Scientists unlock secrets in Earth’s wickedly hot, innermost realm

WASHINGTON, Feb 21 (Reuters) – In Jules Verne’s classic 1864 novel “Journey to the Center of the Earth,” adventurers descend through an Icelandic volcano into a vast underground world populated by prehistoric creatures as they explore the planet’s interior. The actual center of the Earth is nothing like this fanciful depiction – and in some ways is even more dramatic.

Scientists said Tuesday 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 inside the planet’s inner core — a vicious, innermost solid ball of iron and nickel about 800 miles (800 miles ) 1350 km) wide.

Earth’s diameter is about 7,900 miles (12,750 km). The planet’s internal structure consists of four layers: a rocky outer crust, then a rocky mantle, an outer core made of magma, and a solid inner core. This metallic inner core, about 1,500 miles (2,440) wide, was discovered in the 1930s, also based on seismic waves traveling through the Earth.

Researchers in 2002 suggested that lurking in this inner core was an innermost part separate from the rest, akin to a Russian Matryoshka nesting doll. The increasing sophistication of seismic monitoring made it possible to confirm this.

Earthquakes unleash seismic waves that travel through the planet and can reveal the contours of its internal structure based on the waves’ changing shape. Until now, scientists have been able to detect these waves bouncing up to twice, from one side of the Earth to the other and then back. The new research studied waves from 200 magnitude-6.0 earthquakes that ricocheted like ping-pong balls up to five times on the planet.

“We may know more about the surface of other distant celestial bodies than the deep interior of our planet,” said observational seismologist Thanh-Son Pham of the Australian National University in Canberra, lead author of the study published in the journal Nature Communications.

“We analyzed digital records of ground motion, known as seismograms, from large earthquakes over the past decade. Our study is made possible by the unprecedented expansion of the global seismic networks, particularly the dense networks in the contiguous United States, the Alaska Peninsula, and across the European the Alps,” Pham added.

The inner core’s outer shell and its newly confirmed innermost sphere are both hot enough to melt, but are a solid iron-nickel alloy because the incredible pressure at the center of the Earth turns it into a solid state.

“I like to think of the inner core as a planet within the planet. It’s actually a solid ball, about the size of Pluto and slightly smaller than the Moon,” said Hrvoje Tkalčić, a geophysicist and study co-author at the Australian National University. .

“If we were somehow able to dismantle the Earth by removing its mantle and the liquid outer core, the inner core would appear shining like a star. The temperature is calculated to be about 5500-6000 degrees (Celsius/ 9,930-10,830 Fahrenheit), similar to the Sun’s surface temperature,” Tkalčić said.

The transition from the outer part of the inner core to the innermost sphere appears to be gradual rather than a sharp boundary, Pham said. The researchers were able to separate the two regions because the seismic waves acted differently between them.

“It could be caused by different arrangements of iron atoms at high temperatures and pressures or the preferred alignment of growing crystals,” Pham said.

The inner core slowly grows in size at the expense of the outer core by solidifying molten materials as Earth gradually cools – as it has done since its birth some 4.5 billion years ago.

“The latent heat released from solidifying the Earth’s inner core drives the convection in the liquid outer core, generating the Earth’s geomagnetic field,” Pham said. “Life on Earth is protected from harmful cosmic rays and would not be possible without such a magnetic field.”

Reporting by Will Dunham, editing by Rosalba O’Brien

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