Earth's Geologic Eras Table

click to a diagram of the geologic eras at Earth (note! text updates are to be found back in that diagram after a certain time only)

->Great Logics Shaped the Earth!

click to a view of how the Earth's landscapes formed

. mountains: the latest tectonics of mountain ranges during the Primary, which is called the 'Hercynian', occurred during the Carboniferous and created, for example, the Appalachians, the mountains ranges in Central Asia, or in Europe. Those mountain ranges were further eroded to null and then, they were often rejuvenated, at the Tertiary, through tectonics again. Today, those are old, or 'Hercynian' massifs, like the Ardennes in France and Belgium. Tectonics, then, during the Secondary, did yield new mountains ranges, at the time when the current form of the continents formed, with the Andes or the Rocky Mountains. The tectonics, after that, with the current continent forms colliding, yielded other ranges, like the Alps or the Himalayas. Those, by resonance, could form and exhaust nearer, but older, reliefs, which occurred, for example, in France, between the Alps and the Jura. The Tertiary and the Secondary did modelate too the relief through rivers (which created valleys, and alluvial rocks) or the glaciers. The relative drying, for varied causes, brought to 'inner seas', like the North, Black or Caspian Seas
. large sedimentary bassins: they were constituted during the Secondary and the Tertiary, like the region of London, for example. Vast seas allowed the formation of thick layers of clay and chalks (during the Jurassic, and with the marine life's sediments of the Cretaceous)
. fundamental minerals: during the Primary, the decomposition of immense forests brought to the formation of coal, or shallow seas allowed immense deposits of salt
. volcanism: the large period of volcanism, on Earth, occurred during the Devonian (Primary, about -400 million years), the Paleocene (Tertiary, about -60 million years), and the Miocene (about -15 million years). Enormous volcanic activites, on a other hand, happened at least 10 times in the past 3 billion years at the Earth, and linked with some of the most profound changes in Earth’s history, the biggest mass extinction included 252 million years ago. Technically, such eruptions are known as 'large igneous provinces' (LIPs) as they have been calculated to occur every 20 million years or so. They happened everywhere worldwide as the most recent one was at 17 million years ago
. miscellaneous formations: first relief formations of the Primary gave the most ancient terrains on the Earth, with the best example in the layers unearthed by the Great Canyon, in the U.S.A.
To that formation of the landscapes of the Earth, the logics of the rocks is superposing or intertwining. All the Earth's rocks -that they conserved their form, or that they were further modified or reworked- are magmatic in origin and are dating back to the formation of the Earth's crust, through volcanism included (granite, basalt, tuff, porphyry, etc.) Those early rocks then were transformed by the erosion into sediments (sands, sandstone, clays and shales, chalks). Both previous types of rocks, the volcanic and the sedimentary ones may yield, when submitted to high pressure, other types, which are often rich in minerals (schists, gneiss, marble, for example)

->The evolution of life at Earth was linked to the great geologicals moves, like plate tectonics, the dinosaurs' asteroid, or the formation of the African Rift) as such moves obliged life to adaptation. In terms of darwinism, the evolution of life mostly proceded with small steps, as far as the sequence of the genome is concerned, as genetical modification which change the order of genes in the genome are most infrequent, in the order of 10 each million years in the case of vertebrates. Scientists thus think that a similar evolutionary pressure exerted upon related species left unchanged the location of a gene on the sequence. Adaptation of species, generally, works based upon a evolutionist pressure like, for example, to escape predators or to fill available ecological niches. A major factor of the evolution is concerning a species reproduction with evolution of some traits aiming to secure that. The vision of the evolution since the origins of life evolved from that of the tree of life, to that of a bushing view, where monophyletic -related to one common ancestor- 'clades' or categories are gathering most of living species into three main branches, the archeans (or bacteries), eubacteries (or life thrieving in thermal source), and eucaryotes (or multicellular beings)

->note: as far as the mass extinctions which the Earth endured, generally, are concerned, a bias might exist in some sense as the number of marine species was more numerous than the land ones and that the data about them are better known as such species were most, and better preserved in sediments. Large impactors at Earth usually resulted from a collision of two asteroids in the Asteroid Belt

Eras	Geologic Features and Plate Tectonics		Climate (Cold means about 10°. C, warms about between 17 and 25° C)	Marine Life	Land Life	Mass Extinctions
PRECAMBRIAN
Hadean (Azoic) 4.5-3.9 billion years ago		Epoch of Earth's formation. No original rock from these eras may be found as the surface of the Earth is smelting rocks only. That time is too the one when Earth is hit by a large asteroid which gives birth to our Moon. Between 4.568 and 4.4 billion years ago, the Earth formed its nucleus and mantle, and it existed for a time a gigantic global magmatic ocean. There are almost no geological traces of the first 500 million years of the Earth. Banded gneiss of the Acasta site in Canada are one of the oldest known continental crust pieces on earth to date. However, some even seem to be aged 4 billion years and older besides that they can bear zircons, minerals of older age. Such gneisses would have been formed at shallow depth under the effect of the heat produced by the impact of a celestial body of at least 6 miles in diameter. It looks like the rotation of our Earth about itself was of 2 to 3 hours only!	Climate is cold. Due to Moon closer to the Earth, Earth is rotating more rapidly than today, maybe about some 12 hour and tides impressively larger	none	none	Few impactors of a size 62 miles (100 km) who destroyed entirely the Earth's crust and ejected the atmosphere into space likely hit early at Earth, when life hadn't started yet. Mass extinctions might occur roughly every 26 to 30 million years, a interval at which our solar system crosses the plane of the Milky Way Galaxy
