The structure of the geosphere

Explain what the geosphere is and name which other parts of the Earth it is in contact with at the surface (air, water, and living things), writing the technical name for each one.

The cross-section in the figure shows the concentric layers of the geosphere, but one of them is marked with "?". State the name of that layer and list all the layers in order from the shallowest to the deepest.

Name the three layers of the geosphere and state which is the outermost and which is the deepest. Which layer do we live on?

Which is the thinnest layer of the geosphere? Compare its maximum thickness ($70\ \text{km}$) with that of the mantle (about $2\,900\ \text{km}$) and explain what that difference means.

Distinguish between continental crust and oceanic crust: which of the two is thicker, where each one is located, and what types of materials predominate in them.

Continental crust is thicker and less dense than oceanic crust. Using the analogy of two icebergs of different thickness, explain why continents rise above sea level while oceanic crust remains submerged.

Where do you think the crust is thicker: under the Himalaya mountain range or under the Pacific Ocean? Justify your answer and explain the relationship between high mountains and the deep "roots" of the crust.

State the physical state of the materials of the outer core and the inner core, and explain which two metals they are mainly made of.

The iron in the core causes the Earth to behave like a giant magnet.

1. a) Explain which everyday device makes use of this magnetism to navigate.
2. b) Reason out what would happen to that device if the core were not magnetic.

The core has a liquid outer part and a solid inner part, even though both are made of iron and nickel. Explain how it is possible for the inner core, being the hottest region of the planet, to remain solid.

Where does the heat inside the Earth come from? Explain two sources of this heat (the heat left over from the formation of the planet and the heat generated by certain materials inside it) and name two pieces of evidence of this heat that we can observe at the surface, such as volcanoes or hot springs.

The Mponeng gold mine (South Africa) is the deepest human excavation on Earth: it reaches nearly $4\ \text{km}$ beneath the surface. In that area, the surface temperature is $20\ ^\circ\text{C}$ and the average geothermal gradient is $2{,}5\ ^\circ\text{C}$ for every $100\ \text{m}$ of depth.

1. a) Calculate what temperature the rock at the bottom of the mine would reach if no artificial air conditioning system were operating.
2. b) A miner can only work safely if the ambient temperature does not exceed $32\ ^\circ\text{C}$. Calculate the maximum depth at which this safety limit would be reached without cooling.
3. c) If we applied that same gradient continuously to the center of the Earth ($6\,371\ \text{km}$), what absurd theoretical temperature would be obtained in the core? Deduce what this calculation teaches us about how the geothermal gradient varies in the deepest layers.