विकिपीडिया

भूवैज्ञानिक समय-मान

(भूवैज्ञानिक इओन से अनुप्रेषित)

भूवैज्ञानिक समय-मान (geologic time scale) कालानुक्रमिक मापन की एक प्रणाली है जो स्तरिकी (stratigraphy) को समय के साथ जोड़ती है। यह एक स्तरिक सारणी (stratigraphic table) है। भूवैज्ञानिक, जीवाश्मवैज्ञानिक तथा पृथ्वी का अध्ययन करने वाले अन्य वैज्ञानिक इसका प्रयोग धरती के सम्पूर्ण प्राकृतिक इतिहास में हुई सभी घटनाओं का समय अनुमान करने के लिये करते हैं। जिस प्रकार चट्टानो के अधिक पुराने स्तर नीचे होते हैं तथा नये स्तर उपर होते हैं, उसी प्रकार इस सारणी में पुराने काल और घटनाएँ नीचे हैं जबकि नवीन घटनाएँ उपर (पहले) दी जाती हैं। विकिरणमितीय प्रमाणों (radiometric evidence) से पता चलता है पृथ्वी की आयु लगभग 4.54 अरब वर्ष है।[1][2]

यह घड़ी भूवैज्ञानिक काल के प्रमुख ईकाइयों के के साथ-साथ पृथ्वी के जन्म से लेकर आज तक की प्रमुख घटनाओं को भी दिखा रही है।

परिभाषा

संपादित करें
  • भूवैज्ञानिक समय के सबसे बड़े खंडों को इओन (eon) कहते हैं।[3] यह शब्द यूनानी भाषा से लिया गया है और, क्योंकि संस्कृत और यूनानी दोनों हिन्द-यूरोपीय भाषा परिवार की दो बहन भाषाएँ हैं, इसलिए इस शब्द का संस्कृत में एक सजातीय शब्द मिलता है, "आयु"।[4] पृथ्वी पर चार इओन निर्धारित करे गये हैं: हेडियन (Hadean), आर्कीअन (Archean), प्रोटेरोज़ोइक (Proterozoic) और दृश्यजीवी (फ़ैनेरोज़ोइक, Phanerozoic)। इनमें से पहली तीन इओनों को सामूहिक रूप से कैम्ब्रीयनपूर्व महाइओन (Precambrian supereon) कहा जाता है।
  • इओन को आगे महाकल्प (era) में विभाजित करा जाता है।
  • महाकल्प को कल्प (period) में विभाजित करा जाता है।
  • कल्प को युग (epoch) में विभाजित करा जाता है।
  • युग को काल (age) में विभाजित करा जाता है।

भूवैज्ञानिक काल एवं उनका निर्धारण

संपादित करें

भूवैज्ञानिक कालों का निर्धारण करना सहज कार्य नहीं है। समय-समय पर अनेक विद्वानों ने इस विषय पर कई सिद्धांत प्रतिपादित किए हैं। इन कालों (महाकल्पों, कल्पों तथा युगों) के विभाजन का पारम्परिक आधार यूरोप एवं उत्तर अमरीका के तटवर्ती सागरों की तलहटियों में हुए परिवर्तन हैं। कालों का विभाजन करनेवाली सीमाएँ वास्तविक न होकर मात्र सुविधानुसार हैं।

अकशेरुकीय जंतुओं के जीवन में परिवर्तन अथवा अवसादों के निक्षेपण में व्यवधान को लक्ष्य करके कालों को विभाजित कर लिया गया है। कैम्ब्रियन कल्प से लेकर नूतन महाकल्प तक, अनुमानतः, 50 करोड़ वर्षों का विस्तार रहा है। शिलाखंडों की पहचान कर लेने के बाद सबसे प्राचीन खंड की आयु तीन अरब वर्ष पूर्व की आँकी गई है। कैम्ब्रियन काल में ही पहली बार जीवाश्म दिखलाई पड़ते हैं; उनकी आयु 50 करोड़ पूर्व मानी गई है। इसका यह अर्थ नहीं निकालना चाहिए कि इसके पूर्व पृथ्वी पर जीवन था ही नहीं। जीवन अवश्यमेव था, नहीं तो जीवाश्म कहाँ से प्राप्त होते। यह दूसरी बात है कि जीवन के उस आदिम काल के प्रमाण हमें उपलब्ध नहीं हैं, क्योंकि उनका क्रमिक उद्विकास हो रहा था।

