New research – CNN.co.jp – in the deepest part of the Earth

2023.02.24 Posted Fri at 09:20 JST

（ＣＮＮ） In the inner core at the center of the Earth, there is a hidden layer that can be called the “innermost inner core”. Researchers at the Australian National University published such findings in a paper published in the scientific journal Nature Communications.

The Earth is thought to have four layers, the crust, mantle, molten outer core, and solid inner core, in order from the surface. This discovery, which indicates the existence of a fifth layer, could provide new clues to long-standing mysteries about the Earth and its composition.

For nearly two decades, scientists have suspected that there is a new, unknown layer in the Earth’s core. According to the research paper, new measurements of seismic waves passing through the center of the Earth revealed the deepest core.

Seismic waves are generated by earthquakes and volcanoes and propagate through the crust and into the Earth’s interior. The study is the first to capture seismic waves from a giant earthquake bouncing from one side of the Earth to the other, up to five times. Tansan Pham, a co-author of the paper and a seismologist at the Australian National University Institute of Geosciences, explains in an email.

The layer found is a 400-mile-diameter metal ball, Huang said, so similar in composition to the layer directly above it that it was never discovered. Both the new layer and the outer layer are alloys of iron and nickel with a few other elements.

Both the deep layer and the outer inner layer are hard. The change between the two layers is gradual rather than abrupt, so direct reflection of seismic waves did not find the innermost layer.

The analysis focused on the speed of seismic waves in different directions as they pass through the core

Using a device that detects vibration waves, the researchers discovered that the inner core in its deepest part has a unique “contrast”. Anisotropy is an inherent property of a material that exhibits different properties depending on the angle at which the material is approached. An example of anisotropy is that when splitting firewood, it is easier to split along the grain than to split against the grain.

The researchers looked at the speeds of seismic waves traveling in different directions through the core and found that the speed changes in the innermost inner core were different from those in the upper layers.

The presence of new layers can help us understand past and future changes in Earth’s magnetic field. Pham said: “On Mars, we still don’t understand why it disappeared[المجال المغناطيسي للكوكب]”.