatively short period of time, becoming much cooler and drier than during the Mesozoic Era.Eon Era Period Epoch Late Middle Early Late Middle Early You need to fill the following formal units of the geologic time scale: • Eons - Hadean, Archean, ...The original proposal in 2010 divided the Chaotian into two eras and four periods. No numerical upper age limits were provided, only the younger age limit of ~4.5 Ga for the …how to write master of education
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.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.05-Jan-2016 ... We are currently in the Phanerozoic Eon, the Cenozoic Era, the Quaternary Period, and Holocene epoch. http://www.sherpaguides.com/georgia/coast/ ...Oct 20, 2023 · Cenozoic Era, third of the major eras of Earth’s history, beginning about 66 million years ago and extending to the present. It was the interval of time during which the continents assumed their modern configuration and geographic positions and during which Earth’s flora and fauna evolved toward those of the present. Precambrian Time. Learn more about the period that occurred 4.5 billion to 542 million years ago. Precambrian time covers the vast bulk of the Earth's history, starting with the planet's creation ...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.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 ...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.’.Answer: Eon has the longest duration. Eon is further subdivided into eras and era is further subdivided into periods, epochs and stages. An eon can be referred to as indefinite duration or extremely long period of time. Eons is said to have the longest duration because it is more than one era or a period or an epoch. Summary:Prehistoric Life 23-2.6 Million Years Ago. During the course of the Neogene period, life on earth adapted to new ecological niches opened up by global cooling--and some mammals, birds, and reptiles evolved to truly impressive sizes in the process. The Neogene is the second period of the Cenozoic Era (65 million years ago to the present ...special edu
The final time period on the Geologic Time Scale is the Cenozoic Period. With large dinosaurs now extinct, smaller mammals that had survived were able to grow and become dominant. The climate changed drastically over a relatively short period of time, becoming much cooler and drier than during the Mesozoic Era.Question: Neogene UTILI Cenozoic Paleogene Late Phanerozoic Mesozoic LILIT Use the colonic time scale below to answer Question 3.4 and 5. EON ERA PERIOD EPOCH Ma Holocene Quaternary Late Pleistocene -0.011 0.8 Early 2.4 Tate Pliocene 3.6 Early 5.3 Gate 11.2 Miocene Middle 16.4 Early 23.0 Late Tertiary Oligocene 28.5 Early 34.0 Late 41.3 Eocene Middle 49.0 Early 55.805-Jan-2016 ... We are currently in the Phanerozoic Eon, the Cenozoic Era, the Quaternary Period, and Holocene epoch. http://www.sherpaguides.com/georgia/coast/ ...03-May-2023 ... Then we have an era, which is smaller than an eon, but larger than a period. An era represents a time scale of around 60 to several. hundred ...Archean Eon, or Archaean Eon or Archeozoic Eon, Older of the two divisions of Precambrian time. The Archean begins with the formation of the Earth’s crust 4 billion …The Proterozoic Eon, meaning “earlier life,” is the eon of time after the Archean eon and ranges from 2.5 billion years old to 541 million years old.During this time, most of the central parts of the continents had formed and the plate tectonic process had started. Photosynthesis (in organisms like stromatolites) had already been adding oxygen slowly …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. Eon is further subdivided into eras and era is further subdivided into periods, epochs and stages. An eon can be referred to as indefinite duration or extremely ...Feb 22, 2022 · 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 ... 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 ...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.ku volleyball schedule
Time Words: Era, Epoch, and Eon. An epoch, (not to be confused with epic ), like an era, is a period of time. An epoch is longer than an era and can cover more than one lifetime. It is marked by some significant development or series of developments: the feudal epoch, the epoch of exploration. An eon is a very long time indeed.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. Eon, Long span of geologic time. In formal usage, eons are the longest portions of geologic time (eras 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. Lived exclusively during the Mesozoic Era. Animals that have hair and produce milk for their young; evolved during the Mesozoic Era but became dominant during the Cenozoic Era. Study with Quizlet and memorize flashcards containing terms like Geological Time Scale (GTS), eon, era, period, epoch, age, Precambrian Supereon and more. The Devonian (/ d ɪ ˈ v oʊ n i. ən, d ɛ-/ də-VOH-nee-ən, deh-) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, 419.2 million years ago (), to the beginning of the Carboniferous, 358.9 Ma. It is named after Devon, England, where rocks from this period were first studied.. The first significant …Era är den näst största tidsenheten inom den geologiska tidsskalan. En era är del av en eon och kan i sin tur delas in i flera perioder . Era är också en tidrymd i en kalender som startar vid en viss tidpunkt, epoken . what are the eras? 541 mya-present. 1) Paleozoic. 2) Mesozoic. 3) Cenozoic. Paleozoic Era. -origin and initial diversification of animals, land plants, and fungi. -land animals first appear. -ends with the obliteration of almost all multicellular life forms at the end of the Permian period. 