Researchers unlock secrets of Earth’s wickedly hot innermost realm
SMA NEWS – WASHINGTON
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.
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.
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.
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.
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.