The idea that Earth is hollow, suggesting a world of hidden spaces beneath our feet, has persisted in the public imagination for centuries. This concept proposes a vast, empty interior, perhaps housing its own sun, atmosphere, and hidden civilizations. While captivating, this notion is rooted in speculation and has been conclusively disproven by modern geophysical science. The structure beneath the surface is characterized by incredible density, heat, and pressure, not empty space.
The History and Claims of the Hollow Earth Myth
The idea of a subterranean world has ancient roots, appearing in folklore, mythology, and religious concepts of the afterlife. The modern hypothesis began in the late 17th century with astronomer Edmond Halley. He proposed that Earth consisted of multiple concentric shells separated by atmospheres to explain anomalous readings in the planet’s magnetic field. Halley suggested these shells rotated at varying speeds and were possibly inhabited.
In the 19th century, John Cleves Symmes Jr., an American army officer, popularized the concept. Symmes claimed the Earth was a shell about 800 miles thick with large, curving openings at the North and South Poles, known as “Symmes’ Holes.” Proponents often claimed the interior contained an inner sun, lush vegetation, and advanced civilizations, like the mythical Agartha. These imaginative concepts have kept the hollow Earth idea alive as a persistent piece of pseudoscience.
How Scientists Know the Earth is Not Hollow
The most compelling evidence against a hollow Earth comes from seismology, the study of seismic waves generated by earthquakes. Scientists track how these waves travel through the planet’s interior, and the observed patterns are incompatible with a hollow structure.
There are two main types of body waves: P-waves (primary) and S-waves (secondary). P-waves travel through both solids and liquids, but their speed changes when moving between materials of different density. S-waves, however, cannot travel through liquid and are blocked by molten material. The recorded travel times and pathways show that the interior is filled with material of increasing density, including a liquid layer that blocks S-waves entirely.
Further proof comes from gravitational measurements and the Earth’s total mass. If the planet were a hollow shell, its average density would be far too low to account for the gravitational pull experienced on the surface. Earth’s measured average density is approximately 5.51 grams per cubic centimeter, which requires an interior composed of extremely dense, compressed material. Furthermore, a hollow shell would collapse under its own gravity, as ordinary matter cannot support a planetary-sized empty structure against immense forces.
The True Layers Beneath Our Feet
The interior of the Earth is structured into distinct, high-density layers that transition from the rocky surface to a metallic, superheated center. This structure is typically divided into three main chemical layers: the crust, the mantle, and the core. The outermost layer is the crust, which is relatively thin, ranging from about 5 kilometers under the oceans to about 40 kilometers under the continents. Continental crust is primarily composed of granite, while the oceanic crust is made of denser basalt.
Beneath the crust lies the mantle, which extends to a depth of about 2,900 kilometers and makes up approximately 80% of the Earth’s volume. This layer consists of very hot, dense rock rich in iron and magnesium silicates, yet it remains mostly solid. The extreme heat, which can range from 1,000°C to over 4,000°C, allows the material in the upper mantle to behave plastically, flowing very slowly over geologic timescales.
The core begins at the base of the mantle and is divided into two parts: the outer core and the inner core. The outer core is approximately 2,300 kilometers thick and is composed of liquid iron and nickel. Temperatures here are incredibly high, ranging between 4,000°C and 6,000°C, and the convection currents within this liquid metal generate the Earth’s magnetic field.
Finally, the innermost layer is the inner core, a solid sphere of iron and nickel with a radius of about 1,220 kilometers. Despite being the hottest part of the planet, with temperatures reaching up to 6,000°C, the inner core remains solid. This is because the immense pressure from all the overlying layers compresses the metal atoms so tightly that they cannot melt, keeping the center of our planet a dense, solid ball.