प्रथम कशेरुकीय जंतु की उत्पत्ति अनुमानतः 40 करोड़ वर्ष पूर्व हुई थी, जो ऑर्डोविसियन कल्प के नाम से जाना जाता है। विख्यात दैत्याकार डाइनासौर लगभग 20 करोड़ वर्ष पूर्व उत्पन्न हुए और प्रायः 1 करोड़ वर्षों तक पृथ्वी पर भ्रमण करते रहे। सात करोड़ वर्ष पूर्व स्तनपायी (mammals) जंतु प्रकट हुए और डाइनासौर लुप्त हो गए। मनुष्य के उत्पत्ति लगभग 10 लाख वर्ष पूर्व मानी जाती है।

जीवाश्मों तथा भूगर्भिक कालों में अटूट संबंध होता है। ये भूवैज्ञानिक काल कौन-कौन से हैं, इसका संक्षिप्त परिचय निम्नलिखित है :

इओन महाकल्प कल्प समय, करोड़
वर्ष पूर्व 		विस्तार, करोड़
वर्ष
दृश्यजीवी
Phanerozoic 		नूतनजीवी
Cenozoic 		चतुर्थ (प्लाइस्टोसीन​/होलोसीन)
Quaternary (Pleistocene/Holocene) 		0.2588–0 0.2588+
नियोजीन (मायोसीन/प्लायोसीन)
Neogene (Miocene/Pliocene) 		2.303–0.2588 2.04
पेलियोजीन (पेलियोसीन/इयोसीन/ओलिगोसीन)
Paleogene (Paleocene/Eocene/Oligocene) 		6.60–2.303 4.29
मध्यजीवी
Mesozoic 		चाकमय
Cretaceous 		14.55–6.60 7.95
जुरैसिक
Jurassic 		20.13–14.50 5.63
ट्राइऐसिक
Triassic 		25.217–20.13 5.09
पुराजीवी
Paleozoic 		पर्मियन
Permian 		29.89–25.217 4.67
कार्बनी (मिसिसिपियाई/पेनसिलवेनियाई)
Carboniferous (Mississippian/Pennsylvanian) 		35.89–29.89 6.0
डिवोनी
Devonian 		41.92–35.89 6.03
सिल्यूरियाई
Silurian 		44.34–41.92 2.42
ओर्डोविशी
Ordovician 		48.54–44.34 4.2
कैम्ब्रियाई
Cambrian 		54.10–48.54 5.56
प्राग्जीवी
Proterozoic 		नूतनप्राग्जीवी
Neoproterozoic 		इडिऐकरन
Ediacaran 		63.50–54.10 9.4
क्रायोजेनियाई
Cryogenian 		85.0–63.5 21.5
टोनियाई
Tonian 		100.0–85.0 15.0
मध्यप्राग्जीवी
Mesoproterozoic 		स्टेनियाई
Stenian 		120.0–100.0 20.0
एक्टेशियाई
Ectasian 		140.0–120.0 20.0
कैलिमियाई
Calymmian 		160.0–140.0 20.0
पुराप्राग्जीवी
Paleoproterozoic 		स्टाथेरियाई
Statherian 		180.0–160.0 20.0
ओरोसिरियाई
Orosirian 		205.0–180.0 25.0
राएसियाई
Rhyacian 		230.0–205.0 25.0
साएडेरियाई
Siderian 		250.0–230.0 20.0
आर्कियाई
Archean 		नियोआर्कियाई
Neoarchean 		- 280.0–250.0 30.0
मीसोआर्कियाई
Mesoarchean 		- 320.0–280.0 40.0
पेलियोआर्कियाई
Paleoarchean 		- 360.0–320.0 40.0
इयोआर्कियाई
Eoarchean 		- 400.0–360.0 40.0
आर्कियाई
Hadean 		- - 460.0–400.0 60.0


कालों का नामकरण

संपादित करें

ऊपर की तालिका में प्रत्येक महाकल्प, कल्प तथा युग का कोई न कोई नाम दिया गया है। 'कैम्ब्रियन' नाम इंग्लैंड के वेल्स प्रदेश में स्थित कैम्ब्रिया जिले के नाम पर दिया गया, जहाँ इस काल के शिलाखंड प्रचुर मात्रा में उपलब्ध हुए हैं। 'ऑर्डोविसिन' तथा 'सिल्यूरियन कल्प' का नामकरण दक्षिणी इंग्लैंड तथा वेल्स की इसी नाम की आदिम जातियों के नाम के आधार पर पड़ा है। डिवोनियन कल्प का नामकरण डिवॉनशायर (इंग्लैंड) के नाम पर पड़ा है। इसी प्रकार उत्तरी अमरीका की मिसिसिपी नदी तथा पेंसिल्वैनिया प्रदेश की ऐलेगनी पर्वत श्रेणी के क्षेत्र में पाए गए शिलाखंडों के नाम पड़े हैं। इसी प्रकार उत्तरी भाग में स्थित पर्म प्रदेश में पाए गए पुराजीवी शिलाखंडों को पर्मियन नाम दिया गया। इसी प्रकार अन्य नामों को भी समझना चाहिए।

