sábado, 29 de agosto de 2015

On Geological Time Concept

I have recently been in the heights of the Guadarrama National Park, looking for the beautiful butterfly Graellsia Isabellae... A creature that lives only a few days ... those necessary to procreate and ensure that she and her offspring in successive years continue beautifying, briefly, her world ... and ours.

A world that in Graellsia’s case is so static, in which nothing changes, nothing happens, everything is the same, it is always night ... or it is always summer, and there are always stars in the sky...

Our own life lasts, say, hopefully, eighty years. During that time things do happen, days follow nights, seasons and even some geological phenomena occur, but nothing radical. The Guadarrama range was there when I was born and there will be when I die. The Himalayas continue their ascent and the Strait of Gibraltar is closing, but I've been watching it from Tarifa time and time again, and have not noticed any difference ....

Everest massif from the air..., Lhotse, Cho-Oyu, Makalu...

Physical time corresponding to geological time develops with a slowness that, unlike not just historical time, but own-self time, rather than making seconds, minutes or days to be important, years, centuries and millennia are important.

Earth life resumed in 24 hours

Geology, to the extent that it is a historical science, has in the "time" one of its basic concepts. Its presence is more or less explicit, in the treatment of all geological processes and arguably to have a basic understanding of the science claims to have built the concept of geological time.

Therefore, the importance that the Geological Time subject has in the internal logic of the geological science, along with its difficult conceptualization, justifies its didactic interest. However, didactic treatment of the geologic time is often limited to addressing the difficulty, evident on the other hand, that mental representation offers of such unimaginably great times..
Indeed, the difficulties of magnitude hinder or prevent the construction of the concept of geological time, particularly :
The " imaginative barrier " or difficulty to mentally represent such enormous magnitudes as those involved in geologic time and, 
The slowness, considered from a human time scale, of
most occurring geological processes

Other additional difficulties have to do with the huge spatial and not only temporary scales involved in many of the geological processes, inaccessibility to which these processes occur, the temporal distance between cause and effect and its uniqueness and impossibility to be reproduced in the laboratory.
 Strait of Gibraltar as seen from spanish side

Geological time is but a portion of physical time, the last 4,550 million years, where it makes no sense speaking of the first as a qualitatively different concept from the second.

Ordesa glacial valley, in the Pyrenees (Spain)

The construction of the concept of geological time, to understand the magnitude of the numbers involved, requires first to associate a concept of change. If the Earth is constantly changing, each geological period is likely to be characterized as distinct from the earlier and later. 

In addition, in order to reconstruct the past of the Earth it is not only necessary that changes have occurred but it is essential that terrestrial dynamics have left some kind of remains or evidence of those changes.

In this sense, until the nineteenth century, the teleological and anthropocentric position of the Earth, considered the abode of humanity, left no sense to the existence of a land without men. The concept of an Earth without men was a very important change that was not easy to perform. In the absence in the nature of elements that allow inferring the age of the Earth, it only remained to interpret historical documents and the Bible was not only considered a sacred text for the Christian doctrine, but was generally accepted as the most reliable historical document for earlier periods. 

Genesis was resorting to the more necessary because it lacked alternativeIt is not so surprising Archbishop James Ussher dating the creation of the world at 9 pm on October 23 4004 BC.

In the nineteenth century Buffon estimated the time needed to consolidate the planet 117,000 years, while the total time to get the current temperature would be three million years ... These numbers may seem ridiculous now, but eventually meant a long shot that broke the barrier set by the still dominant biblical chronology and, above all, meant that the age of the Earth could be scientifically calculated.

In the second half of the nineteenth century a number of proposals would happen that aimed to put figures to the age of the Earth. One was due to Darwin, who attributed the age of 300 million years in southeast England, this being taken by others as the "new standard" on the age of the Earth.

But the most influential of these in the second half of the nineteenth century was due to Lord Kelvin, who started from the hypothesis of a land formed by the collision of meteorites that as a result of these impacts, should have been found melted in full. 

From then until now, the planet would have been continually losing heat. In 1868, after some less precise proposals for the Earth he established an approximate age of 100 million years. This figure remained a point of reference for the rest of the century.

Sorrosal cascade spot, Huesca (Spain)

We will not extend here in the further evolution of earth sciences, currently however the age considered for the Earth is more than 4500 million years. That would be today the length of Geological Time for our planet.

Tomorrow, geological time can refer to the geo-planetology and spread in who knows how many billions of years.

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