The Earth changes |
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1.-Our planet's age:
From time immemorial, we had explained Earth's evolution as if it was the desire of a divinity, trying to figure out the mysteries of Nature. Some of the first scientifical theories the humans drew up were:
- Catastrophism: this theory explains the formation of rivers, mountains, seas... as a series of natural disasters.
- Uniformitarialism: it says that geologic changes are continuous and imperceptible.
- Principle of actualism: this principle, enunciated by Charles Lyell, propounds that biologic and geologic processes have acted on our planet in the past in the same way they act nowadays.
- Neocatastrophism: it explains Earth's evolution as a slow and continuous process that can suffer sudden changes.
Thanks to the new techniques the human being has developed, the age of our planet has been estimated in about 4600 million years.
2.- Dating Earth's age:
Nowadays we use two methods for dating our planet's age:
- Methods of absolute dating: these allow us to know the age of geologic processes.
- Study of glacial varves: varves are pale and dark sediments formed by the debris of materials inside glaciers.
- Dendrochronology: it consists of studying the rings in the tree trunks. It only allows us to date recent materials.
- Radiometric methods: it's a technique used to date materials, based on a comparison between the amount of a radioactive isotope (knowing its decay rate) and the non-radioactive materials in which they get transformed.
- Methods of relative dating: these methods allow us to know the order in which geologic processes took place.
- Principle of succession of geological phenomena: according to this principle, a geological phenomenon is subsequent to the materials and/or phenomena wich are affected by it.
- Principle of faunistic succession: this principle enunciates that, if we know the age of a fossil, we can know the age of the strata in wich that fossil was found.
- Principle of succession of strata: it was enunciated by Nicolaus Steno in 1669. He thought that new strata are always located on older strata, if these last ones have not been deformed. The strata whose layers have been deformed are known as "non-concordant" strata, and the union zone between two non- strata series is denominated "discontinuity".
3.-The origins of Earth and Universe:
According to the Big Bang theory, around 13800 million years ago, the Universe was compressed in a singularity that exploded, releasing an enormous amount of energy, and originating time and space. Matter particles began to merge,
forming the first hydrogen atoms. Later, our Solar System formed from a nebula composed of gas and cosmic dust that started spinning and acquired a disc shape (with a spherical center). The Sun formed from the center of this nebula, and the planets appeared from the dust located outside the center ball. A process called gravitational differentiation, which allowed the heaviest materials to descend towards the planet's core due to the gravitational force, the took place inside the Earth. Finally, the litosphere solidified and released the gases that were part of the magma.
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