भूवैज्ञानिक समयरेखा

संपादित करें

Ediacaran PaleoproterozoicMesoproterozoic

HadeanArcheanProterozoicPhanerozoicPrecambrian
CambrianOrdovician

DevonianCarboniferousPermianTriassicJurassicCretaceous

PaleozoicMesozoicCenozoicPhanerozoic
PaleoceneEoceneOligoceneMiocene

PleistocenePaleogeneNeogeneQuaternaryCenozoic
Millions of Years

'एक महाकल्प' को 'एक दिन' के बराबर मानकर तुलना

संपादित करें
वास्तविक
समय [मिलियन वर्ष में]		   1 दिन
का समय
0,01 कृषि तथा पशुपालन 0,2 s
0,13 मानव 2 s
1,5 होमो हैबिलिस 25 s
7 खड़े होकर चलना 2 min
10 मानव-पूर्व 3 min
33 एप्स 10 min
80 वानर 20 min
200 स्तनपोषी 1 h
280 सरीसृप 1 h 20 min
360 उभयचर 1 h 45 min
420 मत्स्य 2 h
470 कशेरुक 2 h 15 min
600 बहुकोशीय जीव 3 h
1000 लैंगिकता 5 h
1500 युकैरियोट 7 h
2200 प्रकाश संश्लेषण 11 h
3200 प्रोटोज़ोआ 15 h
4600 पृथ्वी 23 h

भूवैज्ञानिक काल एवं सम्बन्धित विवरण

संपादित करें

यहाँ दी गयी भूवैज्ञानिक कालों की सारणी अन्तरराष्ट्रीय स्तरिक आयोग द्वारा निर्धारित तिथियों एवं नामकरण के अनुरूप है।

[[Template:|द]] • [[Template talk:|वा]] • [[[:साँचा:Fullurl:साँचा:]] ब]
भूवैज्ञानिक समय-मान (Geologic time scale)
सुपरइओन इओन (Eon) महाकल्प (Era) कल्प (Period)[5] युग (Epoch) काल (Age)[6] प्रमुख घ्टनाएँ आरम्भ (मिलियन वर्ष पूर्व)[6]
n/a Phanerozoic नूतनजीव[7]
Quaternary Holocene

