earth's-crust

Louis Agassiz - Earth’s Crust with the Evolutionary History of the Species, “Comparative Physiology”, 1851.

This diagrammatic history of life, proposed by Swiss-American naturalist Louis Agassiz, is very different from Darwin’s. Agassiz, an opponent of Darwin’s theory of evolution, shows the beginning of time as the center of a circle and the present day as the perimeter. According to a divine plan, different groups of animals appear in the various “spokes” of the wheel and then go extinct. Humans enter only in the outermost layer, and at the top, as the crowning achievement of all Creation.

WATER IN “THE GENESIS ROCK”

About 8 years ago, a research group led by Brown University reshaped our understanding of the formation of the moon. Those researchers measured samples from the Apollo missions and found that the rocks…igneous rocks that had been erupted on the surface…actually contained measurable amounts of water.

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Earth may have underground ‘ocean’ three times that on surface

Melissa Davey, The Guardian, 12 June 2014

After decades of searching scientists have discovered that a vast reservoir of water, enough to fill the Earth’s oceans three times over, may be trapped hundreds of miles beneath the surface, potentially transforming our understanding of how the planet was formed.

The water is locked up in a mineral called ringwoodite about 660km (400 miles) beneath the crust of the Earth, researchers say. Geophysicist Steve Jacobsen from Northwestern University in the US co-authored the study published in the journal Science and said the discovery suggested Earth’s water may have come from within, driven to the surface by geological activity, rather than being deposited by icy comets hitting the forming planet as held by the prevailing theories.

“Geological processes on the Earth’s surface, such as earthquakes or erupting volcanoes, are an expression of what is going on inside the Earth, out of our sight,” Jacobsen said.

“I think we are finally seeing evidence for a whole-Earth water cycle, which may help explain the vast amount of liquid water on the surface of our habitable planet. Scientists have been looking for this missing deep water for decades.”

Jacobsen and his colleagues are the first to provide direct evidence that there may be water in an area of the Earth’s mantle known as the transition zone. They based their findings on a study of a vast underground region extending across most of the interior of the US.

Ringwoodite acts like a sponge due to a crystal structure that makes it attract hydrogen and trap water.

If just 1% of the weight of mantle rock located in the transition zone was water it would be equivalent to nearly three times the amount of water in our oceans, Jacobsen said.

The study used data from the USArray, a network of seismometers across the US that measure the vibrations of earthquakes, combined with Jacobsen’s lab experiments on rocks simulating the high pressures found more than 600km underground.

It produced evidence that melting and movement of rock in the transition zone–hundreds of kilometres down, between the upper and lower mantles–led to a process where water could become fused and trapped in the rock.

The discovery is remarkable because most melting in the mantle was previously thought to occur at a much shallower distance, about 80km below the Earth’s surface.

Jacobsen told the New Scientist that the hidden water might also act as a buffer for the oceans on the surface, explaining why they have stayed the same size for millions of years. “If [the stored water] wasn’t there, it would be on the surface of the Earth, and mountaintops would be the only land poking out,” he said.

Newly discovered layer in Earth's mantle can affect surface dwellers too

Hauke Marquardt, Bayreuth University

Sinking tectonic plates get jammed in a newly discovered layer of the Earth’s mantle – and could be causing earthquakes on the surface.

It was previously thought that Earth’s lower mantle, which begins at a depth of around 700 km and forms the major part of the mantle, is fairly uniform and varies only gradually as it goes deeper.

However, our new study points towards a layer in the mantle characterised by a strong increase in viscosity – a finding which has strong implications for our understanding of what’s going on deep down below our feet.

The deep unknown

The Earth’s mantle is the largest shell inside our planet. Ranging from about 50 km to 3000 km depth, it links the hot liquid outer core – with temperatures higher than 5,000K – to the Earth’s surface.

The movement of materials within the Earth’s mantle is thought to drive plate tectonic movements on the surface, ultimately leading to earthquakes and volcanoes. The mantle is also the Earth’s largest reservoir for many elements stored in mantle minerals. Throughout Earth’s history, substantial amounts of material have been exchanged between the deep mantle and the surface and atmosphere, affecting both the life and climate above ground.

Because mankind is incapable of directly probing the lower mantle – the deepest man-made hole is only around 12 km deep – many details of the global material recycling process are poorly understood.

We do know, however, that the main way materials are transferred from the Earth’s surface and atmosphere back into the deep mantle occurs when one tectonic plate slides under another and is pushed down below another into the mantle.

