Scientists unlock secrets of Earth's wickedly hot innermost realm
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[February 22, 2023]
By Will Dunham
WASHINGTON (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 our planet's interior. The actual center of the Earth is
nothing like this fanciful depiction - and in some ways is even more
dramatic.
Researchers on Tuesday said 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 our planet's inner core - a
wickedly hot innermost solid ball of iron and nickel about 800 miles
(1,350 km) wide.
Earth's diameter is about 7,900 miles (12,750 km). The planet's internal
structure comprises four layers: a rocky crust on the outside, 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 Earth.
Scientists in 2002 proposed that lurking within this inner core was an
innermost section separate from the rest, akin to a Russian Matryoshka
nesting doll. The increasing sophistication of seismic monitoring
enabled this to be confirmed.
![](http://archives.lincolndailynews.com/2023/Feb/22/images/ads/current/graue_lda_22COLORADOpreowned_022023.jpg)
Earthquakes unleash seismic waves that travel through the planet and can
reveal the contours of its interior structure based on the changing
shape of the waves. Until now, scientists were able to detect these
waves bouncing up to twice, from one side of Earth to the other and then
back. The new research studied waves from 200 quakes with magnitudes
above 6.0 ricocheting like ping pong balls up to five times within 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 in the last decade. Our study becomes possible
thanks to the unprecedented expansion of the global seismic networks,
particularly the dense networks in the contiguous U.S., the Alaskan
peninsula and over the European Alps," Pham added.
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![](../images/022223PIX/news_h80.jpg)
A 'Blue Marble' image of the Earth taken
from the VIIRS instrument aboard NASA's most recently launched
Earth-observing satellite - Suomi NPP, received by Reuters January
25, 2012. REUTERS/NASA/Handout
![](http://archives.lincolndailynews.com/2023/Feb/22/images/ads/current/llm_lda_ANIMAL_2023.png)
The inner core's outer shell and its newly confirmed innermost
sphere both are hot enough to be molten but are a solid iron-nickel
alloy because the incredible pressure at the center of the Earth
renders it a solid state.
"I like to think about the inner core as a planet within the planet.
Indeed, it is a solid ball, approximately the size of Pluto and a
bit smaller than the moon," said Australian National University
geophysicist and study co-author Hrvoje Tkalčić.
"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. Its temperature is estimated to be about
5,500-6,000 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 differentiate 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 is slowly growing in size at the expense of the outer
core by solidifying molten materials as Earth gradually cools - as
it has done since its birth about 4.5 billion years ago.
![](http://archives.lincolndailynews.com/2023/Feb/22/images/ads/current/charrons_bch_2022.png)
"The latent heat released from solidifying the Earth's inner core
drives the convection in the liquid outer core, generating 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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