chrons: Subatlantic · Subboreal · Atlantic · Boreal · Preboreal

The last glacial period ends; rise of human civilization. Quaternary Ice Age recedes, and the current interglacial begins. Younger Dryas cold spell occurs, Sahara forms from savannah, and agriculture begins, allowing humans to build cities. Paleolithic/Neolithic (Stone Age) cultures begin around 10000 BC, giving way to Copper Age (3500 BC) and Bronze Age (2500 BC). Cultures continue to grow in complexity and technical advancement through the Iron Age (1200 BC), giving rise to many pre-historic cultures throughout the world, eventually leading into Classical Antiquity, such as the Roman Empire and even to the Middle Ages and present day. Little Ice Age (stadial) causes brief cooling in Northern Hemisphere from 1400 to 1850. Also refer to the List of archaeological periods for clarification on early cultures and ages. Mount Tambora erupts in 1815, causing the Year Without a Summer (1816) in Europe and North America from a volcanic winter. Following the Industrial Revolution, Atmospheric CO2 levels rise from around 280 parts per million volume (ppmv) to the current level of 390 ppmv.[8] 0.011700 ± [7][9]
अत्यंतनूतन Tarantian · Tyrrhenian Stage · Eemian · Sangamonian Flourishing and then extinction of many large mammals (Pleistocene megafauna). Evolution of anatomically modern humans. Quaternary Ice Age continues with glaciations and interstadials (and the accompanying fluctuations from 100 to 300 ppmv in atmospheric CO2 levels[8]), further intensification of Icehouse Earth conditions, roughly 1.6 Ma. Last glacial maximum (30000 years ago), last glacial period (18000–15000 years ago). Dawn of human stone-age cultures, with increasing technical complexity relative to previous ice age cultures, such as engravings and clay statues (e.g. Venus of Lespugue), particularly in the Mediterranean and Europe. Lake Toba supervolcano erupts 75000 years before present, causing a volcanic winter that pushes humanity to the brink of extinction. Pleistocene ends with Oldest Dryas, Older Dryas/Allerød and Younger Dryas climate events, with Younger Dryas forming the boundary with the Holocene. 0.126 ± 0.005*
Ionian 0.781 ± 0.005*
Calabrian 1.806 ± 0.005*
Gelasian 2.588 ± 0.005*
Neogene अतिनूतन Piacenzian/Blancan Intensification of present Icehouse conditions, present (Quaternary) ice age begins roughly 2.58 Ma; cool and dry climate. Australopithecines, many of the existing genera of mammals, and recent mollusks appear. Homo habilis appears. 3.600 ± 0.005*
Zanclean 5.332 ± 0.005*
Miocene Messinian Moderate Icehouse climate, puncuated by ice ages; Orogeny in northern hemisphere. Modern mammal and bird families become recognizable. Horses and mastodons diverse. Grasses become ubiquitous. First apes appear (for reference see the article: "Sahelanthropus tchadensis"). Kaikoura Orogeny forms Southern Alps in New Zealand, continues today. Orogeny of the Alps in Europe slows, but continues to this day. Carpathian orogeny forms Carpathian Mountains in Central and Eastern Europe. Hellenic orogeny in Greece and Aegean Sea slows, but continues to this day. Middle Miocene Disruption occurs. Widespread forests slowly draw in massive amounts of CO2, gradually lowering the level of atmospheric CO2 from 650 ppmv down to around 100 ppmv[8]. 7.246 ± 0.05*
Tortonian 11.608 ± 0.05*
Serravallian 13.65 ± 0.05*
Langhian 15.97 ± 0.05*
Burdigalian 20.43 ± 0.05*
Aquitanian 23.03 ± 0.05*
Paleogene Oligocene Chattian Warm but cooling climate, moving towards Icehouse; Rapid evolution and diversification of fauna, especially mammals. Major evolution and dispersal of modern types of flowering plants 28.4 ± 0.1*
Rupelian 33.9 ± 0.1*
Eocene Priabonian Moderate, cooling climate. Archaic mammals (e.g. Creodonts, Condylarths, Uintatheres, etc) flourish and continue to develop during the epoch. Appearance of several "modern" mammal families. Primitive whales diversify. First grasses. Reglaciation of Antarctica and formation of its ice cap; Azolla event triggers ice age, and the Icehouse Earth climate that would follow it to this day, from the settlement and decay of seafloor algae drawing in massive amounts of atmospheric carbon dioxide[8], lowering it from 3800 ppmv down to 650 ppmv. End of Laramide and Sevier Orogenies of the Rocky Mountains in North America. Orogeny of the Alps in Europe begins. Hellenic Orogeny begins in Greece and Aegean Sea. 37.2 ± 0.1*