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A strong increase in the viscosity leads to a stiff layer which catches sinking slabs Hauke Marquardt

A trap for sinking plates

So far most researchers assumed that these sinking plates either stall at the boundary between the upper and lower mantle at a depth of around 700 km or sink all the way through the lower mantle to the core-mantle boundary 3,000 km down.

But our new research, published in the latest online issue of Nature Geoscience, shows that many of these sinking slabs may in fact be trapped above a previously undiscovered impermeable layer of rock within the lower mantle.

We found that enormous pressures in the lower mantle, which range from 25 GPa (gigapascal) to 135 GPa, can lead to surprising behaviour of matter. To picture just how high this pressure is, balancing the Eiffel Tower in your hand would create pressures on the order of 10 GPa. These pressures lead to the formation of a stiff layer in the Earth’s mantle. Sinking plates may become trapped on top of this layer, which reaches its maximum stiffness at a depth below 1,500km.

Under pressure

We formed this conclusion after performing laboratory experiments on ferropericlase, a magnesium/iron oxide that is thought to be one of the main constituents of the Earth’s lower mantle. We compressed the ferropericlase to pressures of almost 100 GPa in a diamond-anvil cell, a high-pressure device which compresses a tiny sample the size of a human hair between the tips of two minuscule brilliant-cut diamonds.

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A diamond-anvil cell compresses a tiny sample under high pressure between two minuscule diamonds. Image via Hauke Marquardt, Author provided

While under compression, the ferropericlase was probed with high-energy x-rays to investigate how it deforms under these high pressures. We found that the ability of the material to resist irreversible deformation increased by over three times under high pressures.

These results were used to model the change of viscosity with depth in Earth’s lower mantle. While previous estimates have indicated only gradual variations of viscosity with depth, we found a dramatic increase of viscosity throughout the upper 900 km of the lower mantle.

Such a strong increase in viscosity can stop the descent of slabs and, in doing so, strongly affect the deep Earth material cycle. These new findings are supported by 3-D imaging observations based on the analysis of seismic wave speeds travelling through the Earth that also indicate that the slabs stop sinking before they reach a depth of 1500 km.

Surface effects

If true, the existence of this stiff layer in the Earth’s mantle has wide-ranging implications for our understanding of the deep Earth material cycle. It could limit material mixing between the upper and lower parts of the lower mantle, meaning mantle regions with previously different geochemical signatures stay isolated in separate patches instead of mixing over geologic time.

What’s more, a stiff mid-mantle layer could also put stress on slabs much closer to the Earth’s surface, potentially acting as a trigger of deep earthquakes.

We are really just at the beginning of a deeper understanding of the inner workings of our planet, many of which ultimately affect our life on its surface.

This article was originally published on The Conversation. Read the original article.

Voici une “étude” des différentes croûtes terrestres de Naraïs, je vous présente leurs description :

Niveau 1 : C’est la première couche de la planète Naraïs, sa surface. C’est ici que poussent les plantes et là ou se vivent beaucoup de peuples et de mamifères.
Niveau 2 : Cette couche est constituée de terre souple et fertile, c’est là que se trouvent les racines des petites plantes et les petits animaux comme les insectes ou les vers.
Niveau 3 : Le niveau trois est la deuxième couche de terre, elle est constituée de beaucoup de restes d'animaux et de plantes mortes. Elle est très humide grâce à l’eau très proche de ce niveau. Elle fournie ainsi à la deuxième couche les nutriments et l’eau nécessaire à son bon fonctionnement. C'est aussi la que vivent des animaux plus dangereux, comme certains serpents dragon ou araignées venimeuses.
Niveau 4 : Vraisemblablement le niveau le plus important de la planète Naraïs car cette couche « éponge » transmet l’eau des sources du niveau 5 à la terre des niveaux 2 et 3 et permet une bonne irrigation de celle-ci. Sans elle les immenses territoires comme Les Grandes Plaines serait des endroits désert et sans vie. Cette couche bien qu’étant fragile, se reconstitue très rapidement.
Niveau 5 : L’énorme rivière souterraine de Naraïs, elle abrite des montres très fort et est dangereuse, seul les plus fort et courageux des tritons (comme #Mickaïl) l’utilisent pour se déplacer rapidement entre les continents. Cependant, certains chemins ont été « aménagés » par eux pour que les plus faibles puissent circuler rapidement d’un pays à l’autre dans les couloirs de l’eau (rester trop longtemps sur terre est mauvais pour eux).

Niveau 6 : Couche de rochers très solides, qui protègent le noyau et rendent la planète solide. Une légende raconte que le minerai qui a forgé l’épée légendaire la plus indestructible et la plus puissante en magie de Naraïs se trouverait cacher en dessous de ses pierres.