Archean 3.9-2.5 billion years ago		It is possible that the Archean Earth behaved more like Pluto, with intrusive magnetism than like Jupiterian Io, for example. Earth's crust has formed. Outgassing produces oceans and the atmosphere as water too is added with asteroids and comets. A heavy atmospheric layer forms which triggers torrential rains during millions years. Earth is filled with a vast ocean, which is green in color due to the iron it contains. The surface of Earth was likely blanketed by a global ocean some 3.2 billion years ago, with no land available at all. Sky is red. The first real crust is now forming, from granite instead of basalt. Earth’s atmosphere seems to have been quite different then, probably with little available oxygen but high levels of methane, ammonia and other organic chemicals. The Late Archean era could have had the Earth's atmosphere richer in CO2 than in oxygen, as that statement would help resolve how the period kept its usual temperature as the young Sun was 20 percent fainter. Geological evidence suggests that haze might have come and gone sporadically from the Archean atmosphere and researchers aren't quite sure why. Plate tectonics on the other hand, was likely already at work on Earth 3.2 billion years ago	Climate is cold	Life appears in the oceans (prokaryotes or archaea: unicellular organisms with no nucleus, likely rock-chewing bacteria). Most archaea have small basic proteins that are likely to share a common evolutionary ancestor with some processes in the eukaryots -- the next form of life -- in terms of DNA. >With some primitive versions of certain eukaryotic properties, last archaea preceding eukaryotes might have displayed a certain -- albeit probably limited -- degree of cellular complexity reminiscent of the latter. Algae are the only form of life. The most ancient trace of life, at 3.5 billion years, consists into bacterial filaments	none	Once the 'Heavy Bombardment Period' over, objects 6.2-62 miles (10-100 km), hitting every 20 million years would have hindered the development of life, leaving not enough time between blows to recover and reducing the life's diversity. The Earth might have been shielded from such effect by the migrations of Jupiter or Saturn, which eventually pushed Uranus, Neptune and the Kuiper Belt farther from the Sun
Proterozoic 2.5 billion-540 million years ago		By 1.5 billion years ago, Earth now takes 15 hour to rotate as the tectonics occurs, building a unique continent, or the Rodinia, in 400 million years. During glacial periods, when sea levels are low, the magma that spreads out from mid-ocean ridges to form virgin oceanic crust wells up thick and fast due to a lesser pressure above. But the production of new crust is stunted in warmer times when sea levels are high. The disappearance of a ice age on a other hand, also is allowing increased mantle melting and volcanism. The development of life increases the level of oxygen, or the Great Oxidation Event, in the atmosphere through the new ability to the photosynthesis which is due to shallow-sea stromatolites, colonies of bacteriae as oxygen is a byproduct of carbon. Such a process further oxydizes some compounds which determine iron ores. Before oxydizing iron ores determined the sea a green color and, after, its usual blue color. Oxygen was present in the oceans 1.5 billions years before marine like as the depths of seas remained devoid of it. The day then passes to 18h. By 750 million years ago, Rodinia parts in two as volcanism starts back, emitting carbon dioxide, ashes and acidic rains; as rocks trap carbon dioxyne, none reaches the atmosphere which in turn is not able to trap solar radiation and heat. The continent also has shut the transportation of heat from the equator to poles through the marine currents. The Earth thus turns into a giant "snowball", with temperatures at -50° C and a 1.8-mile thich ice layer covering our entire planet. That is lasting about 120 million years as volcanoes take back. As ice cannot trap carbon dioxide like rocks had and as the ice layer also increased the heat in the internal Earth's layers, the atmosphere starts a greenhouse effect. Warming and ice melting occurs. As oxygen peroxyde had been manufactured by solar radiation into the ice layers it is released under the form of more oxygen into the atmosphere, with a ratio increasing from 1 to 21 percent. Oxygen in the atmosphere began to increase between 3.5 and 2 billion years ago and eventually reached its current percentage 600 million years with a roller coaster evolution which might hint to a factor other than oxygen-producing bacteria, like evolution of land plants, a surge in oceanic plant productivity occasioned by the thawing of a snowball Earth, changes in plate tectonics leading to more subduction of ocean floor biomass, or the gradual oxidation of terrestrial crust which stopped the possibility to oxidizing consumption of oxygen	Climate is cold with a tendency to warm at the end of the period. A series of intense global ice ages between 760 and 550 million years ago is driving what is called the "Precambrian explosion" of new life forms around or shortly after that time. That modern forms of life all are due to that monocellular cyanobacteries of the type extremophiles managed to survive the snowball episode deep into the seas, which were only those able to strengthen their cellular membrane against frost. From those, multicellular and then today-like shaped forms of life (a head, a tail, a belly, a spinal cord) swiftly emerged then. A asteroid impact at 2.2 billion years ago might have led to transformative climate change events. Impacts generally had a influence upon climate evolution at Earth	Stromatolites formed around living beings, the first traces of which are dated 3.5 billion years ago. More advanced forms of life appear (eukaryotes; unicellular organisms with a nucleus). The most ancient evidence of the passage from procaryotes to eucaryotes was found in Gabon with a date 2.1 billion years, a time when Earth was acidic. Oldest eukaryotes might have given rise to all others. Advanced forms of algae. Protozoa. Then multicellular marine organisms. Small sponges are the most ancient marine fossiles found as they are dating back to 650 million years, likely hinting to that animal life existed -and survived to- 635 million years when the Earth, by the end of the 'Cryogenian', was covered with ice, a episode known like the 'snowball event.' Sponges, which can thrieve low on oxygen, likely participated in various ways into adding oxygen to the depths of oceans. Recent finds are showing that Nature mix and match parts to make a nervous system, which was a fundamental step into evolution, as the more parts, the more results. Comb jellies, with a nervous system quite specific, likely represent the oldest branch of the animal family tree and not the simpler sea sponges. The ice melt, 650 million years ago likely brought nutrients in the oceans and the massive development of algae, providing for the first step of the food chain hence the emergence of advanced forms of life. Dickinsonia lived 558 million years ago, which is before the Cambrian explosion, as they reached about 1.4 yard (1.4 meter) in size when most of living creatures reached a maximum of few lines (millimeters). Dickinsonia might be the ancestors of all current animals. DNA studies showed that all current living creatures originated more than 100 million years before the Cambrian -- well before even Dickinsonia -- but finding the fossils of these creatures, and then proving they are animals, remains challenging. Movement by segmented, bilaterian animals already existed in the pre-Cambrian period as minute Ikaria wariootia which lived over 555 million years ago, is believed to be the first known example of a modern animal and the oldest ancestor of all living creatures	none (recent studies are bringing the proof that terrestrial life appeared as soon as by 2.2 billion years, under the form of minute mushrooms). Muscular organisms were present roughly 560 million years ago	All major mass extinctions which occurred at the Earth are correlated with devastating environmental upheavals, specifically, massive flood-basalt eruptions, each covering more than a million square kilometres with thick lava flows. By 2 billion years ago, it might that a mass extinction occur with the extinction of unicellular beings of the time. As they multiplied too swiftly, they would have endured a vast starvation once they had exhausted most of the nutritious elements available then
