Question 1

Rock inconstancy

Accepted Answer

Rocks look hard, rigid and immutable. But it is a matter of time perspective : in terms of geological timescales, they move, fold and go through transformations.A spectacular example : 50 million years ago, the collision of the indian and eurasian plates resulted  in the formation of the Himalayan range, a titanic clash in slow motion still ongoing to this day as the Himalayas  continue to rise by a few millimeters every year.Another surprising example : ice sheets, heavy as they are, push into the Earth's crust. As ice is melting away , the weight  decreases. Consequence? The land surface is rising slowly  : this is the post-glacial rebound  (or isostatic rebound). In Scandinavia or in Canada, the ground  can rise by several centimeters per decade.

Question 2

Funfact | The rock cycle

Accepted Answer

Rocks  form, erode,  compact and transform over millions of years… then, they do it all over and over again.

Question 3

Funfact | SG-3

Accepted Answer

The deepest drilling in the world goes as deep as 12,262 meters in the ground and  is located on the Kola peninsula (former Soviet Union).

Question 4

Funfact | Hot spot

Accepted Answer

A hot spot is where  magma rises from the depths of the Earth's mantle , which may cause volcanic eruptions. Hawaii, la Réunion, Yellowstone, the Galápagos Islands or St Helena are all hot spots.

Question 5

Ancient crusts go deep down

Accepted Answer

Oceanic trenches are created by subduction, such as the Japan Trench (9 km in depth), the Tonga Trench (10 km) and last but not least  the Mariana Trench (11 km). In this case, the Pacific's ancient oceanic crust  sinks - or subducts -   under the Philippines' younger oceanic crust and forms a subduction zone  that is so deep that the whole Himalayan range could theoritically fit in it.

Question 6

Funfact | The pumice stone

Accepted Answer

Is an ultra light volcanic rock that is formed when gas-rich lava cools so quickly that bubbles remain trapped inside and compose a porous structure.

Question 7

Funfact | The human face

Accepted Answer

A human face tends  to get wrinkled  over time, whereas that of the Earth softens : its geological folds disappear gradually  under the effect of erosion by water, frost and wind.

Question 8

Funfact | Taking root

Accepted Answer

When continental plates collide, the crust does not only thicken on the surface (mountains), but also in depth. This is referred to as a crustal root and  the  Alps' one is 55 km in depth.

Question 9

Focus on plate tectonic plates

Accepted Answer

It was not until the 1960s that scientists started to have a better understanding of the dynamics governing plate tectonics and could come up with improved models. The assemblage of plates making up the Earth's lithosphere have been described as follows :8 major plates, (very large-sized) :Africa North AmericaSouth AmericaAntarcticaAustraliaEurasiaIndiaPacific12 minor plates, (smaller sized)  :AmurArabianCarribeanCarolineCocosJuan de FucaNazcaOkhotsk Philippine SeaScotiaSomaliYangtzeAnd about 40 microplates.Most of these plates consist of  both continental and oceanic crusts  –  such as the African plate, which includes a large swathe of the Atlantic.Some plates, such as the Pacific plate, are almost entirely oceanic. Others,such as the  Amur plate, are essentially continental.

Turning plate tectonics

The Earth is a gigantic puzzle whose pieces are in perpetual motion. This waltz has been going on for at least 3.3 billion years: it has shaped the planet, with the formation of continents and mountains. It is also this waltz that causes volcanic eruptions and earthquakes.

The continental crust today has an average thickness of 35 km while the oceanic crust is much thinner, with a thickness ranging from 5 to 10 km.

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