Geological History of The Earth

The subdivisions of time in geology

The 4.5 billion years of the Earth were divided into three periods, eons:

The Archean going training of the world up to 2600 million years.

The following Proterozoic Archean and ends around 570 million years, it is the period of unicellular life.

The Phanerozoic which begins with the appearance of multicellular life and is not finished yet.

These subdivisions, quite old, are abandoned to the notion of age:

The Precambrian era that matches the Archean and Proterozoic,

The Primary or Paleozoic era: from - to 570 - 240 million years, it is at the level of the evolution of life, the water outlet of living beings,

The Secondary or Mesozoic era: from - to 240 - 65 million years, it is the conquest of all backgrounds through life,

The Tertiary or Cenozoic era: from - 65 to now, it corresponds to mammalian development and the appearance of man. This latest evolutionary stage (started there are 4 million years) had resulted in the definition of the Quaternary period, which seems increasingly regarded as a subdivision of the Tertiary era.

The characteristics of each era are actually much more important and will be considered in more detail in the following pages.

Periods covered by eras is very long, we divided them into periods, or periods (they are represented on the geological scale).

These periods were also divided by floors: each floor is characterized by a certain population of fossils and usually a great cycle of transgression / regression. It is defined in a given place, characteristic of the floor, the type section, which usually gives it its name. For example Oxfordian was defined by a type section located at ... Oxford, Albian as close to the river Aube, the Lutetian in Paris (Lutetia) ... The type section is generally in a sedimentary basin.

The stages were even subdivided to take account of regional differences. These are the areas or having a characteristic nous biozone.

Here is the complete stratigraphic:

                                                                                                                    Precambrian

It is the largest geological period, it represents almost 80% of Earth history. The vestiges of this time are concentrated in cratons different continents.

Despite the small amount of "untouched" land that time, there can be defined several phases:

Permobile a phase or Archaean (the formation of the globe to 2.5 billion years):

This is the stage where the crust is still very mobile due to strong convection currents. The appearance of water in the liquid state already allows the formation of sediment. Metamorphism is strong and there is a large production anatexie of granites that by accumulating lighten the crust (density is low).

Continental crust as we know it begins to form by vertical accretion phenomena and sediment accumulation in the cups.

A transition or lower Proterozoic (from 2.5 to 1,600,000,000 years):

A peripheral phenomenon accretion gradually transformed most stable blocks crusts foreshadowing future continents.

A phase of introduction to plates or Proterozoic average (from 1600 to 900 million years):

The first true open oceans, mountain ranges rise (orogeny Cadomian).

The Upper Proterozoic (900 to 570 million years):

The continental blocks come together as a supercontinent, the Rodina (about 650 million years), and then begin to separate into several large landmasses:

Laurentia, incorporated Canadian shields, Greenland and Hebrideans (North of Scotland and the Hebrides islands) and the North American platforms,

The Baltica, consisting of Europe and North Shields Russian

The Siberia, consisting of the Siberian shield

The Kazakhstania, contituée by the shield of Kazakhstan

China, made by Chinese and Indonesian shields

The Gondwana which meets shields and platforms throughout the Southern Hemisphere.

This huge continent is separated from the other three by an ocean, the Mesogean. The Iapetus Ocean separates him Laurentia and Baltica..

The Paleozoic

Marked by two orogenic cycles, Caledonian and Hercynian, the Paleozoic is divided into two different periods: the Lower Paleozoic and upper Paleozoic.

The Lower Paleozoic

This is the period from 570 to 400 million years, thus covering the Cambrian, Ordovician and Silurian. This period is marked by the separation of supercontient Precambrian and the Caledonian orogenic cycle.

The Lower Cambrian continental shelves are numerous (continents are separated). The marine fauna is therefore growing much because of the many ecological niches available. It thus appears the first animals to shell and shelled. The warm climate of the Cambrian is conducive to this change (after a glacial stage late Precambrian). At the end of the Cambrian tectonic movements seem to announce future Calédomienne orogeny, or match the last gasps of the Pan-African orogeny (African equivalent of the orogeny Cadomian). The France suffers in all distension movement (it is occupied by two oceans).