PALEOZOIC (or Primary)
Cambrian 540-490 million year ago		Plate tectonics (which exists since the beginning) gives birth to a supercontinent called Gondwana. Vast shallow seas. It's in rocks of this era that the Grand Canyon was carved. Five hundred million years ago, during the Middle Cambrian, Earth's magnetic north and south poles flipped nearly 80 times over a 3-million-year-period as as that turned then to 24 flips and then 1,5 flips, each million years, which likely was due to the decrease of heat exchange between the core and mantle	Climate is mild, with a possible glacial incursion at the end of the period	As life could survive the snowball event deep in the seas, it turns multicellular, and advanced, marine invertebrates. Plants are algae only. That time is called the 'Cambrian explosion of life,' as it constitutes the real beginnings of life, with modern shapes appearing and evolution beginning. That era saw the appearance of all the major animal groups and the establishment of complex ecosystems. A jump in oxygen levels just before or the Darwinian race between animals could explain that explosion. Giant shrimp-like predators dominated the seas as they hunt on the sea-floor under 330 feet of water. The oldest fossil ever found is a 520-million year old athropod sea creature	none	The extinction termed 'Kotlinian' was maybe linked to the end of a turbulent period flips of the Earth's magnetic field
Ordovician 490-443 million years ago		Plate tectonics forms another mass of land	Climate keeps being warm with a tendency to cold at the end of the period. The climate is uniform, with no climate zones. Plants are always mostly algae	Marine life is still the only form of life with the early vertebrates appearing. By that period, Morocco lied at the South Pole of the Earth as it also features the 'Great Ordovician Biodiversification Event.' More advanced animals of the early Ordovician did not immediately replaced the Cambrian creatures, but with a gradual and long replacement instead. At the time shrimp-like top predators of the Cambrian loose to better adapted, strong exoskeleton or sturdy shell and power beak featuring sea scorpions and nautiloids. Trilobites also date back to that era. Another highlight of that era is that some species are splitting from fishes whose bones are made of cartilage into a line of tough-boned individuals about 460 million years ago. Such 'gnathostomes' first looked like armored fishes, or placoderms as they later evolved into vertebrates with jaws like fishes and sharks to birds, reptiles and eventually humans)	primitive land plants? About 457 million years ago by the Ordovician period, a huge volcano outbreak dispersed a 10-yard thick ash layer, might have provided the breeding ground for first land plants. The absence of life on land is due to that solar ultraviolet radiation is freely reaching the surface of the Earth as no ozone layer still is extant	at about 445 million years ago; 12 percent of families, 65 percent of species die; due to large glaciation or sea level fall, or even a gamma-ray burst explosion. Only the marine creatures which lived under a sufficient height of sea survived. Generally it takes about 10 million year for a complete recovery after each mass extinction, , regardless of the size of the latter (recentest studies might hint to better a 1 million years only). The greater diversity of life, after that event, might be due further to an increase in the number of NEOs striking Earth -following the collision of two massive bodies in the asteroid belt- which created a challenge to life and helped for a swiftier evolution
Silurian 443-417 million years ago		Two masses of land exist. One near the equator, and the Gondwana at the southern polar regions	Climate keeps to be warm and uniform, with pockets of aridity in some places	Marine life is mostly invertebrates. Giant marine scorpions. Extensive apparition of coral reefs. Likely the first apparition of sexuated reproduction among some marine vertebrates, between 430 and 360 million years ago at the same time that those beings are getting jaws. Bony and cartilaginous fish have a common ancestor as they split apart around 420 million years ago	Apparition of the very first land plants. They have no leaves. The Earth filled with tropical marshes. Fungi may have had an important role in the colonization of land by eukaryotes
Devonian 417-354 million years ago		More lands are emerging from submersion. Period of intense volcanism	Climate is warm and moist with temperature at about 30° C. More oxygen in the atmosphere as produced by more plants brings that the Earth atmosphere is now reaching its present day composition and could allow humans to breathe	Various forms of fishes exist. That era, generally, is called too the 'Age of Fishes'. It is too at that era that the first fishes (or vertebrates which are called tetrapods) are transitioning from the marine to the terrestrial medium	Life has appeared on land as the ozone layer has formed. Swift evolution of the vertebrates and apparition of the ancestors of modern fishes. First sharks. Very first air-breathing creatures like spiders or centipedes migrate to land as fresh water dipneusts, would have been the first fishes to migrate to land, 400 million years ago. It might that the concurrence in the seas by that time between numerous fish species brought some of those to try terra firma like the place of new opportunities. About 400 million years ago, ancient ancestors of today's dragonflies and mayflies were the first to develop wings. Plants spread over the planet. They have now roots and leaves. Seeds is the way they reproduce as until now vegetal life had through spores only	A mass extinction about 365 million years ago (14 percent of families, 72 percent of species; due to an impactor?). That extinction is also termed the 'Late Devonian Kellwasser event'. That major event was followed, 15 million years later, by the 'Hangenberg extinction', which seems to have been the actual cause of the mass extinction. Then the 'Romer's Gap', during another 15 million years, no more species transitioning to terra firma are seen anymore. The surviving tetrapods are thus at the origin of all the biodiversity on the lands, through the terrestrial vertebrates