Bartonian 40.4 ± 0.2*
Lutetian 48.6 ± 0.2*
Ypresian 55.8 ± 0.2*
Paleocene Thanetian Climate tropical. Modern plants appear; Mammals diversify into a number of primitive lineages following the extinction of the dinosaurs. First large mammals (up to bear or small hippo size). Alpine orogeny in Europe and Asia begins. Indian Subcontinent collides with Asia 55 Ma, Himalayan Orogeny starts between 52 and 48 Ma. 58.7 ± 0.2*
Selandian 61.7 ± 0.3*
Danian 65.5 ± 0.3*
मध्यजीव Cretaceous Late Maastrichtian Flowering plants proliferate, along with new types of insects. More modern teleost fish begin to appear. Ammonoidea, belemnites, rudist bivalves, echinoids and sponges all common. Many new types of dinosaurs (e.g. Tyrannosaurs, Titanosaurs, duck bills, and horned dinosaurs) evolve on land, as do Eusuchia (modern crocodilians); and mosasaurs and modern sharks appear in the sea. Primitive birds gradually replace pterosaurs. Monotremes, marsupials and placental mammals appear. Break up of Gondwana. Beginning of Laramide and Sevier Orogenies of the Rocky Mountains. Atmospheric CO2 close to present-day levels. 70.6 ± 0.6*
Campanian 83.5 ± 0.7*
Santonian 85.8 ± 0.7*
Coniacian 89.3 ± 1.0*
Turonian 93.5 ± 0.8*
Cenomanian 99.6 ± 0.9*
Early Albian 112.0 ± 1.0*
Aptian 125.0 ± 1.0*
Barremian 130.0 ± 1.5*
Hauterivian 136.4 ± 2.0*
Valanginian 140.2 ± 3.0*
Berriasian 145.5 ± 4.0*
Jurassic Late Tithonian Gymnosperms (especially conifers, Bennettitales and cycads) and ferns common. Many types of dinosaurs, such as sauropods, carnosaurs, and stegosaurs. Mammals common but small. First birds and lizards. Ichthyosaurs and plesiosaurs diverse. Bivalves, Ammonites and belemnites abundant. Sea urchins very common, along with crinoids, starfish, sponges, and terebratulid and rhynchonellid brachiopods. Breakup of Pangaea into Gondwana and Laurasia. Nevadan orogeny in North America. Rantigata and Cimmerian Orogenies taper off. Atmospheric CO2 levels 4–5 times the present day levels (1200–1500 ppmv, compared to today's 385 ppmv[8]). 150.8 ± 4.0*
Kimmeridgian 155.7 ± 4.0*
Oxfordian 161.2 ± 4.0*
Middle Callovian 164.7 ± 4.0
Bathonian 167.7 ± 3.5*
Bajocian 171.6 ± 3.0*
Aalenian 175.6 ± 2.0*
Early Toarcian 183.0 ± 1.5*
Pliensbachian 189.6 ± 1.5*
Sinemurian 196.5 ± 1.0*
Hettangian 199.6 ± 0.6*
Triassic Late Rhaetian Archosaurs dominant on land as dinosaurs, in the oceans as Ichthyosaurs and nothosaurs, and in the air as pterosaurs. Cynodonts become smaller and more mammal-like, while first mammals and crocodilia appear. Dicroidium flora common on land. Many large aquatic temnospondyl amphibians. Ceratitic ammonoids extremely common. Modern corals and teleost fish appear, as do many modern insect clades. Andean Orogeny in South America. Cimmerian Orogeny in Asia. Rangitata Orogeny begins in New Zealand. Hunter-Bowen Orogeny in Northern Australia, Queensland and New South Wales ends, (c. 260–225 Ma) 203.6 ± 1.5*
Norian 216.5 ± 2.0*
Carnian 228.0 ± 2.0*
Middle Ladinian 237.0 ± 2.0*
Anisian 245.0 ± 1.5*
Early Olenekian 249.7 ± 1.5*
Induan 251.0 ± 0.7*
Paleozoic Permian Lopingian Changhsingian Landmasses unite into supercontinent Pangaea, creating the Appalachians. End of Permo-Carboniferous glaciation. Synapsid reptiles (pelycosaurs and therapsids) become plentiful, while parareptiles and temnospondyl amphibians remain common. In the mid-Permian, coal-age flora are replaced by cone-bearing gymnosperms (the first true seed plants) and by the first true mosses. Beetles and flies evolve. Marine life flourishes in warm shallow reefs; productid and spiriferid brachiopods, bivalves, forams, and ammonoids all abundant. Permian-Triassic extinction event occurs 251 Ma: 95% of life on Earth becomes extinct, including all trilobites, graptolites, and blastoids. Ouachita and Innuitian orogenies in North America. Uralian orogeny in Europe/Asia tapers off. Altaid orogeny in Asia. Hunter-Bowen Orogeny on Australian Continent begins (c. 260–225 Ma), forming the MacDonnell Ranges. 253.8 ± 0.7*
Wuchiapingian 260.4 ± 0.7*
Guadalupian Capitanian 265.8 ± 0.7*
Wordian/Kazanian 268.4 ± 0.7*
Roadian/Ufimian 270.6 ± 0.7*
Cisuralian Kungurian 275.6 ± 0.7*
Artinskian 284.4 ± 0.7*
Sakmarian 294.6 ± 0.8*
Asselian 299.0 ± 0.8*
Carbon-
iferous[10]/
Pennsyl-