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.’. 05-Jan-2016 ... We are currently in the Phanerozoic Eon, the Cenozoic Era, the Quaternary Period, and Holocene epoch. http://www.sherpaguides.com/georgia/coast/ ...Study with Quizlet and memorize flashcards containing terms like time scale, eons, 4 and more.Labeled earth history scheme with epoch, era, period, EON and mass extinctions diagram. Educational inforgraphic with examples, explanation and description. Designers Also Selected These Stock Illustrations. Sadhu (holy man) from India. Geochronological scale.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 ...Labeled earth history scheme with epoch, era, period, EON and mass extinctions diagram. Educational inforgraphic with examples, explanation and description. Designers Also Selected These Stock Illustrations. Sadhu (holy man) from India. Geochronological scale.An era is not a defined number of years. Rather, it is a period of time marked by certain characteristics, such as historical events. In geology, an era is composed of periods. According to the Encyclopedia Britannica, geological eras encom...why i want to teach
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):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.eon; era; period; epoch; age; chron . Subdivisions are termed ‘early’, ‘mid’ or ‘late’. Chronostratigraphy is similar, but is concerned with the relationships between time and the rocks deposited within those time intervals. Chronostratigraphical terms are applied to rocks deposited during specific intervals of time. Mesozoic – The Mesozoic Era, also called the Age of Reptiles and the Age of Conifers, is the second-to-last era of Earth’s geological history, lasting from about 252 to 66 million years ago and comprising the Triassic, Jurassic and Cretaceous Periods. Occurred: 251.902 (+/- 0.24) million years ago – 65 million years ago.The Cambrian explosion was a sharp and sudden increase in the rate of evolution. About 538.8 million years ago, at the onset of the Cambrian Period, intense diversification resulted in more than 35 new animal phyla; however, new discoveries show that the “explosion” started roughly 575 million years ago, near the end of the Proterozoic Eon (2.5 billion to 538.8 million years ago), with the ...Geologic time scale. Diagram of geological time scale as a spiral. Geologic time scale uses the principles and techniques of geology to work out the geological history of the Earth. [1] It looks at the processes which change the Earth's surface and rocks under the surface. Geologists use stratigraphy and paleontology to find out the sequence of ...1 day ago · Study with Quizlet and memorize flashcards containing terms like time scale, eons, 4 and more. The geologic era in which humans have evolved and spread over the Earth is the Cenozoic Era. This time period began roughly 65 million years before the start of the 21st century. The Cenozoic Era began at the end of the Mesozoic Era when th...The geological time scale is divided into four different lengths of time according to the origin of the living organisms; eon, era, period and epoch. Eon: It is the longest duration of time with billions of years in the geological history which is divided into eras. The entire geological history is divided into four eons namely; Hadean eon (4.5 ...Anthropology. Anthropology questions and answers. 1. Explain how fossils are formed and why they are not equally prevalent in all areas (3pts) 2. Define the terms eon era, period, and epoch and specify modern humans' place in geologic time. (3pts) 3. Compare 1 relative dating method with 1 absolute dating method.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.’.In geologic time , the Paleozoic Era, the first era in the Phanerozoic Eon , covers the time between roughly 544 million years ago (mya) and until 245 mya. The Paleozoic Era spans six geologic time periods including the Cambrian Period (544 to 500 mya); Ordovician Period (500 mya to 440 mya); Silurian (440 mya to 410 mya); …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 Paleozoic Era is literally the era of “old life.”. It lasted from 544 to 245 million years ago and is divided into six periods. Major events in each period of the Paleozoic Era are described in Figure below. The era began with a spectacular burst of new life. This is called the Cambrian explosion.05-Jan-2016 ... We are currently in the Phanerozoic Eon, the Cenozoic Era, the Quaternary Period, and Holocene epoch. http://www.sherpaguides.com/georgia/coast/ ...jeffrey dahmer polaroids twitter fotosRailroads 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 first eon of Precambrian time. The eon preceding the Proterozoic. It extends between 4.5 and 2.5 billion years ago. The second eon of Precambrian time, following the Hadean and preceding the Proterozoic. It extends between 3.8 billion and 2.5 billion years before the present. (Ancient). The earliest living cells formed on Earth. In geologic time , the Paleozoic Era, the first era in the Phanerozoic Eon , covers the time between roughly 544 million years ago (mya) and until 245 mya. The Paleozoic Era spans six geologic time periods including the Cambrian Period (544 to 500 mya); Ordovician Period (500 mya to 440 mya); Silurian (440 mya to 410 mya); …--Eogalactic Period - 13550-13200 MYA. --Neogalactic Period - 13200-4680 MYA. -Neoproteimeran Era - 4680-4568 MYA. --Nephelean Period - 4680-4630 MYA. -- ...Phanerozoic Eon, the span of geologic time extending about 541 million years from the end of the Proterozoic Eon (which began about 2.5 billion years ago) to the present. The Phanerozoic, the eon of visible life, is divided into three major spans of time largely on the basis of characteristic assemblages of life-forms: the Paleozoic (541 million to 252 million years ago), Mesozoic (252 million ...Homo sapiens evolve. Study with Quizlet and memorize flashcards containing terms like List the following units of geologic time in order from shortest to longest: eon, epoch, era, period, What are the 2 eons on the geologic time scale? Circle which one is longest., How old is the Earth? and more.