Carboniferous 354-290 million years ago		Epoch of the Laurasia, North and the Gondwana, South. Both masses collide, forming large mountain ranges as the landmass settles about the equator. Vast shallow seas. Coal-forming sediments are laid down in vast emerging sea floors, from vast forests	A major climatic change occurs. The weather is cooler and drier, bringing a long glaciation. Atmospheric CO2 levels dropped to modern levels soon after the appearance of woody forests, by 300 million years ago bringing more oxygen and forms of life	Fishes continues to dominate the marine life. Swift development of amphibians. Fossilized rod and cone cells allowing for color vision appeared at least 300 million years ago	Rapid development of insects, some of them gaining wings. First reptiles. Forests. Living beings now reproduce through eggs with a hard shell as until now they were laying their soft eggs under water as terrestrial vertebrates turn to plants in terms of food. Amniotes, tetrapod vertebrates, appeared 330 million years ago as they divided into two branches, one of which gave dinosaurs, current reptiles or birds as the other gave the synapsids, which is the one of current mammals or extincted (among which the dicynodonts, mega-herbivors which features both reptilian and mammalian carachters, and they survived the Permian-Trias extintion; cynodonts are other synapsids)
Permian 290-248 million years ago		A single supercontinent, the Pangea, forms from Laurasia and Gondwana. It's extending from one pole to the other, surrounded by a vast world ocean. Vast deposits of salts. The Panathalassic Ocean was one of both surrounding the Pangea	The climate is hot and dry, with deserts, except in the southern hemisphere where a vast glaciation persists	It's the end of the preeminence of marine life	Development of the land species and of the number of individuals. Insects evolve towards their modern forms. Stupendous sizes attained by insects some 300 million years ago has to do with periods of high oxygen concentrations in the atmosphere, reaching up to some 50 percent richer than today and feeding the oxygen-hundry metabolisms of insects. Despite rising oxygen levels, insects size shrank about 150 million years ago when confronted to the apparition of birds like their predators, and a second time between 90 and 60 million years ago when birds got better at flying. Four-limbed vertebrates becomes more diverse with primitive amphibians, early reptiles and synapsids, a group to include mammals in the future. Reptiles develop swiftly in various forms. To resist to when the climate turns cold, plants and trees turn with falling leaves. Huge herbivores contributed through their waste to the availability of nutrients globally	A mass extinction 250 million years ago -the Permian-Triassic extinction or the 'Great Dying'- (52 percent of families, more than 90 percent of species as algae, mostly, only, survived; that constituted the greatest mass extinction in the history of Earth; due to a impactor (a vast gravity anomaly discovered under the Wilkes Land ice sheet in Antarctica might be linked to the Great Dying) or to large scale volcanism through coal beds (a 'supervolcano' or a chain of volcanoes) in Eastern Siberia, known like the Siberian Traps. Species diversity alreday declined in the 80,000 years leading up to the end-Permian mass extinction, which itself occurred over around 60,000 years. The findings also cast doubt on the existence of a smaller-scale die-off known as the end-Guadalupian, or Capitanian, extinction, which is thought to have wiped out many marine species around 260 million years ago. Waves of extinctions occurred over a time interval of 60,000 to 120,000 years. It might that land plants did not experience widespread extinction compared to marine. Certain plant groups living in harsh environments and enduring seasonal droughts might have survived. Although the oceans buffered the acidifiying effects of carbon release from contemporary pulses of volcanism, buffering failed when volcanism increased during the formation of the Siberian Traps. The result was a widespread drop in ocean pH and the elimination of shell-forming organisms. That event also likely was due to a hot blob of magma which rose from the depths and cracked the Earth's crust. There was a global warming and low oxygen conditions, with sulfur dioxide, acidic rains and more carbon dioxide). A large, 30-mile (48-km) wide meteor might have been at the origin of the extinction, crashing into present Wilkes Land, East Antarctica, further leading to the breakup of the Gondwana supercontinent with a tectonic rift pushing Australia North. The last stroke in the extinction came after a global warming of 5 degrees C occurred, unfreezing large quantitites of methane hydrate from the bottom of the oceans. Lavas coming on contact with methane unleashed fires and more carbon dioxide. Mass extinctions similar to the one of the Permian-Triassic are thought to occur each 300 million years. Consequences of the extinction lasted 80 million years as the existence of the single continent Pangea might have been a factor A middle-Permian mass extinction could have occurred by 260 million years ago, caused by a volcanic eruption that could have taken place in southern Asia. It could have released a large amount of greenhouse gases, specifically carbon dioxide and methane, resulting in severe global warming as it was also a reason for the creation of a dramatic rock formation in southern China known as the Emeishan Traps
MESOZOIC (or Secondary)
Triassic 248-206 million years ago		Few geologic events. The Pangea is always a vast, unique continent. By the end of the period, first rifts begin to break the Pangea apart	Climate is warm, semiarid to arid, turning more moist at the end of the period. With a heat of about 40° C, methane ice which lies at the bottom of the oceans is melting and a greenhouse effect occurs. By Late Triassic, a incredibly dry climate turned wet, and stayed that way for more than a million years, bringing to mass extinctions which could make easy the appearance of dinosaurs. That was the so-called Carnian pluvial episode, which also brought some other evolutional changes (first mammals, modern corals and plankton). Volcanic eruptions likely were responsible for the climate change, mostly occurring from British Columbia, Canada to Alaska, USA	Ichtiosaurs (that Greek name means 'fish lizards' as they lived between 245 million to 90 million years ago). First carnivor species	Earlier dinosaurs might have evolved quicker than thought and might have not been part of the recovery of the preceding extinction event, as too they might not have change ecosystems as much as believed. Permian mass extinction allowed for new niches like to the cynodons, faraway ancestors to mammals which lived underground. A ancestor to mammals likely appeared since the Late Triassic (approximately 208 million years ago) in Laurasia. Early dinosaurs. Common ancestor of birds and crocodilians. Ferns when the climate becomes moister. Very first mammals, evolving from the reptiles. As far as the differentiation between males and females in mammals is concerned, the Y (male) and X (female) chromosomes emerged around 200 or 300 million years ago, in a common ancestor of most mammals. Males and females already existed, but their sex was determined by environmental factors such as temperature, rather than genetics. This all changed when a gene called SRY evolved from a related gene, SOX. The chromosome on which SRY evolved became the first Y, and its former pair, home to SOX3, became the X chromosome, thus laying the foundation of chromosomic difference between males and females. Some species other than man have lost their Y over a long span of time as sex-determining genes have emerged on other chromosomes. There is still debate among scientists to whether that could also be the destiny of the human Y in the next 10 million years or not as a recent study has shown that the human Y just lost 1 gene over the last 25 million years	210 million years ago (the End-Triassic Extinction; 12 percent of families, 65 percent of species die. Due to an impactor and large scale volcanism in Central Atlantic triggered by the Pangaea breaking or the 'Central Atlantic Magmatic Province.' Most recent findings points to that the release of CO2 and sulfates by the volcanic activity triggered in turn the carbon methane release from the ocean floor where it was stocked, as caught like methane ice. That titanic methane release brought to a hotter atmosphere as organisms and ecosystems could not adapt). Changes in the biochemical balance of the oceans at the time were also a critical factor in the extinction