vanian 		Late Gzhelian Winged insects radiate suddenly; some (esp. Protodonata and Palaeodictyoptera) are quite large. Amphibians common and diverse. First reptiles and coal forests (scale trees, ferns, club trees, giant horsetails, Cordaites, etc.). Highest-ever atmospheric oxygen levels. Goniatites, brachiopods, bryozoa, bivalves, and corals plentiful in the seas and oceans. Testate forams proliferate. Uralian orogeny in Europe and Asia. Variscan orogeny occurs towards middle and late Mississippian Periods. 303.9 ± 0.9*
Kasimovian 306.5 ± 1.0*
Middle Moscovian 311.7 ± 1.1*
Early Bashkirian 318.1 ± 1.3*
Carbon-
iferous[10]/
Missis-
sippian 		Late Serpukhovian Large primitive trees, first land vertebrates, and amphibious sea-scorpions live amid coal-forming coastal swamps. Lobe-finned rhizodonts are dominant big fresh-water predators. In the oceans, early sharks are common and quite diverse; echinoderms (especially crinoids and blastoids) abundant. Corals, bryozoa, goniatites and brachiopods (Productida, Spiriferida, etc.) very common, but trilobites and nautiloids decline. Glaciation in East Gondwana. Tuhua Orogeny in New Zealand tapers off. 326.4 ± 1.6*
Middle Viséan 345.3 ± 2.1*
Early Tournaisian 359.2 ± 2.5*
Devonian Late Famennian First clubmosses, horsetails and ferns appear, as do the first seed-bearing plants (progymnosperms), first trees (the progymnosperm Archaeopteris), and first (wingless) insects. Strophomenid and atrypid brachiopods, rugose and tabulate corals, and crinoids are all abundant in the oceans. Goniatite ammonoids are plentiful, while squid-like coleoids arise. Trilobites and armoured agnaths decline, while jawed fishes (placoderms, lobe-finned and ray-finned fish, and early sharks) rule the seas. First amphibians still aquatic. "Old Red Continent" of Euramerica. Beginning of Acadian Orogeny for Anti-Atlas Mountains of North Africa, and Appalachian Mountains of North America, also the Antler, Variscan, and Tuhua Orogeny in New Zealand. 374.5 ± 2.6*
Frasnian 385.3 ± 2.6*
Middle Givetian 391.8 ± 2.7*
Eifelian 397.5 ± 2.7*
Early Emsian 407.0 ± 2.8*
Pragian 411.2 ± 2.8*
Lochkovian 416.0 ± 2.8*
Silurian Pridoli no faunal stages defined First Vascular plants (the rhyniophytes and their relatives), first millipedes and arthropleurids on land. First jawed fishes, as well as many armoured jawless fish, populate the seas. Sea-scorpions reach large size. Tabulate and rugose corals, brachiopods (Pentamerida, Rhynchonellida, etc.), and crinoids all abundant. Trilobites and mollusks diverse; graptolites not as varied. Beginning of Caledonian Orogeny for hills in England, Ireland, Wales, Scotland, and the Scandinavian Mountains. Also continued into Devonian period as the Acadian Orogeny, above. Taconic Orogeny tapers off. Lachlan Orogeny on Australian Continent tapers off. 418.7 ± 2.7*
Ludlow/Cayugan Ludfordian 421.3 ± 2.6*
Gorstian 422.9 ± 2.5*
Wenlock Homerian/Lockportian 426.2 ± 2.4*
Sheinwoodian/Tonawandan 428.2 ± 2.3*
Llandovery/
Alexandrian 		Telychian/Ontarian 436.0 ± 1.9*
Aeronian 439.0 ± 1.8*
Rhuddanian 443.7 ± 1.5*
Ordovician Late Hirnantian Invertebrates diversify into many new types (e.g., long straight-shelled cephalopods). Early corals, articulate brachiopods (Orthida, Strophomenida, etc.), bivalves, nautiloids, trilobites, ostracods, bryozoa, many types of echinoderms (crinoids, cystoids, starfish, etc.), branched graptolites, and other taxa all common. Conodonts (early planktonic vertebrates) appear. First green plants and fungi on land. Ice age at end of period. 445.6 ± 1.5*
other faunal stages 460.9 ± 1.6*
Middle Darriwilian 468.1 ± 1.6*
other faunal stages 471.8 ± 1.6*
Early Arenig 478.6 ± 1.7*
Tremadocian 488.3 ± 1.7*
Cambrian Furongian other faunal stages Major diversification of life in the Cambrian Explosion. Numerous fossils; most modern animal phyla appear. First chordates appear, along with a number of extinct, problematic phyla. Reef-building Archaeocyatha abundant; then vanish. Trilobites, priapulid worms, sponges, inarticulate brachiopods (unhinged lampshells), and many other animals numerous. Anomalocarids are giant predators, while many Ediacaran fauna die out. Prokaryotes, protists (e.g., forams), fungi and algae continue to present day. Gondwana emerges. Petermann Orogeny on the Australian Continent tapers off (550–535 Ma). Ross Orogeny in Antarctica. Adelaide Geosyncline (Delamerian Orogeny), majority of orogenic activity from 514–500 Ma. Lachlan Orogeny on Australian Continent, c. 540–440 Ma. Atmospheric CO2 content roughly 20–35 times present-day (Holocene) levels (6000 ppmv compared to today's 385 ppmv)[8] 496.0 ± 2.0*
