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Earth History

1. Precambrian

The Precambrian contain the first three eons of the history of the Earth (Hadean, Archaean and Proterozoic).

The formation of the Solar System lasted millions of years.

Asteroids are remnants of the formation of the solar system. Meteors from the asteroid belt give us information about the age of the planets, even the Earth.

The fusion of the Earth divided the planet into two parts:

 

One metallic, dense. It went into the interior of the Earth, creating the nucleus.

Another made by rock. It became the mantle.

 

Hadean

 

It started when the Earth was already formed. It ends when the first life forms appear, the stromatolites. The stromatolites are the eldest evidence of life in the Earth, 3.6 billion years ago.

Most important events:

 

Moon formation. It was created when a small planet crashed with the Earth.

Degasification of the mantle. This fact created a primitive atmosphere, composed mainly by CO2 and water steam.

Creation of the hydrosphere and the start of the water cycle.

 

During this period the hydrosphere and the atmosphere were formed. Nevertheless there wasn't any oxygen at the atmosphere. This implied there wasn't any ozone layer too. This lack of ozone implied that ultraviolet radiation arrived to Earth surface with strong violence. During the last times of this period, it appeared life, only bacterium, although tons of meteors crashed into Earth as well.

 

Archean

 

Life started at oceanic ridges. Nowadays, there are still bacterium related to Earth's first settlers. The hydrothermal activity provided to those forms all their needs, energy, nutrients ...

Most important events:

The meteoritic bombing stooped, so the bacterium could colonize the upper layers of the ocean.

Apparition of the photosynthetic bacterium. These organisms produced oxygen as a waste.

The CO2 concentration fall spectacularly, since this gas is used during the photosynthesis.

High uprising of N2 concentration at the atmosphere. The decomposer organisms favoured this phenomenon.

The atmosphere had already O2 but lower quantity than today.

 

Proterozoic

 

Most important events:

The ozone layer started to develop. The atmosphere had one hundred times more oxygen than today in order to create that layer.

Pluricellular life started to grow. This first animals were similar to sea-worms.

Creation of Rodinia, a supercontinent formed by all current continents.

 

2. Paleozoic.

 

 

It is divided into six periods: the Cambrian, Ordovician, Silurian, Devonian, Carboniferous and Permian.

Geological events in the Paleozoic

 

Rodinia was split. The continents were dispersed and were drifting throughout all the Paleozoic. Towards the end of this era, they became to meet again to form the supercontinent Pangaea.

Panagea began to form during the late Carboniferous. The continental collision led to the creation of the Varician orogeny.

There was a global desertification and an intense erosion of the Varician orogeny as a result of the formation of Pangea.

An intense volcanism occurred during the late Permian, released large amounts of CO2 in the atmosphere and it caused global warming.

During the Carboniferous, huge quantities of coal were created. It also appeared forest of ferns.

 

The biosphere of the Paleozoic.

 

The beginning of the fanerozoic eon is identified on the rocks by the appearance of a great variety of fossils of many different kinds of organisms. This diversification is so quick that it has been given the name of great biological explosion.

Between the Cambrian and the Ordovician the main groups of invertebrates (sponges, annelids, arthropods, etc) appeared.

In the Ordovician period the Agnatha (ancestors of vertebrates) came. Today the only representatives of this group are the lampreys.

In the Silurian the fishes appeared.

Colonization of the Mainland: first by vegetables and after by the animals.

Toward the end of the Permian it happened the biggest extinction in Earth history.

3. Mesozoic.

 

 

It is divided into three periods: Triassic, Jurassic and Cretaceous.

It is characterized by a hot and humid climate all over the planet, which favoured a large diversification of flora and fauna.

There is no glaciation, even in the Antarctic were developed large areas of forests.

Geological events in the mesozoic era

 

Rupture and disintegration of the continent Pangea during the mesozoic era, which originated the current continents.

During the Jurassic, the Atlantic Ocean started to open, which continues today.

Impact of a large asteroid, ten kilometres radius, against the land. This determines the end of the mesozoic.

 

The biosphere in the mesozoic era

 

The hot and humid weather that settled on the planet in the middle of the Triassic, along with the disintegration of the supercontinent Pangea, provoked a great diversification of life and the appearance of very complex ecosystems.

The ammonites were expanded to all the seas.

In the Triassic, reptiles began a quick diversification and conquered all the terrestrial and aquatic environments. A group of reptiles, Arcusaurus, gave rise to dinosaurs. It also appeared the ancestors of mammals.

In the Jurassic birds appeared. Also flying reptiles arose, the pterosaurs, and marine reptiles, for example Plesiosaurs and ichthyosaurs.

Forests of conifers.

First Angiosperms.

During Cretaceous, social insects appeared.

The mesozoic era ended with a great biological extinction, caused by two factors: an intense volcanism and the impact of a large meteorite.

4. Cenozoic.

It is divided into two periods: Tertiary and Quaternary. Its main features are the restoration of ecosystems after the disaster at the end of the mesozoic and the return of the glacial conditions.

Geological events in the Cenozoic

 

Formation of the isthmus of Panama, connecting the South American and North American continents.

Development of an ice cap at the South Pole 35 MA ago. At the North Pole this glacial period was quite later. Glaciation has periods of colder (glacial periods) and warmer periods (interglacial periods) between them.

The Iberian plate move to the Northeast, colliding with Europe and forming the Pyrenees.

The Alboran microplate collided with the Iberian plate and formed the baetic mountains.

The volcanic activity in the Atlantic gave rise to the Canary Islands.

There was a beginning of rifting in the Mediterranean coast that separated the Balearic Islands on the Iberian Peninsula.

 

The biosphere in the Cenozoic

 

Mammals, the ancestors of which were already in late Triassic and developed during the mesozoic era, diversified enormously, and moved to occupy the ecological niches that corresponded to the reptiles.

The birds also diversified a lot and occupy the air habitat. Previously, they had to share it with the pterosaurs.

Herbaceous plants are developed.

Some insects establish a relationship of mutualism with flowering plants.

In the African savanna appeared the first hominids.

During the last three centuries, the human being has developed the technology in such as huge speed that has caused mass extinctions in the biosphere. This extinctions are comparable to the one produced by the meteoritic impact during late Cretaceous.

  

 

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