I was just reading this:

https://futurism.com/2018-looking-back-century

The perhaps vulgar term “futurology” is better than the publication’s chosen one (“futurism”, which is easily confused with, well, “Futurism”…  https://en.wikipedia.org/wiki/Futurism)

“We can take coal out of a mine, but we can never put it back. We can draw oil from subterranean reservoirs, but we can never refill them again. We are spendthrifts in the matter of fuel and are using our capital for our running expenses. In relation to coal and oil, the world’s annual consumption has become so enormous that we are now actually within measurable distance of the end of the supply. What shall we do when we have no more coal or oil!” [Alexander Graham Bell, speaking in 1917].

We see from the above that even the greatest inventive minds often predict incorrectly. “Peak oil” has been predicted for over a century. The only certainty is that any specified commodity is limited in quantity, at least on this planet.

There again, the reality is that, for all human exploration and scientific discovery, we do not know a great deal for sure about what lies under our feet. The deepest mines in the world go only about 2.5 miles from the surface of the Earth, while the deepest natural caves go not even as deep as that.

https://en.wikipedia.org/wiki/List_of_deepest_mines

https://en.wikipedia.org/wiki/List_of_deepest_caves

Of course, most of us “know”, having read it, or been told it at school, that the Earth is composed, at most basic, of Crust, Mantle, and Core. The Crust is supposed to be between 20-30 miles thick (Continental; Oceanic 3-6 miles). Some estimates say 43.5 miles at thickest.

https://en.wikipedia.org/wiki/Earth%27s_crust

https://en.wikipedia.org/wiki/Structure_of_the_Earth

The deepest mine is 2.5 miles deep (it is planned to go 1-2 miles deeper). So the deepest below the surface any human being has actually been is maybe 3 miles, whereas the Continental crust is as much as 43.5 miles. So human beings have only been one-seventeenth (or one-fifteenth) as deep as the extent of even the crustal zone of the Earth.

The deepest boreholes on Earth still go only about 8 miles deep:

https://en.wikipedia.org/wiki/Travel_to_the_Earth%27s_center

Human ideas of what lies below the Crust rely on a mixture of observation, analogy, mathematical, physical and chemical experimentation, surmise, and simple speculation. The deeper the layer, the less is actually known.

“The inner core was discovered in 1936 by Inge Lehmann and is generally believed to be composed primarily of iron and some nickel.

The liquid outer core surrounds the inner core and is believed to be composed of iron mixed with nickel and trace amounts of lighter elements.

Recent speculation suggests that the innermost part of the core is enriched in gold, platinum and other siderophile elements.^[29]” [Wikipedia]

Note the language: “is generally believed to be“, “is believed to be“, “recent speculation suggests that…” and so on. That is not to disparage the immense amount of work done by highly intelligent and qualified persons, but the bottom line is that they do not know.

We have seen that human intrusion into the Earth, even remotely (via drill) goes only 8 miles deep. The radius of the Earth is taken to be 3,963 miles. So humans have only penetrated 1/495th into the Earth (and by actual human visitation, 1/1321). We do not really know what is there.

There have been alternative views of what lies deep in the Earth. Rudolf Steiner postulated a number of layers (I think nine) under the surface:

https://www.bookdepository.com/Interior-Earth-Rudolf-Steiner/9781855841192

He claimed to be aware of these layers via his clairvoyant gifts.

There is no conclusion to this brief article. I just wanted to remind myself and others that there is a huge amount that we do not yet know about the way our world is.

Notes

https://steiner.presswarehouse.com/books/BookDetail.aspx?productID=151235

https://steiner.presswarehouse.com/Books/BookDetail.aspx?productID=565635

https://wn.rsarchive.org/GA/GA0335/19200310p01.html

https://www.rsarchive.org/RelAuthors/ArensonA/InterioroftheEarth.php

https://www.anthroposophy.ca/wp-content/uploads/2018/04/Keppie-Body-Soul-Spirit-Earth.pdf

http://888spiritualscience.blogspot.com/2012/02/upon-subject-of-saturation-of-earth.html

https://en.wikipedia.org/wiki/Rudolf_Steiner