Paibian/Ibexian/
Ayusokkanian/Sakian/
Aksayan 		501.0 ± 2.0*
Middle other faunal stages/Albertan 513.0 ± 2.0
Early other faunal stages/
Waucoban/Tommotian/
Atdabanian/Botomian 		542.0 ± 1.0*
Precam-
brian[11] 		Proter-
ozoic[12] 		Neo-
proterozoic[12] 		Ediacaran Good fossils of the first multi-celled animals. Ediacaran biota flourish worldwide in seas. Simple trace fossils of possible worm-like Trichophycus, etc. First sponges and trilobitomorphs. Enigmatic forms include many soft-jellied creatures shaped like bags, disks, or quilts (like Dickinsonia). Taconic Orogeny in North America. Aravalli Range orogeny in Indian Subcontinent. Beginning of Petermann Orogeny on Australian Continent. Beardmore Orogeny in Antarctica, 633–620 Ma. 630 +5/-30*
Cryogenian Possible "Snowball Earth" period. Fossils still rare. Rodinia landmass begins to break up. Late Ruker / Nimrod Orogeny in Antarctica tapers off. 850[13]
Tonian Rodinia supercontinent persists. Trace fossils of simple multi-celled eukaryotes. First radiation of dinoflagellate-like acritarchs. Grenville Orogeny tapers off in North America. Pan-African orogeny in Africa. Lake Ruker / Nimrod Orogeny in Antarctica, 1000 ± 150 Ma. Edmundian Orogeny (c. 920 - 850 Ma), Gascoyne Complex, Western Australia. Adelaide Geosyncline laid down on Australian Continent, beginning of Adelaide Geosyncline (Delamerian Orogeny) in that continent. 1000[13]
Meso-
proterozoic[12] 		Stenian Narrow highly metamorphic belts due to orogeny as Rodinia forms. Late Ruker / Nimrod Orogeny in Antarctica possibly begins. Musgrave Orogeny (c. 1080 Ma), Musgrave Block, Central Australia. 1200[13]
Ectasian Platform covers continue to expand. Green algae colonies in the seas. Grenville Orogeny in North America. 1400[13]
Calymmian Platform covers expand. Barramundi Orogeny, McArthur Basin, Northern Australia, and Isan Orogeny, c. 1600 Ma, Mount Isa Block, Queensland 1600[13]
Paleo-
proterozoic[12] 		Statherian First complex single-celled life: protists with nuclei. Columbia is the primordial supercontinent. Kimban Orogeny in Australian Continent ends. Yapungku Orogeny on Yilgarn craton, in Western Australia. Mangaroon Orogeny, 1680–1620 Ma, on the Gascoyne Complex in Western Australia. Kararan Orogeny (1650-Ma), Gawler Craton, South Australia. 1800[13]
Orosirian The atmosphere becomes oxygenic. Vredefort and Sudbury Basin asteroid impacts. Much orogeny. Penokean and Trans-Hudsonian Orogenies in North America. Early Ruker Orogeny in Antarctica, 2000 - 1700 Ma. Glenburgh Orogeny, Glenburgh Terrane, Australian Continent c. 2005–1920 Ma. Kimban Orogeny, Gawler craton in Australian Continent begins. 2050[13]
Rhyacian Bushveld Igneous Complex forms. Huronian glaciation. 2300[13]
Siderian Oxygen catastrophe: banded iron formations forms. Sleaford Orogeny on Australian Continent, Gawler Craton 2440–2420 Ma. 2500[13]
Archean[12] Neoarchean[12] Stabilization of most modern cratons; possible mantle overturn event. Insell Orogeny, 2650 ± 150 Ma. Abitibi greenstone belt in present-day Ontario and Quebec begins to form, stablizes by 2600 Ma. 2800[13]
Mesoarchean[12] First stromatolites (probably colonial cyanobacteria). Oldest macrofossils. Humboldt Orogeny in Antarctica. Blake River Megacaldera Complex begins to form in present-day Ontario and Quebec, ends by roughly 2696 Ma. 3200[13]
Paleoarchean[12] First known oxygen-producing bacteria. Oldest definitive microfossils. Oldest cratons on Earth (such as the Canadian Shield and the Pilbara Craton) may have formed during this period[14]. Rayner Orogeny in Antarctica. 3600[13]
Eoarchean[12] Simple single-celled life (probably bacteria and archaea). Oldest probable microfossils. 3800
Hadean
[12][15] 		Early Imbrian[12][16] Indirect photosynthetic evidence (e.g., kerogen) of primordial life. This era overlaps the end of the Late Heavy Bombardment of the inner solar system. c.3850
Nectarian[12][16] This unit gets its name from the lunar geologic timescale when the Nectaris Basin and other greater lunar basins form by big impact events. c.3920
Basin Groups[12][16] Oldest known rock (4030 Ma)[17]. The first life forms and self-replicating RNA molecules evolve around 4000 Ma, after the Late Heavy Bombardment ends on Earth. Napier Orogeny in Antarctica, 4000 ± 200 Ma. c.4150
Cryptic[12][16] Oldest known mineral (Zircon, 4404 ± 8 Ma).[18] Formation of Moon (4533 Ma), probably from giant impact. Formation of Earth (4567.17 to 4570 Ma) c.4570