In the Ordovician, the Iapetus Ocean began to close, while a Rheic ocean off a piece of Gondwana towards Laurentia, Avalonia's. It follows the training of several microcontinents:

Gondwana separated by ocean Rheic,

separated from Laurentia by the Iapetus Ocean,

Baltica separated from the sea Tornquist.

A phase transgressive brand Ordovician, life diversified and appear large groups of animals inverterbrés. Vertebrates are not yet represented by the Agnatha. A glacial climate settles at the end of the Ordovician as Gondwana is then located at the South Pole. The paleontological crisis which marks the boundary between Ordovician and Silurian is certainly related to it.

The volcanic arc that formed early in the subduction of the Iapetus collided with Laurentia. This is the Taconic phase with which stands the calédomienne chain. Some microcontinents of Avalonia participate.

During the Silurian, Gondwana gradually back towards the North while Iapetus is reduced more and more. A transgressive stage on all continents followed. The fish are diversifying, graptolites know their heyday. The collision between Baltica and Laurentia takes place at the end of the Silurian erecting chain Calédonides. The collision has formed this continent is called the Old Red Sandstone or North Atlantic continent or Laurussia. It is roughly the current North America, over Scandinavia. The first vascular land plants are contemporary of the time. The ocean Rheic then reached its maximum aperture. Europe held the Ardennes phase, corresponding among others to the closure of the ocean Massif Central (then separated France in two along a NE-SW axis). We observe its subduction at the Armorican (in fact it would be more accurate to speak of Moldanubian zone). The Caledonian fold will give tablecloths verging North, resulting in the thrust sheet of Brabant of Aboriginal and break the South in the Ardennes.                                                                                                The Upper Paleozoic

This period ranges from 400 million years to 245 million years. It therefore represents the Devonian, Carboniferous and Permian.

At the beginning of the Devonian, all the oceans is closing. In Europe, while the ocean Massif Central is already terminally subduction phase (early flaking is observed), the ocean between Rheic in turn subduction. The Armorican Massif (actually Moldanubian area including mainland is represented by the block forming the Cadomian Armorican) is limited by two subduction zones. Regarding the North Atlantic continent, the Caledonian chain undergoes a significant erosion. These are the large amounts of detrital sedimentary material, from the démantellement chain, which gave the name to this continent: the old red sandstone (old, because there will be later formation of another continent rich red sandstone). The sub-desert climate is responsible for the red color, reddening by deposits.

The collision of Gondwana with the Armorican block is the éovarisque phase. It is the origin of the formation of the Massif Central in France. The Armorican is not yet affected by the compressive phase and undergoes carbonate sedimentation. In the Ardennes, there is instead a distension phase by subsidence. The transgression that follows covers the ancient reliefs. During that phase, the Avalonian microcontinents collide with the North Atlantic continent and complete training appalaches (which is the Acadian phase).

It was towards the end of the Devonian, that really begins orogeny Hercynian (or Variscan). The subduction of the ocean Rheic coming to an end, it becomes even obduction armoricain on the block. The first chipping form on the continent Old Red Sandstone. This is the Breton phase. Regression affects the Ardennes and the Armorican Massif. The latter, as well as the Massif Central, undergoes extensive magmatism. In the Vosges is a submarine volcanism that is taking place.

The Lower Carboniferous (Visean), held the Sudeten phase. The Armorican Massif is then sandwiched between Gondwana in the South and the North Atlantic continent. If he himself is unaffected (it only undergoes surface folds), the Gondwana margin and the North Atlantic continent suffer the contrary cleavage increasingly large that extends inland. For each of these two continental blocks, the front of the Hercynian chain is formed by bending basins are deposited flyshs and where applicable a distension of volcanism. These areas correspond to the north rhénohercynienne area (South of England, Belgium, northern Germany) and saxothuringienne, slightly more internal (Paris Basin, Vosges, South Germany) and south to the Iberian area. The thickening of the Hercynian chain, linked to the stacking of crustal scales is accompanied by the establishment of infracrustaux granites.

