Much like the surface of the Moon and Mars, the depths of the ocean, and the uncharted expanse of the Milky Way, the interior of our planet was at the mercy of imagination in the formative years of modern civilisation. Was the Earth solid or hollow within?
The possibility of an alternate Earth beneath our collective feet was a fascinating prospect for people without the technology to peer beneath the planet’s crust; a land similar to our own, yet as unknown as the distant planets, a potential Garden of Eden sequestered beneath the soil.
The French author, Jules Verne, brought the ‘hollow globe theory’ to the public consciousness with his 1864 novel, Journey to the Centre of the Earth. Edgar Rice Burroughs added his own take in 1914 with At the Earth’s Core. The Nazi Party then claimed the idea for their own nefarious ends in the 1940s.
However, Verne, Rice Burroughs, and the Third Reich were merely torch-bearers for their luminaries.
- Russian Dolls
The belief in the Earth as an empty shell was old news even in the seventeenth century, some two hundred years before Verne charted Axel and the Professor’s descent into the Icelandic volcano, and three centuries before Adolf Hitler (allegedly) absconded into the depths of our planet.
Edmond Halley, an English scientist best known for the eponymous comet, 1P/Halley, was poking holes in the Earth in 1692. Halley envisioned a world not unlike a Matryoshka doll, in which different planes of the Earth lived within one another, each separated by an atmosphere.
As demonstrated by the man himself (right), the smallest sphere was, in fact, a solid ball – the Earth’s core; around it were shells that corresponded in size to our celestial neighbours, Mercury, Venus, and Mars. The plane with which we are most familiar, the world of mammals and birds, enclosed the nest of spheres.
The Aurora Borealis and Aurora Australis, Halley claimed, were formed when gas escaped through the holes at the two poles, the most northern of which is commonly cited as being in the region of the 62nd parallel.
While Halley was ostensibly uninterested in testing his hypotheses, choosing instead to venture into finance and life annuities, the 19th century brought about men who were willing to stake their reputation on finding an entrance into the Earth’s vacant interior.
- Thrifty Vegetables
John Cleves Symmes, Jr. was a former captain of infantry, and a man who believed that the interior of our planet was “hollow and habitable within.
“…containing a number of solid concentrick [sic] spheres, one within the other, and that it is open at the poles twelve or sixteen degrees.
“I pledge my life in support of this truth, and am ready to explore the hollow, if the world will support and aid me in this undertaking.”
In 1818, Symmes sought explorers to accompany him on an expedition to Siberia, Russia, in the autumn, “with reindeer and sleighs, on the ice of the frozen sea.” He hypothesised a world of plenty beneath the iron-hard ground, complete with “thrifty vegetables and animals, if not men.”
Surprisingly, Symmes found some support for his theory from the then-President of the United States, John Quincy Adams. However, any hope of an expedition was lost when Adams left office; his replacement, Andrew Jackson, was apparently none too fond of Symmes ideas.
- Seismic Waves
Like many fantastic theories from the eighteenth and nineteenth centuries, the ideas of Symmes and Halley quickly became a casualty of scientific observation, now lumped in with astrology, phrenology, electronic voice phenomenon, and other pseudo-scientific mumbo-jumbo.
There are many arguments against the possibility of a hollow planet – that gravity would cause the body to collapse; the fact that planetary accretion does not create empty shells, and the Earth would have to be ‘hollowed out’ from the inside – and very few in favour.
Accepting, for a moment, the possibility of a hollow planet and life within, humanoid denizens would struggle to survive in the earth’s interior. Gravity may be just 1/300th of that on the outer surface, meaning that our subterranean dwellers would be nearly weightless.
Of course, as the human species has delved no deeper than 12.3km (or 0.1875%) into our planet’s bulk, elements of our planet’s interior may yet prove surprising. The texture and consistency of the Earth’s viscera is inferred through the use of seismic waves.
That is not to say that Symmes and Halley’s observations will one day be proven true but the mantle and core of our planet remain fertile ground for science-fiction writers nevertheless, just as Mars, the Moon, and the abyssal wastes of the Pacific Ocean continue to stir our imagination to this day.