Jurassic 206-144 million years ago		Pangea further splits as tectonics takes on. Since then, plates changed speed and direction over geologically short periods of time of about 1 million years or sometimes increase their average motion, which is of 4 centimeters a year. Vast seas are back, of it the Tethys. Oil forms in those from dead fishes. The Atlantic Ocean forms by 180 million years ago. Formation of thick layers of clay and chalk. Previous mountain ranges have been mostly eroded to hills. That time is a one of stabilization after both the mass extinctions	Climate keeps to be warm, moist with a colder episode -and some subtropical regions- at the end of the period	Ichtiosaurs are roaming the seas and other large predators too. Deep sea might have played a great role in producing and preserving forms in marine life instead that life started in shallow waters and moved deeper	Reptiles everywhere, seas included. Large reptiles appear. Dinosaurs are the dominant ones on land (dinosaurs might have been neither cold-blood nor warm-blood creatures but in-between instead allowing to move, grow and reproduce faster and having a lower food demand, explaining their domination). The rule of dinosaurs was allowed through the creation of the Pangea continent as early, Triassic dinosaurs took 30 millions years to populate the tropics because the region had elevated carbon dioxide levels due to a unpredictable hot and arid climate. By early Cretaceous dinosaurs were more mobile than thought and able to disperse over very large distances, mixing and mingling for much longer as they reached to any continent before those fragmented. The diversity of dinosaurs was linked to the fragmentation of habitats once Pangea fractured into continents. The Archaeopteryx, the first bird, appears. Early birds, as they evolved from other feathered dinosarus through the Archaeopteryx, sported feathers on both their arms and legs and later kept them on their arms, or wings only. Frogs, toads and salamanders are the second generation of amphibians. First mammals are shrew-like beings which live in the forests and have invested the nightly niche to escape their dinosaurian predators (some views state that mammals diversified since that period already). Very first lineaments of flowers at plants and trees. A recent trend is to include climat models into the story of geological eras, which is adding to the understanding of a given epoch The dislocation of Pangea as combined with a increase of temperate moist regions, would have allowed to the swift development of flower plants. Herbivor dinosaur species gave more giant individuals, far more than current species. To turn bigger, to have a larger digestion time brought to a better food/energy ratio thus a genetic advantage. The role usually played by smaller species might have been assumed by young of such large species. That occurrence took place by the end of geological periods which dealt with dinosaurs, which likely matches a stable environment. Carnivorous dinosaurs had, on a other hand, as many smaller species as large ones as their size reached a maximum in terms of benefits. Tyrannosaurs may have hunted in packs to take down large prey, just as wolves do today as they liked to head-bite each other however. Gigantism affected dinosaurs about 200-180 million years ago
Cretaceous 144-65 million years ago		Present shape of continents appears although they are not at their current location. A circum-equatorial sea, the Tethys, form between the northern and southern continents. At 120 million years ago, the Grand Adria continent born 120 million years before, splitting from Gondwana, slipped under current Europe (as it was about of the same size than it). Vast, slow rivers. Tall stacks of chalk layers (the cliffs of Dover, England, date back to this period). New mountain ranges like the Andes or the Rocky Mountains. Subduction of the Nazca tectonic plate at northern Andes began during the late Cretaceous period (around 80 million years ago) and propagated southwards, reaching southern Andes by the early Cenozoic era (around 55 million year ago) thus showing to a discontinuous process. Length of day at the time of dinosaurs was 23 hours. Large asteroid impacts –- more than 0.6-mile across -– went from one every 3-5 million years prior to 90 million years ago, to roughly 1-2 every million years nowadays	Climate is warm, with poles free of ice. Sea levels rise submerging 30 percent of the lands. During the Late Cretaceous (97 million to 65 million years ago), high global sea levels are extant, with North America splited through a interior seaway, into a western landmass called Laramidia and an eastern one called Appalachia. The length of the day still not has reached its current length as it lasts 22 hours only	Marine dinosaurs still. Giant tortoises. Abundance of marine life. It's this marine life which yields the chalky sediments of this epoch. At a time when dinosaurs ruled the land, mosasaurs, a type of swimming reptile related to modern Komodo dragons, came to dominate the seas. Ichtiosaurs might have died 90 million years ago, before their land and air cousins due to a global depletion of oxygen in the oceans, possibly due to volcanism)	It's the apogee of the large reptiles. The dinosaurs are now dominating everywhere. All dinosaur groups rapidly changed size to bigger at the beginning of dinosaur era as that trend slowed quickly. A part of dinosaurs, herbivorous ones mostly, might have been warm instead of cold-blooded like usually thought. Air making up to 60 percent of bones of long-neck dinosaurs, like those of current birds, made easier to those to support such physical features as tendons and ligaments were positioned in a maximizing way. Dinosaurs further could breathe like bird drawing fresh air permanently from their lungs. Pterodactyls. Flying reptiles were social animals living in flocks. Birds turn into those land- and those sea-adapted. Dinosaurs were laying eggs which were partly buried like those of crocodiles, partly hatched like those of current birds. Mammals have turned vivipares as one species grew larger than previous shrews. Early flowering plants (angiosperms), modern (leaves-falling) trees