This is a discussion about what is underground, according to the Flat Earth Theory.
Here are some references I found on the FAQ to things under the ground:
"Q: 'What is underneath the Earth?'
A: This is unknown. Most FE proponents believe that it is generally composed of rocks. Please note that in Hinduism, the Earth rests on the back of four elephants and a turtle."
So, we're noting this, but not accepting it, apparently.
"Rocks" could mean molten rock, and there certainly are volcanoes on Earth, but the plural form of this seems to suggest multiple rocks, which is meaningless in the concept of magma. There is no experimental proof or even a reason for making such a claim.
"Q: 'Exactly what shape is the Earth if it is flat? Square or circle?'
A: Circle, like in the UN logo. However, the earth is NOT 2D; it is in the shape of a cylinder."
This is the only mention of this. No experimental proof is given.
"Q: 'How do volcanic eruptions happen?'
A: The Earth is thick enough to have a core of molten lava. Once there is too much of it in too confined a space, it finds its way out, just like the water will come out of a full bottle if you squeeze it too hard."
This implies that there
is a core. Core is generally meant to mean "center," (the core of an apple, the core of one's body) which implies that perhaps there is another side to the Earth? It also implies that somehow, lava is either added, into a finite space, so that it can be squeezed out, or that this space is compressed. It also implies that there is no solid core, like in the Round Earth Theory, but simply lava all the way through to an alleged other side.
I also searched "under the earth" in quotes across the whole forum. I found things such as "We don't know. Neither does RET," "There are four elephants and a turtle," "Dark energy," "The sun moves under the Earth," and (mostly) there seems to be a general consensus that there is another side.
What does experimental science tell us? Well, we can only deduce things based on properties of seismic waves and such.
The following passage is from this URL:
http://www.sciencedaily.com/releases/1998/12/981211083655.htmConfirming a long-held scientific notion, a Northwestern University seismologist and a colleague at the French Atomic Energy Commission have provided the first direct evidence that -- inside a liquid core -- the very center of the Earth is solid.
The long sought finding, which had been hinted at but never proven, came from analysis of seismic waves generated by the June 1996 earthquake in Indonesia and recorded at a large-array seismic network spread across France. The finding will be presented Thursday at the American Geophysical Union meeting in San Francisco and will appear in the Dec. 15 issue of Earth and Planetary Science Letters.
For decades, seismologists have used seismic waves as a sort of probe of the Earth's insides. They look at how the waves created by an earthquake at the surface of the Earth reverberate through the interior before being detected on the other side.
"The general picture of the Earth at the turn of the last century was that it had a rocky mantle floating on a liquid core of molten iron," says Emile A. Okal, professor of geological sciences at Northwestern and an author of the new study. The fluidity of the iron explained the existence of the Earth's magnetic field, he said.
But geophysicists also assumed that at some great depth, the pressure would be so high that even at temperatures of thousands of degrees the iron would freeze solid. In the 1930s, seismologists did find a "discontinuity" in the velocity of waves propagated through the center of the Earth, suggesting some sort of stratification of the core.
The problem, for 60 years now, is that those waves never carried the signature of a solid.
"A solid has a very distinctive mechanical property, which is that it can sustain two different kinds of waves," Okal said. "It can transmit a wave that oscillates in the direction of travel, sort of a pulsing compression-and-relaxation, and it can transmit a wave that vibrates perpendicular to the direction of travel, like a guitar string."
A liquid can propagate only the first type of wave, which corresponds to a change of volume and pressure, as it propagates, he said. "The second type requires memory of a shape for its restoring force, and a liquid has no shape."
Only the first type of wave, characteristic of liquids, had ever been observed coming from the Earth's core.
Okal and his colleague in France, Yves Cansi, used an eight-station French seismic network to study the Indonesian earthquake, and for the first time detected the telltale second vibration.
"The 1996 Flores Sea earthquake, which was a big earthquake at about 600 kilometers depth, was perfect in geometry for recording in France," Okal said. "If you want to sample the deepest part of the Earth, you need a big, deep earthquake," he said. "And they are rare." A deep earthquake gives rise to cleaner signals, he said.
Improvements in instrumentation over the last 15 years were crucial to the new finding, Okal said, as were computer capabilities, developed in France, to extract signals from noise.
Okal's expectations for the significance of the finding are, well, down to earth.
"We look at the interior of the Earth because we would like to know what is below us," Okal said. "But this may turn out to be interesting to the field of materials science because it indicates that under tremendous pressures, iron is behaving in a different way," he said. "Understanding how the qualities of materials are affected under extremely high pressures -- millions of times the atmospheric pressure -- might be applicable for different materials at not-so-heavy pressures."
The research was supported by the National Science Foundation.
The data is, of course, based on the assumption of a round Earth, and therefore, measurements are accounted for in this manner. Therefore, if the Earth were flat, we would have to justify this, which is impossible. According to RET, the Earth is round and the core is round; to convert this, with the correct distances from points on the surface to points on the edge of the core, we would need a flat Earth and a flat core. This will, unfortunately, affect the seismic waves, because it is now at a different angle. You cannot have a flat core and an angled core that will reflect seismic waves in exactly the same way it does in a RET. Therefore, it is completely impossible to explain this using FET.