सन्दर्भ

संपादित करें
  1. ↑ "Age of the Earth". U.S. Geological Survey. 1997. मूल से 23 दिसंबर 2005 को पुरालेखित. अभिगमन तिथि 2006-01-10.
  2. ↑ Dalrymple, G. Brent (2001). "The age of the Earth in the twentieth century: a problem (mostly) solved". Special Publications, Geological Society of London. 190 (1): 205–221. डीओआइ:10.1144/GSL.SP.2001.190.01.14. बिबकोड:2001GSLSP.190..205D.
  3. ↑ "मेघालय का दौर". मूल से 20 जुलाई 2018 को पुरालेखित. अभिगमन तिथि 20 जुलाई 2018.
  4. ↑ "English and Sanskrit, a common heritage of words: with special reference to Punjabi," G. S. Rayall, Publication Bureau, Punjabi University, 1996, ... IE. aiw-, age ; whence also Lat. avum, age, ( see Eng. medieval ) ; Gk. aeon, a long or indefinite period of time ( see Eng. aeon ). ayu, 3n^, duration of life. Cf. Hind, ayu ...
  5. ↑ Paleontologists often refer to faunal stages rather than geologic (geological) periods. The stage nomenclature is quite complex. For an excellent time-ordered list of faunal stages, see "The Paleobiology Database". अभिगमन तिथि 2006-03-19.
  6. ↑ अ आ Dates are slightly uncertain with differences of a few percent between various sources being common. This is largely due to uncertainties in radiometric dating and the problem that deposits suitable for radiometric dating seldom occur exactly at the places in the geologic column where they would be most useful. The dates and errors quoted above are according to the International Commission on Stratigraphy 2004 time scale. Dates labeled with a * indicate boundaries where a Global Boundary Stratotype Section and Point has been internationally agreed upon: see List of Global Boundary Stratotype Sections and Points for a complete list.
  7. ↑ अ आ Historically, the Cenozoic has been divided up into the Quaternary and Tertiary sub-eras, as well as the Neogene and Paleogene periods. The 2009 version of the ICS time chart recognizes a slightly extended Quaternary as well as the Paleogene and a truncated Neogene, the Tertiary having been demoted to informal status.
  8. ↑ अ आ इ ई उ ऊ For more information on this, see the following articles: Earth's atmosphere, carbon dioxide, Carbon dioxide in the Earth's atmosphere, global warming, climate change, Image:Phanerozoic_Carbon_Dioxide.png, Image:65 Myr Climate Change.png, Image:Five Myr Climate Change.png, and Template:DF temperature
  9. ↑ The start time for the Holocene epoch is here given as 11,700 years ago. For further discussion of the dating of this epoch, see Holocene.
  10. ↑ अ आ In North America, the Carboniferous is subdivided into Mississippian and Pennsylvanian Periods.
  11. ↑ The Precambrian is also known as Cryptozoic.
  12. ↑ अ आ इ ई उ ऊ ए ऐ ओ औ क ख ग घ The Proterozoic, Archean and Hadean are often collectively referred to as the Precambrian Time or sometimes, also the Cryptozoic.
  13. ↑ अ आ इ ई उ ऊ ए ऐ ओ औ क ख Defined by absolute age (Global Standard Stratigraphic Age).
  14. ↑ The age of the oldest measurable craton, or continental crust, is dated to 3600–3800 Ma
  15. ↑ Though commonly used, the Hadean is not a formal eon and no lower bound for the Archean and Eoarchean have been agreed upon. The Hadean has also sometimes been called the Priscoan or the Azoic. Sometimes, the Hadean can be found to be subdivided according to the lunar geologic time scale. These eras include the Cryptic and Basin Groups (which are subdivisions of the Pre-Nectarian era), Nectarian, and Early Imbrian units.
  16. ↑ अ आ इ ई These unit names were taken from the Lunar geologic timescale and refer to geologic events that did not occur on Earth. Their use for Earth geology is unofficial.
  17. ↑ Bowring, Samuel A.; Williams, Ian S. (1999). "Priscoan (4.00–4.03 Ga) orthogneisses from northwestern Canada". Contributions to Mineralogy and Petrology. 134 (1): 3. डीओआइ:10.1007/s004100050465. बिबकोड:1999CoMP..134....3B. The oldest rock on Earth is the Acasta Gneiss, and it dates to 4.03 Ga, located in the Northwest Territories of Canada.
  18. ↑ Geology.wisc.edu

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