Land

Land

The term land , originating in the Latin terra , has several uses and meanings. You can refer to the crumbly material that makes up the natural soil , the land dedicated to the crop or the floor / ground.

Earth is also used as a synonym of nation , country , region or territory : "Nadal was consecrated in his land" , "The men of this land are silent and lonely" .

When written with an initial capital letter, the notion of Earth allows us to name the planetwe inhabit. It is the only planet on which, until now, the existence of life has been proven.

The Earth is located 150 million kilometers from the Sun and is the fifth largest planet in the Solar System . It was formed about 4,570 million years ago and has the only natural satellite : the Moon .

With geoid form (sphere flattened by the poles), the Earth has a diameter of 12,700 kilometers and 71% of its surface covered with water. The specialists have designed two models to refer to the internal structure of the planet: the geostatic modeland the geodynamic model .

The geostatic model establishes three layers: the crust (the most superficial layer, composed by the granite of the continents and the basalt of the oceanic basins), the mantle (the intermediate layer, which reaches a depth of 2,900 kilometers) and the nucleus (the deepest layer, with a thickness of 3,475 kilometers).

The geodynamic model, on the other hand, mentions the lithosphere (the most superficial part), the asthenosphere (which behaves in a fluid way), the mesosphere (also known as the lower mantle), layer D (a transition zone) and the endosphere (which corresponds to the core of the geostatic model).

Documentary and history of the Earth

There is a cinematographic documentary called "Tierra" and it is an exquisite material in which a series of theories converge that allow us to know the actions that the human being has made on the planet and the consequences that they have had on ecology . The material was collected over five years and allows to see the devastation process of a same place over a year; being able to visualize the geographic and climatic changes of more than 200 places in the whole Earth .

It is a work that has been produced by the BBC Natural History Unit, has been filmed absolutely in high definition (HD) and belongs to the television series entitled "Planet Earth", broadcast on the small screen in 2006.

In this work the fundamental protagonists are the polar bears, the African elephants and the humpback whales, species that are in danger of extinction and that, each cycle must face the absence of water, ice or food, increasing every year the risks to lose life, to become completely extinct.

To understand the history of the earth, the different cycles of life have been divided into geological units . They are classified among larger units: composed of eons, which in turn are divided into eras and these into periods. The periods are made up of times and ages. At present we live in the Fanerozoic eon , in the Cenozoic era , in the Quaternary period and in the so-called Holocene period .

The data analyzed by scientists to determine and temporarily divide the different stages are: 

* Extinctions and changes or changes in the fauna and flora (disappearance of species or translation of a group that was settled in one place, to another where its chances of survival are greater); 

* Large episodes of tectonic type (movements in some terrestrial layer that modifies the surface and therefore the survival of flora and fauna that reside in it); 

* Deep changes in the climate (modification of the climatology that causes the extinction or migration of the species towards more propitious spaces, therefore also modifies flora and fauna);

* Important changes in sea level (due to melting or other variations in the composition of the land, can increase or decrease the level of the sea, shortening space for beings living in the area).