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 time The Geologic Time Scale is divided into four eons, ten eras, 22 periods, and several epochs and ages. Each eon, era, period, and epoch is defined by major geological or paleontological events. The eons are the Hadean, Archean, Proterozoic, and Phanerozoic. The Phanerozoic Eon is the eon of visible life, and is divided into three eras: the ... The geological time scale is divided into four different lengths of time according to the origin of the living organisms; eon, era, period and epoch. Eon: It is the longest duration of time with billions of years in the geological history which is divided into eras. The entire geological history is divided into four eons namely; Hadean eon (4.5 ...c. 4,533 Ma - The Precambrian (to c. 539 Ma), now termed a "supereon" but formerly an era, is split into three geological time intervals called eons: Hadean, Archaean and Proterozoic.The latter two are sub-divided into several eras as currently defined. In total, the Precambrian comprises some 85% of geological time from the formation of Earth to the time when creatures first developed ...The correct answer is SuperEon > Eon > Era > Period > Epoch. Key Points. The geologic time scale (GTS) is a system of chronological dating that classifies geological strata in time. It is used by geologists, paleontologists, and other Earth scientists to describe the timing and relationships of events in geologic history.Eon is further subdivided into eras and era is further subdivided into periods, epochs and stages. An eon can be referred to as indefinite duration or extremely ...03-May-2023 ... Then we have an era, which is smaller than an eon, but larger than a period. An era represents a time scale of around 60 to several. hundred ...An epoch, (not to be confused with epic ), like an era, is a period of time. An epoch is longer than an era and can cover more than one lifetime. It is marked by some significant development or series of developments: the feudal epoch, the epoch of exploration. An eon is a very long time indeed. It is the longest period of geological time. snapchat stickers freaky
8.6: Paleozoic. Figure 8.6.1 8.6. 1: The trilobites had a hard exoskeleton and were an early arthropod, the same group that includes modern insects, crustaceans, and arachnids. The Phanerozoic eon is the most recent eon and represents time in which fossils are common, 541 million years ago to today.Time Words: Era, Epoch, and Eon. An epoch, (not to be confused with epic ), like an era, is a period of time. An epoch is longer than an era and can cover more than one lifetime. It is marked by some significant development or series of developments: the feudal epoch, the epoch of exploration. An eon is a very long time indeed.Feb 15, 2017 · In general, an eon is a very long time, comparable to the age of the universe. An epoch is a fixed point in time (like the zero date of a calendar, or the moment a world-changing event occurred), especially one that marks the beginning of a new era. One can “make an epoch” by doing something that changes things forever. 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 …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 ...What eon do we live in? Phanerozoic Eon ; What era do we live in? Cenozoic Era ; What period do we live in? Quaternary Period ; What epoch do we live in? Holocene ...The Cambrian explosion was a sharp and sudden increase in the rate of evolution. About 538.8 million years ago, at the onset of the Cambrian Period, intense diversification resulted in more than 35 new animal phyla; however, new discoveries show that the “explosion” started roughly 575 million years ago, near the end of the Proterozoic Eon (2.5 billion to 538.8 million years ago), with the ...the first eon of Precambrian time. The eon preceding the Proterozoic. It extends between 4.5 and 2.5 billion years ago. The second eon of Precambrian time, following the Hadean and preceding the Proterozoic. It extends between 3.8 billion and 2.5 billion years before the present. (Ancient). The earliest living cells formed on Earth. The U.S. House Oversight Committee is probing a collection of period tracking apps and data brokers in light of emerging concerns about how private health data might be weaponized in the dawning post-Roe v. Wade era. The committee issued le...What eon do we live in? Phanerozoic Eon ; What era do we live in? Cenozoic Era ; What period do we live in? Quaternary Period ; What epoch do we live in? Holocene ...4 car rollback for sale craigslist
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 is an 'immeasurably long period of time' (geologically, it is 1,000 million, or a billion years). · epoch (same origin in Ancient Greek, ...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 moreEra. Based on major world wide changes in types of fossils. Period. Characterized by the types of life that existed worldwide. Epoch. Characterized by differences in life forms that mat vary regionally. Study with Quizlet and memorize flashcards containing terms like Eon, Era, Period and more. 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 ______.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.’.