Scientists find out what’s inside the hottest part of the Earth

In the famous 1864 novel Journey to the Center of the Earth by Jules Verne, intrepid explorers descend through an Icelandic volcano onto a vast underground world inhabited by prehistoric species. In some ways, the actual heart of the planet is even more striking than this fantastical image.

Tuesday, February 21, researchers announced that an intensive study of Earth’s deep interior, based on the behavior of seismic waves from large earthquakes, confirmed the existence of a distinct structure within our planet’s inner core – a wickedly hot innermost solid ball of iron and nickel approximately 800 miles (1,300 km) in diameter.

The diameter of the Earth is around 7,900 kilometers (12,750 km). The underlying structure of the planet consists of four layers: an exterior rocky crust, a rocky mantle, a magma-filled outer core, and a solid inner core. This roughly 1,500-mile-wide (2,440-kilometer-wide) metallic inner core was identified in the 1930s, also based on seismic vibrations passing through Earth.

In 2002, scientists hypothesized that this inner core contained a distinct deepest part, similar to a Russian Matryoshka nesting doll. This was verified by the increased sophistication of seismic monitoring.

Earthquakes release seismic waves that travel through the planet and, based on the changing shape of the waves, can reveal the interior structure of the planet. Until now, scientists have been able to detect these waves bouncing from one side of the Planet to the other and back again. The latest research examined waves from 200 earthquakes with magnitudes greater than 6.0 ricocheting within the planet up to five times like ping-pong balls.

Thanh-Son Pham, an observational seismologist at the Australian National University in Canberra and main author of the study published in the journal Nature Communications, stated, “We may know more about the surface of distant celestial bodies than the inside of our planet.”

“We evaluated seismograms, which are computerized records of ground motion from big earthquakes over the past decade. Our analysis is made possible by the exceptional expansion of worldwide seismic networks, especially the dense networks in the contiguous United States, the Alaskan peninsula, and the European Alps,” Pham explained.

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The outer shell of the inner core and its newly verified innermost sphere are both hot enough to be molten, but are a solid iron-nickel alloy due to the immense pressure at the heart of the Earth.

“I like to consider the inner core as a separate planet within the globe. Actually, it is a solid ball, roughly the size of Pluto and slightly smaller than the moon,” according to Hrvoje Tkali, a geophysicist and co-author of the study from the Australian National University.

“If we were able to disassemble the Earth by removing its mantle and liquid outer core, the inner core would resemble a brilliant star. Its temperature is believed to be between 5,500 and 6,000 degrees Celsius, which is comparable to the surface temperature of the sun,” Tkali stated.

Pham stated that the transition from the outermost portion of the inner core to the innermost sphere appears gradual rather than sharp. The researchers were able to distinguish between the two regions because their seismic waves behaved differently.

“Different configurations of iron atoms at high temperatures and pressures or the preferred orientation of developing crystals may be responsible,” Pham explained.

The inner core is expanding at the expense of the outer core due to the solidification of molten minerals as the Earth cools, as it has done since the planet’s formation some 4.5 billion years ago.

“The latent heat generated by the solidification of the inner core of the Earth causes the convection in the liquid outer core, so generating the geomagnetic field of the Earth,” explained Pham. Without such a magnetic field, it would be impossible for life to exist on Earth, as it is protected from deadly cosmic rays.

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