appear. The new way of reproduction via the flowers is linked to the development of the modern types of insects	65 million years ago (11 percent of families, 62 percent of species die). Prior to the KT event, Earth was already under stress. There was a apparent surge of carbon in the planet oceans, likely caused by long-term eruptions from the Deccan Traps and acidifying the oceans. Due to the impactor of Chixculub Crater and to large scale volcanism in Deccan, India, within a 50,000-year timespan, meaning that the impact and the ramp-up in volcanism, were essentially simultaneous and likely linked trough a seismic connection. The impactor was 6-mile (10-km) wide, with a speed of 44,000 mph, as it had originated 100 million years before, from a collision which happened in the Asteroid Belt). This mass extinction caused the disappearance of the dinosaurs with temperatures of 275°.C, giant tsunamis and a nuclear winter to follow, lasting years. Recent studies seem to favour the explanation of this 'K-T' (for 'Cretaceous-Tertiary') disparition by the sole Indian volcanism (it would have sent 10,000 billion tons of sulfur dioxide into the atmosphere as the asteroid would have between 50 et 500 billion tons only and, further, would have hit 300,000 years before the dinosaurs disappeared. It's likely that a plausible explanation be a mix of factors, with an asteroid, volcanism or even a changing climate as changes in climate and landscape reduced the diversity of different plant-eating dinosaurs. Those were further decimated through the impact and the dinosaurs' food chain basis thus extincted. Some dinosaurs managed to survive the demise. The fish version of dinosaurs, as far as they are concerned, went extinct as soon as by 25 million years earlier than the common type, or the 'Cenomanian-Turonian' extinction, with varied sea dinosaurs and one-third of marine invertebrates at it maybe was due to a loss of their ecological niches. Likely darkness triggered by soot in the atmosphere, not cold, wiped out most life on Earth
CENOZOIC
Tertiary
Paleocene 65-55 million years ago		Vast inlands of the Cretaceous dry up exposing more land areas. A remnant Tethys sea is found in the equatorial region. Intense volcanism (lava layers of the Deccan, India, date back to this epoch)	Climate keeps to be warm		As the only survivors of the dinosaurs era, with crocodilians and birds, mammals develop, which survival was due to that they lived underground, had a omnivorous diet and were vivipares, and diversify due to their basic form which they kept along that era, viviparity excepted, hence they are able to adapt to all the new ecological niches which are available in the post-KT world. They spread to most of environments. Of note that the previous Mesozoic history of mammals was approximately twice as long as the Cenozoic's Leave-falling, flower-featured trees and plants spread too after the mass extinction as more able to adapt to a variable environment. The ancestor dinosaurs to birds had evolved smaller which allowed them to survive the KT event through better adaptation to a variety of environments, with four bird lineages lived through the catastrophe and turning into 10,500 species living today
Eocene 56-34 million years ago		India colliding with Asia is creating the Alpine and Himalayan systems. Australia splits from Antarctica. Formation of the African Rift. Tethys is now shallow. A large impact occurred at the time, at 40 million years ago, creating a crater 1,000-foot deep and more than 19-mile wide. Scientists have come to believe that tectonic changes could have brought change in ocean chemistry some 50 million years ago, increasing the oxygen and modifying climate	Climate is subtropical and moist in North America and Europe	Cetaceans (sea-adapted mammals) like the whales or the dolphins appear. Fishes are mostly modern	Ancestors of horses, rhinoceros, camels and of other modern mammals appear. First apes and gibbons in Burma. As Asia at the time is a vast continent with varied weather zones and miscellaneous environments, it is there where the main evolution of mammals occurs, like a answer to such a diversity. The development of an efficient masticatory system allowed early mammals to begin the process of digestion by shearing and crushing food into small boli instead of swallowing larger pieces in the reptilian manner, which necessitates a long, slow and wholly chemical breakdown
Oligocene 34-24 million years ago		Africa closing to Europe are closing the Tethys sea and just leave the Mediterranean Sea as a remnant. More lands appear. Alps are forming	Climate is temperate, with a glaciation beginning in Antarctica. Colder regions in some part of continents	The marine life becomes more diversified (crabs, mussels)	Modern mammals now become dominant. Early primates appear in North America. Early apes in Egypt. Many archaic mammals become extinct. Due to cold in some regions, forests diminish as grasslands expand. Hence a development of grass-heating species (small elephants, giant rhinoceros). As mammals until then were parting into placentary ones and marsupials turn mostly placentary except in South America and, above all, in Australia where marsupials keep extant
Miocene 24-5 million years ago		Modern ocean currents are established. Intense volcanism	Climate is cooler, but mild and moist North. A circum-antarctical current isolates the Antarctic waters as the continent becomes frozen (temperature however along the Antarctic coast 15 to 20 million years ago were 20 degrees Fahrenheit (11 degrees Celsius) warmer than today, with temperatures reaching as high as 45 degrees Fahrenheit (7 degrees Celsius). Precipitation levels also were found to be several times higher than today. When the Earth heats up, the biggest changes are seen toward the poles with a southward movement of rain bands associated with a warmer climate in the high-latitude southern hemisphere. Antarctica looked like present-day Iceland). General drop of sea level. Important rainfalls. Earth now has reached it nowadays shape and climate. It is possible that over eons, dust layering down upon oceans' surface is stimulating the production of microalgae, which are absorbing carbon dioxyde from the atmosphere as they develop. Such a depletion might have reach up to 30 percent by some periods, bringing to a decrease of the natureal greenhouse effect at Earth hence a ice age	Early seals and walruses. Very numerous, giant, sharks	Mammals are mostly modern. Elephants are much taller Higher primates evolve with advanced primates present in southern Europe and Asia. Some coasts are submerged. Grasslands replace forests on vast parts of continents. Climate change, changing sea level and vegetation, may isolate some populations in a given species. Three-toed horses, deer, camel and various species of apes
