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[[Category:Done 2015-08-21]]
[[category: Lecture 1A_a_changing_planet]]
[[File:Earth-crust-cutaway-english.png|framed| Figure 1: The Earth and its interior layers.<ref>Wikimedia Commons [Public Domain], Available: http://commons.wikimedia.org/wiki/File:Earth-crust-cutaway.png</ref>]]
<onlyinclude>The '''Cross section of the Earth''' is a visualization of the composition of the Earth in geological terms. The planet Earth is an immensely complicated and dynamic system, with many different physical and chemical properties.</onlyinclude> Most human experience of the Earth is limited to the surface however, with the deepest human endeavor made in 2012 to depths of 11 km in the Mariana's Trench.<ref>National Geographic (2012) ''James Cameron Completes Record-Breaking Mariana Trench Dive'' [Online] Available: http://news.nationalgeographic.com/news/2012/03/120325-james-cameron-mariana-trench-challenger-deepest-returns-science-sub/</ref> In fact, the deepest humans have ever managed to drill into the Earth at 12.3 km isn't much deeper, at a drilling site known as the Kora Superdeep Borehole.<ref>Atlas Obscura (n d) ''KOLA SUPERDEEP BOREHOLE'' [Online] Available: http://www.atlasobscura.com/places/kola-superdeep-borehole</ref> These are impressive distances and require incredible technology, but in the context of the whole Earth, these distances are extremely small. For a feel of how small these depths are, the radius of the Earth is about 6371 km, making the deepest hole humans have ever drilled a mere 0.2% of the way to the centre of the Earth. This distance is about a quarter way through the Earth's '''crust''', which is the top layer in the cross section of the Earth. The crust is made up of igneous, metamorphic and sedimentary rocks, and the entirety of the crust only makes up around 1% of the Earth's volume.<ref>Universe Today. (2009). ''Earth's Crust'' [Online] Available: http://www.universetoday.com/26750/earths-crust/</ref>

Deep into the centre of the Earth lies the Earth's '''core''', consisting of a solid iron-nickel alloy at extremely high [[temperature]]s, about the same temperature as the surface of the [[Sun]].<ref>D. Alfè; M. Gillan & G. D. Price (January 30, 2002). "Composition and temperature of the Earth's core constrained by combining ab initio calculations and seismic data" (PDF). Earth and Planetary Science Letters (Elsevier) 195 (1–2): 91–98. Bibcode:2002E&PSL.195...91A. doi:10.1016/S0012-821X(01)00568-4.</ref> The Earth's inner core is solid due to the fact that the immense [[pressure]] at that depth increases iron and nickel's [[melting point]] to above these temperatures, resulting in solidified core. The temperatures of the core are very high due a number of factors. One reason is that the Earth, when formed, was incredibly hot and it takes a very long time for this [[heat]] to be lost by [[convection]] currents. In the 19th century it was predicted that the Earth should cool off in millions of years,<ref>J.D. Burchfield, ''Lord Kelvin and the Age of the
Earth'', University of Chicago Press, 1990.</ref> but the Earth's timescale is much longer than that.

Rutherford proposed the reason for the continual heat of the Earth's core, which is due to [[radioactive]] heating caused by the [[radioactive decay|decay]] of [[element]]s such as [[Uranium]] and [[Thorium]]. These elements aren't found in the core however, with the most popular model suggesting that they are found in the '''lithosphere''' and '''mantle'''. This form of heating is said to account for 50% of the Earth's heat, with the other heat coming from the primordial heat of the Earth.<ref>Physics World. (2011). ''Radioactive decay accounts for half of Earth's heat'' [Online] Available: http://physicsworld.com/cws/article/news/2011/jul/19/radioactive-decay-accounts-for-half-of-earths-heat</ref>

The video below is a lecture from Prof. David Shultz, University of Manchester,<ref name = Shultz>Prof. David Shultz has graciously allowed the use of this and other videos in a private communication with Jason Donev.</ref> talking about what the cross section of the Earth looks like:
<HTML5video width="800" height="450" autoplay="false" loop="true">Inside_the_Earth</HTML5video>

Here's another video with Prof. Shultz<ref name = Shultz /> talking about how scientists have figured out what's inside the Earth using seismic (earthquake) data:
<HTML5video width="800" height="450" autoplay="false" loop="true">Know_Inside_the_Earth</HTML5video>

For more information about the interior of the Earth, visit [http://pubs.usgs.gov/gip/interior/ USGS].

==References==
{{reflist}}
[[Category:Uploaded]]

Cross section of the Earth - Revision history

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J.williams at 16:49, 12 August 2015