在特别大的地球上挖呀挖呀挖，挖到最后发现……

[1]http://www.bbc.com/future/story/20190503-the-deepest-hole-we-have-ever-dug

[2] https://en.wikipedia.org/wiki/Kola_Superdeep_Borehole

[3] http://superdeep.pechenga.ru/

[4] https://en.wikipedia.org/wiki/Structure_of_the_Earth 

[5] Andrei, Mihai (21 August 2018). "What are the layers of the Earth?". ZME Science. Retrieved 28 June 2019.[6]http://www.021diao.com/article/4939.html

[7] https://en.wikipedia.org/wiki/Project_Mohole

[8] Alan Bellows (5 March 2007). "The Deepest Hole". Damn Interesting. Retrieved 27 December 2014.

[9] G. J. MacDonald (1988). "Major Questions About Deep Continental Structures". In A. Bodén and K. G. Eriksson (ed.). Deep drilling in crystalline bedrock, v. 1. Berlin: Springer-Verlag. pp. 28–48. ISBN 978-3-540-18995-4.

[10]https://www.atlasobscura.com/places/kola-superdeep-borehole