Great transgression occurs. Large thrust sheets form in the Southern Vosges, are associated granites anatexie. Maximum compression in the late Carboniferous (Asturian phase)

Late Carboniferous, a compression phase (Asturian phase) causes a fracturing of Europe, according to slip faults NE-SW and NW-SE. It is among other things responsible for the formation of coal furrow and the North Pyrenean Fault (Iberian Block Sliding along the European bloc). The Hercynian Europe is emerged and is the site of a continental lake sedimentation limnique but also marine in the coal furrow in the Massif Central. The vegetation is so lush (France is then located at the equator). This is the culmination of ptérydophytes.

The suture between the European bloc and Gondwana will be complete only after the intervention of a final compression phase, the saalienne phase, which ends in early Permian.

During the Permian, the Hercynian chain is eroded in a desert climate. The large deposits of detrital sediments similar to those formed when démantellement of Caledonian chain. That's why we talk to these continents of New Red Sandstone. Reptiles dominate alors.C'est at the end of the Permian that all the continents meet welded through the collision of the Angara (Ural orogeny) with the other two continental masses, Gondwana and Laurussia already joined. A new supercontinent just formed: Pangea. Located at the equator, within continents turns into desert, this fact, combined with the decrease continental shelves and a generalized regression explains why the end Permian extinction has seen more than 80% of species alive at that time. Northern Europe is invaded by a cold sea while to the south lies the Tethys, warm ocean, which opens to the east. From the Permian means extensional regime is being established by replay slip faults by normal faults, the large sedimentary basins form French (Paris Basin, the Aquitaine basin).                                                         The Mesozoic

This era extends from 245 million years to 65 million years. There are three major subdivisions: the Triassic, Jurassic and Cretaceous. Here are the main features. The history of French regions takes them further.

The Trias

It is a fairly quiet period. The sandstone sedimentation, begun in the Permian continuing on the continents, often referred to also as Permotrias the boundary between the two periods is blurred. A continental basaltic volcanism is however witness the extensional forces excercise this supercontinent.

It is because of this extensional regime that will open the Tethys. This ocean will gradually spread the gondwana of the Eurasian Plate. This separation of Pangaea will be from East to West.

The formation of a rift and then from coast causes subsidence of the continental margins. Thus Téthys will cover more and more continents as a slow transgression. France will be almost entirely submerged in the late Triassic, leaving only its massifs. But at the current Alpes is set up plunge pool, dependence of Tethys, whose warm waters are related to the Paris basin that receives it, cold water from the north. Through Trias will take place originally a regression of evaporite deposit. Then transgression takes to Triassic and is also reflected in the evaporite deposit. These lands play an important role in subsequent tectonic.

After the Permian crisis, diversication of living species is quite large. On the continents gymnosperms develop large forests, it is possible that angiosperms have made their appearance at that time. The insects are now fairly semblabes to existing groups. The first mammals are already developing. Reptiles colonize most environments.

collapse ditches formed Gondwana and evolve rifts. A narrow ocean opens in Gondwana, it enables the end of the Triassic, the separation of African-American unit of the Indo-Australian block. The Indian Ocean then opens between India and Australia. Madagascar also landed in Africa. Another rift zone, still "immature" announces the upcoming opening of the Atlantic. These different blocks, although some individual fields remain no less close. Gondwana still form a huge landmass.                                                                             Jurassic

The opening of the Tethys is increasing westward, as she begins to subducter the Northeast (at the Asian plates). The Middle Jurassic Tethys, in the form of a ridge, completely separated Pangea into two: Gondwana in the south and the north Laurussia. An extension of this ridge forms the central Atlantic where there is a beginning of oceanization. A new transgression phase affects the whole of France, where only a few regions have emerged (Armorican, Ardennes, Massif Central and the Briançon area alpine basin). In Jurassic ago GREG in France, due to the rise of Africa to the north and compression affecting the Tethys. This causes abortion of the Alpine ocean and flyshs training in this area.

Birds begin to appear in the sky, the Dinosaurs are needed them on land and in the oceans pliosaurs. Angiosperms coexist with gymnosperms.