Pliocene 5-1.8 million years ago		Mountains ranges continue to form or to uplift. Continents and oceans are reaching their modern shape. North, Black, Caspian, and Aral seas form	Climate becomes cooler and drier. The emergence of the Isthmus of Panama cuts ocean circulation patterns, hence the Arctic ice cap forms. Climate ressembles much that of today except with a vaster temperate zone. Atmospheric carbon dioxide levels increased by 120 ppm as that increase took 10,000 years	Marine life reaches its present aspect. Giant sharks disappear	Mammals tend to be larger than those of previous periods, although the number of mammals species is declining. Elephants spread. Late in the period, Australopiths appear in Africa. They are the first link to Homo sapiens. Since around 2 million years ago, when the genus Homo appeared on the scene, mankind might have begun to manipulate its environment on a large scale and bring a broader decline in large-carnivore diversity in Africa, for example
Quaternary
Pleistocene 1.8 million-10,000 years ago (or "Great Ice Age")		Continents are eroded by the glaciers activity. Great Lakes, in North America, form during this period	It is the 'Ice Age.' Ice sheets and glaciers extend or shrink along 4 or 5 alternating glacial periods which are yielded by the Earth's orbit excentricity variation. That epoch will feature a decrease of temperatures and drought in northeastern Asia bringing the decline of subtropical forests existing since 5 million years. At the peak of the Ice Age, 30 percent of the Earth is covered by glaciers as parts of the northern oceans are frozed. Periods of deep cold alternate with periods of heat. It's likely that mankind's emergence might be linked to an unusual run of ice ages. Since 800,000 years ago, nine climat cycles occurred on Earth (until 420,000 years ago the warm periods of those cycles were less warm albeit lasting longer than after that date, when they became warmer and lasting less; during those last 800,000 years interglacial cycles occurred with a period of 100,000 years. Before, between 2.8 and 1.2 million years ago, glacial cycles were less important in magnitude and shorter in duration). The warm ages then brought 4.5°C in more, as the icy ones 10°C in less, as the Arctic and the Antarctic were similarly affected by the cycles. An 'interglacial' age occurred about 120,000 years ago, with the sea level rising by 10 ft in a duration of 50 years only. A 'Last Glacial Maximum' (LGM), 21,000 years ago with temperatures around 4° C. lower than now, and ice sheets covering all of Canada and Northern Europe as a warm period 6,000 years ago, called the 'Holocene optimum' (HO), with temperatures roughly et frac12;° C. higher than now, and plant life flourishing in the Sahara. The 'Younger Dryas', the late cold period of the epoch -precisely a colder episode among a warmer epoch- might well has been caused by a comet impact in northern Canada, about 12,900 years ago, or another impact, at the same time, over Greenland. The impact not only wipped out megafauna and the human, Clovis culture in America but it triggered too a cooling period worldwide. The episode might altogether have been due to the large glacial Lake Agassiz in North America burst its banks and pour into the Atlantic and Arctic oceans, diluting the warm currents circulation, or the so-called 'conveyor belt,' as the cooling occurred in just a matter of a decade, or even one year or too at most and the recover would have taken 100 to 200 years, as that last ice age would have lasted 1,300 years in total as it was followed by a rapid warming. Very high concentrations of dissolved carbon dioxide suddenly appeared in surface waters of the southern Atlantic Ocean and the eastern equatorial Pacific Ocean at the end of the last ice age between 16,000 to 10,000 years ago, as the cause of it is still unknown		Climatic changes that took place at the end of the last Ice Age led to formation of new subspecies. Climate variations are generating new mammals and animals' migrations as 36 percent of species were to disappear 10,000 years ago with the last episode of climate warming. It's the epoch of Homo habilis, the first tool-making man. The last and most advanced man, Homo sapiens, appears by the end of the period. Man encounters large mammals (like the wooly mammoth or rhinoceros, or the musk ox; and hippopotamus and lions during the warm episodes). Megafauna likely disappeared for climate causes (musk ox, woolly rhino) or human ones (steppe bison, wild horse) causes, or both (reindeer population of which however remained stable). The end of woolly mammoth as they had lived during 250,000 years before 10,000 years ago was likely due to climate change, shifting habitats and human hunt by the end. Modern elephants, horses, and cattle appear. Cold periods, due to a decrease of carbon dioxide in the atmosphere, lead to the disparition of numerous plants and trees as the tougher (oaks, poplars ...) only are surviving. It's the tundra which is the main landscape during the colder episodes, as some large mammals, feeding on the disappearing species, may have disappeared consequently in some parts of the world. The transition, generally between the Pliocene and the Pleistocene might have been due to the explosions of supernovae in a relatively close neigbourhood to Earth. A ice age 195,000 years ago likely reduced to some few hundred individuals in Africa the population of Homo Sapiens. A spate of megafauna extinctions took place near the end of the Pleistocene epoch, roughly 50,000–12,000 years ago, when fully modern humans were spreading across the globe, which link is still the object of a debate
Holocene 10,000 years ago-now	It's not known whether our current epoch is a warmer lull of the previous period, or a geologic epoch of itself. It's a warmer period in any case matching the end of the Last Ice Age. Since the last Ice Age 14,000 years ago, Earth climate warmed by 39 to 45 degree F. Ice-sheets are retreating and deserts forming in some areas. Sea level is rising as England becomes an island. Forests are back against the tundra. It's the Neolithic, or mankind inventing agriculture. This took place in the Middle East, in the Indus valley, Pakistan, and in China, which are the first three homes to civilization. Agriculture will be further invented in some other places or it will spread from its earlier homes. Man settles in villages. He then invents states and empires. This evolution leads to the Industrial Revolution 250 years ago, as the modern world is a world of high technology. Some are asserting that, since about 75,000 years ago, a form of mass extinction of the living species -in fact an increase in the regular pace of extinction of those (about 0.25 percent of the species that is)- might be due to the emergence of Homo sapiens, then accentuated during the Neolithics and, at last, by the industrial era, or, more recently still, due to the demographic pressure worldwide. The 21st century might be considered the era when mankind is entering the 'Anthropocene Era,' the epoch when human activities are becoming a defining characteristic of the physical nature and functioning of Earth. The International Union of Geological Sciences (IUGS) has added three ages into the current Holocene epoch, which began at the end of the last ice age, about 11,700 years ago: the Greenlandian age, which marked the start of the Holocene and was a warmer period, the Northgrippian age was a relatively cold stage that began about 8,300 years ago, and the Meghalayan age spanning over the latest 4,200 years of history. The Meghalayan age started with a 200-year global drought

->The Last Word? Really A Asteroid Caused the Dinosaurs Demise!
