Let's continue our overview of our planet's inside.
In Jojo vs Earthquake (Part 3) I listed the four big layers composing Earth. In that part I also covered the Crust Layer. Today, going deeper and below the Crust, we meet the Mantle.
THE MANTLE LAYER
The Mantle is the biggest part of our planet with its 2,900 Km (1,802 Miles) thickness, it represent 84% of the whole volume of the planet, and 64% of its entire mass. It is there that usually the big activity is going on : Convection current and Magma formation, as well as contribution to mountain formation (orogeny).
The Crust itself, the part on which we live, is at the receiving end of that action resulting in earthquakes, volcanic activity, seafloor spreading, continental drift, and Plate Tectonic.
The Mantle is also particularly hot, and the deeper you go, the hotter it gets. For instance, near the boundary between the Crust and the Mantle it is 1000°C (1832°F), on the other end, near the Mantle and Upper Core boundary, the temperature reaches 3700°C (6692°F).
Although it is considered, in simple general term, as one big solid layer, it is a misconception. Scientist have divided it in four different zones, each with really different qualities - Upper Mantle, Transition Zone, Lower Mantle, D''
Upper Mantle
That first zone, around 410 Km (255 Miles) thick, extend from the Crust to the Transition Zone. Mainly solid, it contains more fluid part (for instance, rock in thick liquid form like Lava) at the level of the asthenosphere (the part of the Mantle which is between the Crust and the Mantle).
Transition Zone
The second zone of the Mantle is around 250 kilometers thick (between 410Km and 660Km beneath Earth's Surface). In that zone, the rocks transforms and their crystalline structure changes radically. The rocks, although submitted to high pressure and heat, does not melt or disintegrate but they get way more dense.
Lower Mantle
The third zone is called, simply enough, the Lower Mantle. Around 2,050 Km thick, it extend from 660km to around 2,700Km beneath Earth's Surface. That zone is hotter and denser than the two preceding zones. The Lower Mantle zone is still subject to a lot of debate and research.
D'' (D prime prime)
Finally, we arrive at the last and fourth zone of the Mantle called D'' (D double prime), a fancy name for another Transition Zone. I know it's a strange name, but they like it like that. That zone extend from 2,700Km to 2,900Km beneath the Earth's Surface (around 200Km thick).
Because of its complexity D'', like the Lower Mantle zone, is still subject to debate and research.
Here we are, deep in the Earth, just at the boundary with the super hot Upper Core (they even gave a name to that boundary - the Gutenberg Discontinuity). So, next time we will jump into hot liquid nickel-iron toward the last layer of our dear planet.
Mabuhay!
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