भूवैज्ञानिक समय-मान

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।

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

• भूवैज्ञानिक समय के सबसे बड़े खंडों को इओन (eon) कहते हैं। 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"। 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

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

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

Millions of Years

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

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

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

भूवैज्ञानिक समय-मान (Geologic time scale)

सुपरइओन	इओन (Eon)	महाकल्प (Era)	कल्प (Period)	युग (Epoch)	काल (Age)	प्रमुख घ्टनाएँ	आरम्भ (मिलियन वर्ष पूर्व)
n/a	Phanerozoic	नूतनजीव
			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.	0.011700 ±
				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), 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.	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, 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).	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/ 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/ 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)	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	Proter- ozoic	Neo- proterozoic	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
			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
		Meso- proterozoic	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
			Ectasian	Platform covers continue to expand. Green algae colonies in the seas. Grenville Orogeny in North America.			1400
			Calymmian	Platform covers expand. Barramundi Orogeny, McArthur Basin, Northern Australia, and Isan Orogeny, c. 1600 Ma, Mount Isa Block, Queensland			1600
		Paleo- proterozoic	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
			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
			Rhyacian	Bushveld Igneous Complex forms. Huronian glaciation.			2300
			Siderian	Oxygen catastrophe: banded iron formations forms. Sleaford Orogeny on Australian Continent, Gawler Craton 2440–2420 Ma.			2500
	Archean	Neoarchean	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
		Mesoarchean	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
		Paleoarchean	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. Rayner Orogeny in Antarctica.				3600
		Eoarchean	Simple single-celled life (probably bacteria and archaea). Oldest probable microfossils.				3800
	Hadean	Early Imbrian	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	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	Oldest known rock (4030 Ma). 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	Oldest known mineral (Zircon, 4404 ± 8 Ma). Formation of Moon (4533 Ma), probably from giant impact. Formation of Earth (4567.17 to 4570 Ma)				c.4570

बाहरी कड़ियाँ

• NASA: Geologic Time
• GSA: Geologic Time Scale
• British Geological Survey: Geological Timechart
• GeoWhen Database
• International Commission on Stratigraphy Time Scale
• पृथ्वी का इतिहास
• National Museum of Natural History - Geologic Time
• SeeGrid: Geological Time Systems Information model for the geologic time scale
• Exploring Time from Planck Time to the lifespan of the universe
• [1] Gradstein, Felix M. et al. (2004) A new Geologic Time Scale, with special reference to Precambrian and Neogene, Episodes, Vol. 27, no. 2 जून 2004 (pdf)
• Lane, Alfred C, and Marble, John Putman 1937. Report of the Committee on the measurement of geologic time