It might that the debate about what really caused the dinosaurs demise is over now, with a panel of 41 scientists from across the world reviewing 20 years' worth of research, by March 2010. The Cretaceous-Tertiary (KT) event really caused the end of the dinosaurs 65 million years ago through a asteroid hit and wiping out more than half of all species, and the ecosystems, on the planet. The debate usually is confronting the tenants of the asteroid theory against the ones of a strong and 1.5-million years lasting volcanic activity of a series of supervolcanoes in the Indian, Deccan Traps. The study holds for a 9-mile (14-km) wide asteroid which slammed at Mexico's Chicxulub location. The shock triggered large-scale fires, 10 Richter scaled earthquakes and continental landslides which created tsunamis as the impact had a force of a billion times the Hiroshima bomb! The hit also blew material into the atmosphere, creating a global winter further. The evidences were collected from the work of paleontologists, geochemists, climate modelers, geophysicists and sedimentologists. The study concludes that the asteroid theory is the only plausible explanation for such a catastroph as the volcanism in India only affected marine and land life with minor changes during the 500,000 years before the asteroid's hit
The debate, on the other hand, since September 2011, has now passed onto the question of what family of asteroids in the asteroid belt gave birth to the demise asteroid! Astronomers first believed that that was the remnants of huge asteroid Baptistina, which crashed into another asteroid in the main belt between Mars and Jupiter about 160 million years ago. Now they think that that event occurred closer to us, by 80 million years ago only and that none of resulting asteroids had time enough to turn into the KT asteroid. Asteroids normally take numerous tens of millions of years to be nudged into the inner solar system through 'resonances' or areas in the asteroid belt where gravity nudges from Jupiter and Saturn to fling them out of the belt
Dinosaurs also might have pumped out tons of methane in the atmosphere since about 250 million years ago, enough to warm the Earth's climate and hasten their demise. Finds on a other hand, are showing that the world of dinosaurs was dynamic at the time of the asteroid strike, with some herbivores in a slow decline in some regions of the world and thrieving elsewhere, hinted to by the state of their biodiversity as other herbivores and carnivores as a whole were in a time of increasing diversity. A study by 2013 puts the impact and the disparition of non avian dinosaurs events within 32,000 years of each other instead of 200,000 as a changing climate from volcanic eruptions also made life harder for the dinosaurs with temperatures plunging. Mammals generally were more intelligent and can adapt better than dinosaurs
According to last studies by 2019, the KT killer asteroid really existed, wipping out 75 percent of life of the time. After impact, the crater was filled with a 430-foot thick layer of material from the surrounding area or material washed into by a subsequent tsunami. Fires ignited in the area as the tsunami reached to Illinois in the USA. Although the asteroid hit erase 75 percent of life on Earth instantly, most of its effects occurred with a long-lasting global cooling as it mostly marked the beginning of the end for dinosaurs. Not all the dinosaurs died that day, but many dinosaurs did. The impact vaporized about 325 billion tons of sulphur-rich rocks found in that region, into the atmosphere

->A 'Capitanian' Mass Extinction?
Apart from the 'big five' mass extinctions, a sixth one might have occurred 260 million years ago, at the end of a geological age called the Capitanian. A set of ancient volcanic outbursts in China that solidified into rocks called the Emeishan Traps, would have released huge amounts of sulfur and carbon dioxide, potentially causing a quick global chill followed by a longer period of global warming. The gases could have also driven acidification and oxygen depletion in the oceans. The Capitanian extinction, on a other hand, might have been a regional event, or just part of a gradual trend en route to the larger Permian extinction

->What the Traps Are?
Traps are episodes of strong volcanism occurring about each 30 million years. Those overwhelming flows of lava are triggered by so-called 'hot spots' which had been born in the depths of the Earth's interior, which are instabilities of the molten rocks there triggering a massive, localized volcanism above. The last episode of a trap occurred 60 millions years and likely was another cause of the demise of the dinosaurs, with the killer-asteroid just coming to supplement. Traps are also seen like linked to the mass extinction periods

->The Dinosaurs Emerged From the Permain-Triassic Apocalypse!
A find in 2010 in Europe is leading to the idea that the oldest ancestor of the dinosaur lineage found to date, housecat-sized and quadrupedal, emerged as soon as by 1 or 2 million years after the Permian-Triassic extinction as scientists thought that that had occurred 5 or 9 million years later and with no link to the extinction. It looks like that such mass extinctions in fact are playing a critical role in opening niches for new groups to evolve. Bipedality, on the other hand looks like being a late, or evolutionary trait for dinosaurs as those first represented a minute fraction only of the ecological system at the time