Gondwana at the opening of the oceans is also increasing. India begins to drift towards the North East with the opening of the Indian Ocean, Madagascar is still related. The Jurassic, with the subduction of the Pacific begins the formation of the Andes and the Sierra Nevada on the American continents.                                                                                        Cretaceous

Tethys subducts the South, against the African plate goes, and north against the Asian plate. The Atlantic is first opened in the South, and it separates Africa and South America. Communication between Tethys and Atlantic closes. Tethys then foreshadows the future Mediterranean. The first folds are felt in the Alps. Around mid-Cretaceous, they are thrust sheets that are taking place as a result of peeling of the internal domain. These folds are reflected in Provence whose northern region emerging. This isolates the isthmus Durancian alpine ocean, a branch of Tethys, the Atlantic influence.

The transgression that began in the early Cretaceous reached its peak in the early Cretaceous. It affects all continents. At the end of the Cretaceous, the start of the Alpine orogeny leads to regression of the sea on the French territory.

The Americas begin to approach. India continues to drift towards the Asian plate while Madagascar lies off Africa. Towards the end of the Cretaceous begins to open the North Atlantic. This opening completes the closing movement of the Tethys. It also entrîne sliding of the Iberian plate against the European plate, which begins building the Pyrenees. Each continent is almost out of place on the world map.

The late Cretaceous was marked by a major extinction of living species. The hypothesis of an asteroid impact is now confirmed by the location of its crater off Mexico. The influence of climate is going on cooling during the Cretaceous also to participate in the extinction of some species.                                                                                                                                   The Cenozoic

This era extends from 65 million years ago, until today. It is subdivided into Paleogene, Neogene and Quaternary (previously considered a wholly era).

The Paleogene

This period is also called Nummulitique because of the presence, only in this period, a group of foraminifera: the Nummulites.

The Alpine orogeny peaked during this period. The Alpine ocean gives way to subsiding basins fed high Molasse sedimentation. The webs of chariages, from peeling the internal domain, continue their westward movement. The Pyrenees, Provence but also the Moroccan Atlas and Algerian experience on their side of the peak compression. The areas activated setbacks in Provence will be included in subsequent distension. Indeed, while the maximum compression is at the heart of the Alps, the peripheral regions undergo a distension phase which involves the formation of a molasique périalpin furrow and many ditches collapses (limagne, drill, Bresse, Ales) which receive then an evaporite sedimentation or lake. At the end of the Oligocene, a rift develops between the Corso-Sardinian block and the Eurasian plate.

At the end of the Paleogene, the North Atlantic is fully open and thus isolated North America to Eurasia. A communication channel between the two continents remains possible between Alaska and the Urals. The subduction of the Pacific continues and causes intense deformation in the Andes and the Sierra Nevada.                                                Neogene

The North Atlantic expansion causes displacement of Eurasia to the South-East while Africa goes. Tethys is doomed. Final closure allows significant evaporite deposit in the Mediterranean and the formation of brackish basins bordering the continents, relics of the ancient ocean. The outer areas of the Alps in turn undergo the effects of compression and implement subalpine chains and the Jura. Gradually the chain rises to its current altitude because of isostatic adjustment. After a phase emerged in the Paleogene, Provence is again flooded with water due to the advance of alpine Molasse groove.

The rift that separated the Corso-Sardinian block begins to form oceanic crust. This microplate pivots toward the South into its current position to the end of the Miocene. The opening of this ocean is rapidly Arrested by the Alpine orogeny.

India collided with Eurasia, orogeny ensuing form the Himalayas. Red Sea begins to open. The Andes and the Sierra Nevada undergo large vertical movement behind the establishment of ponds that have given the highlands. The subduction of the Caribbean plate allows the welding of the two Americas. Marsupials that had developed in South Africa will be decimated by the invasions of placental mammals from North America. In Africa, the first Australopithecus leave their footprints on the floor.

Quaternary

This latter period is mainly characterized by the glaciations and the appearance of man. Each ice age is associated an important phase of regression. Glaciers related thereto have shaped the landscape as we know them.

Man evolves and colonize all backgrounds. It is that there are 10 000 years happens to master agriculture and begins to form real companies.